PDF - COST FP0904

Transcrição

PDF - COST FP0904

Cost-Workshop
“Mechano-Chemical transformations of wood during Thermo-Hydro-Mechanical processing”
COST Action FP0904
Thermo-Hydro-Mechanical
Wood Behaviour and Processing
Program &
Book of Abstracts
Workshop
“Mechano-Chemical
transformations of wood
during Thermo-HydroMechanical processing”
February 16-18, 2011
Biel, Switzerland
Preface ...........................................
3
Workshop Organisation ..................
4
Tourist Information...........................
5
Scientific Program ...........................
7
Abstracts .........................................
15
Author Index ....................................
157
Cost-Action FP0904
Edited by:
Parviz Navi and Andreas Roth
Berne University of Applied Sciences
Architecture, Wood and Civil Engineering
Solothrunstrasse 102, CH - 2500 Biel
www.ahb.bfh.ch
ISBN:
978-3-9523787-0-0
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Preface
The book of abstracts includes the scientific program and the extended abstracts of papers
presented at the first COST Action FP0904 meeting on Mechano-chemical
transformations of wood during Thermo-Hydro-Mechanical processes in
Biel/Bienne on 16–18 February 2011.
The main objective of COST Action FP0904 is to achieve a better understanding of
mechanical and chemical transformations of wood during Thermo-Hydrous (TH) / ThermoHydro-Mechanical (THM) processing through collaborations between various researchers
from the wood and material sciences. This Action provides cooperation and encourages
research between research groups from academia and industry to help to overcome the
challenges being faced in scaling-up research findings, improving full industrial production,
process improvement, in understanding the relations between the processing parameters,
materials properties and the development of new products. The COST Action FP0904
consists of three Working Groups (WG):
WG1: Chemical degradation of wood under Thermo-Hydrous treatment
WG2: Modelling of Thermo-Hydro-Mechanical behaviour of wood during processing
WG3: Innovation and new products by Thermo-Hydro-Mechanical processing
The objectives of this workshop is to present and discuss the state of art in THM and TH
processing in open and closed systems, to identify the problems being faced in transferring
the laboratory research finding to industrial production, to get a better understanding of the
processing needs, the process improvement, the development of new ideas and new
products. The workshop will bring together experts and young scientists from European
academia as well as from other countries and industry. The keynote speakers, lecturers,
poster presentations and WGs meetings will contribute to spread the latest research works,
the exchange and development of new ideas and to build up collaborations between
laboratories and research activities.
On behalf of the COST Action FP0904 Management Committee I would like to thank
everybody that kindly contributed to the first Action FP0904 workshop: all the authors and
specially the keynote speakers, Holger Militz, Patrick Perré, Heiko Thoemen and Edo Kegel.
I gratefully acknowledge the help of the Scientific Advisory Committee in reviewing the
abstracts and preparing the scientific program.
I specially thank the Vice-Chairman of the Action, Dennis Jones, and Christelle GanneChédeville for their availability and help.
I express my sincere gratitude to the Action Grant Holder, Andreas Roth, and Nicole Cia and
Anicia Schneider for their help in preparing the book of abstracts and organizing the
workshop.
Parviz Navi
Chair of COST Action FP0904
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Workshop Organisation
Chair
Parviz Navi: Action Chair (Bern University of Applied Sciences, Switzerland)
Dennis Jones: Vice-Chair (Woodknowledge Wales, United Kingdom)
Scientific Advisory Committee
Mark Hughes: WG1 Leader (University of Alvar Aalto, Finland)
Mathieu Petrissans: WG1 Vice leader (University Nancy 2, France)
Lennart Salmen: WG2 Leader (Innventia Stockholm, Sweden)
Joseph Gril: WG2 Vice leader (University Montpellier 2, France)
Peer Haller : WG3 Leader (Technische Universität Dresden, Germany)
Christelle Ganne-Chedeville: WG3 Vice leader (Bern University of Applied Sciences, Switzerland)
Local Organiser
Andreas Roth
Workshop Venue
The workshop venue is Bern University of Applied Sciences Architecture, Wood and Civil Engineering ,
Solothurnstrasse 102, CH-2500 Biel
Main Building
Registration, information and the scientific program will take place in the Aula in the building C.
How to get to the Workshop venue:
By train
Various trains relate Geneva and Zürich international
airports to the Biel/Bienne railway station, which is
located in the city
centre: http://www.sbb.ch/en/index.htm
At the station Biel, take Bus No 1 "Eisbahn/patinoire".
Ride for 15 minutes. Get out at "Zollhaus", then walk
2 minutes in the direction of Solothurn.
With the car
Highway A5, Solothurn-Biel, direction Biel, Exit BielOst
Highway A6, Bern-Lyss, direction Biel, Exit Biel, then
head out for Bözingen.
Main road Neuchâtel-Biel, direction Bözingen.
Social Programme
Banquet: Thursday, February 17, 2011
The banquet will take place in the region of Biel. A bus service will be provided for all participants.
Please take your official invitation card with you !
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Tourist Information
Currency
The official currency in Switzerland are Swiss Franks (CHF) 1 Franken = 100 Rappen
The term Swiss Franks is usually abbreviated as CHF or Fr.
Voltage
Voltage: 230 Volts. The Plugs are Swiss-Type three-pin. A plug adaptor is necessary if incompatible
electronic gadgets are used
Foreign Exchange, Banks & Credit Cards
Money can be changed at the airport, at banks, Post offices and larger hotels
Business hours of banks:
Monday-Wednesday / Friday
Thursday
09:00-12:15 / 13:30-17:00
09:00-12:15 / 13:30-18:00
Post-Office Main Station Biel:
Monday- Friday
Saturday
07:30-18:30
08:00-16:00
Prices and Tips
Menu prices usually include service and taxes. In restaurants, a small tip is not expected, it shows the
appreciation to the waiter/waitress
Shopping
Typical shopping hours are :
Monday
Tuesday-Wednesday /Friday
Thursday
Saturday
14:00 – 18:30
08:00 – 18:30
08:00 – 21:00
09:00 – 17:00
Transportation
The best way to discover Biel is by public transport or by feet. The transport system is based on a
dense network of buses. The following tickets are available:
Single-ride ticket Zone S
CHF 2.80
24 hour (multiple ride) ticket
CHF 9.00
The tickets are available at the ticket machine at several bus stops or in every bus.
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Scientific
Program
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Wednesday February 16, 2011
08:00 - 08:40
Room
Aula
Registration at the Desk (Workshop place)
08:40 - 09:00
Aula
Opening Session
09:00 - 09:40
Keynote Session I (WG1)
09:00
Aula
Chairperson: Mark Hughes
Holger Militz , Michael Altgen: Development of methodology to predict wood
properties of thermally modified wood
09:40 - 10:20
p. 17
Aula
Session I – Chemical degradation of wood under Thermo-Hydrous treatments
(WG1)
09:40
Lennart Salmén, Yafang Yin: Chemical and micromechanical characterization
of softwood cell walls subjected to high temperature steaming
10:00
Wiesław Olek, Jan T. Bonarski, Ryszard Plenzler: Effects of changes in
hygroscopicity and ultrastructure on mechanical properties of thermally modified
wood
10:20 - 10:40
p. 19
p. 21
Aula
Session I - Poster presentations
Thomas Schnabel, Stefanie Wieland, Hermann Huber: Quality control of thermally
modified timber: An approach for in-line colour measurement method
p. 23
Stjepan Pervan, Vlatka Jirouš-Rajkovi, Josip Miklecic, Silvana Prekrat: Use of oils
in finishing of thermally modified wood for outdoor applications
p. 25
Pin Lv, Giana Almeida, José Otavio Brito, and Patrick Perré: Chemical mechanisms
of mild pyrolysis of poplar and spruce
p. 27
Charalampos Lykidis, Athanasios Grigoriou: Effect of a hydrothermal recovery process
on the acidity, chemical composition and formaldehyde emission of wood particles recovered
from laboratory and waste particleboards
p. 31
Melanie Wetzig, Tamás Hofmann, Tamás Rétfalvi, Tom Sieverts, Holger
Bergemann, Peter Niemz: Physical, mechanical and chemical properties of wood, heattreated with the vacuum-press-dewatering method
Jakub Sandak, Anna Sandak, Ottaviano Allegretti, Silvia Ferrari, Ignazia Cuccui,
Marco Fellin: Effect of wood treatment in low temperatures on the near infrared spectra
p. 35
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10:40 - 11:20
Room
Aula
Coffee Break and Poster Presentation
11:20 - 13:00
Aula
Session I continues
11:20
Mounir Chaouch, Mathieu Petrissans, Anélie Petrissans, Philippe
Gerardin: Prediction of durability for different softwood and hardwood species
heat-treated based on elemental composition analysis
p. 39
11:40
Tamás Hofmann, Melanie Wetzig, Tamás Rétfalvi, Tom Sieverts,
Holger Bergemann, Peter Niemz: The chemical properties of wood, heattreated with the vacuum-press-dewatering method
p. 41
12:00
Carmen-Mihaela Popescu, Maria-Cristina Popescu, Cornelia Vasile:
Spectral characterization of biodegraded and accelerated aging lime wood (Tilia
cordata Mill.)
p. 45
12:20
Giana Almeida, Diego V.B. Santos, Patrice Marchal and Patrick Perré:
Dimensional and gravimetric modifications occurring during heat treatment of fast
growing species
p. 47
12:40
Wim Willems, Holger Militz: Applicability of electron paramagnetic resonance
to characterize hygro-thermally modified wood
p. 49
13:00 - 14:20
Bistro
LUNCH
14:20 - 15:00
Keynote Session II
14:20
Aula
Chairperson: Lennart Salmén
Patrick Perré, Romain Remond and Giana Almeida: Modelling the coupled
mechanisms occurring when submitting wood to high temperature levels: a real
challenge
15:00 - 15:40
p. 51
Aula
Session II - Modelling of THM processing and predicting the behaviour of THM
(WG2)
15:00
Hamish Pearson, Brian Gabbitas, Sigurdur Ormarsson: Creep and
mechanosorption of wood at High Temperature
p. 55
15:20
Frederick A. Kamke and Josef Weissensteiner: Structural Composites
from VTC Wood
p. 59
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15:40 - 16:00
Room
Aula
Session II - Poster presentations
Saeed Abbasion, Dominique Derome, Jan Carmeliet: Modeling of heat and
mechanical effects during linear welding of wood
p. 61
Andreja Kutnar, Frederick A. Kamke: Comparison of non-linear transverse
compression strain of Douglas-fir and hybrid poplar under saturated steam
p. 65
Girma Kifetew, Jonaz Nilsson and Dick Sandberg: Is it possible to constrain moisture
movement of densified wood product mechanically?
p. 67
Patrick Perré and Romain Rémond: A comprehensive dual scale model applied to the
heat treatment of a whole stack of different boards
p. 69
Nicolas Henchoz, Lea Longis, Fred Girardet: Exploring the perspective of densified
wood through design
p. 71
Cedric Montero, Bruno Clair, Joseph Gril: Interaction between long term viscoelastic
and mechanosorptive response of wood
p. 73
Ernst Zürcher, Christian Rogenmoser: Time-dependent variations in hygroscopic
properties of solid wood of European spruce (Picea abies Karst.)
p. 75
16:00 - 16:40
Aula
16:40 - 18:40
Aula
Session II continues
16:40
Andreja Kutnar, Frederick A. Kamke: Transverse compression creep of
Douglas-fir in high temperature steam environments
p. 77
17:00
Ghonche Rassam, Behnam Jamnani: Densification of Wood in Iran- State of
the art
p. 79
17:20
Thomas Hecksher, Kirsi Läppanen, Jens Kai Holm, Ritva Serimaa,
Dorthe Posselt: Nanostructural and mechanical properties of green, torrefied
and welded softwood
p. 81
17:40
Julia Schreiber, Peer Haller, Uwe Hampel: Measurement of the Density
Distribution in Wood Using X-Ray Tomography
p. 85
18:00
Hamish Pearson, Brian Gabbitas, Sigurdur Ormarsson: Instantaneous
Wood Distortion under High Temperature Drying
p. 87
18:20
Michael Kaliske, Susanne Saft: Numerical Simulation of Wooden Structures
under Mechanical and Moisture Loading
p. 89
19:00 - 21:00
Core Group meeting
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Thursday February 17, 2011
08:30 - 09:10
Keynote Session III (WG3)
08:30
Room
Aula
Chairperson: Peer Haller
Heiko Thoemen: The thermo-hydro-mechanical behavior of wood during
composite manufacture
09:10 - 09:50
p. 91
Aula
Session III – New Products by THM-open System (WG3)
09:10
Chang-Hua Fang, Alain Cloutier, Pierre Blanchet, Ahmed Koubaa:
Densification of Wood Veneers with Heat and Steam Combined with Oil-Heat
Treatment
p. 93
09:30
Andreas Heiduschke, Peer Haller: The mechanical behaviour of formed
wood profiles
p. 95
09:50 - 10:10
Aula
Session III - Poster presentations
Kristiina Laine, Lauri Rautkari, Mark Hughes, Nick Laflin: Wood surface
densification by compression: Analysing the effect of process parameters
p. 97
Ulrich Schwarz, Alexander Pfriem: Technologies and manufacturing equipment for the
forming of solid wood
p. 99
Kévin Candelier, Mounir Chaouch, Philippe Gerardin, Mathieu Peterissans:
Mechanical properties of heat treated wood after thermodegradation under different
treatment intensity
p. 101
Jörg Wehsener, Peer Haller: Densified wood in 2- and 3 dimensional molding process
p. 103
Marek Grześkiewicz, Agnieszka Kurowska: Thermo-mechanically (TM) modified beech
wood (Fagus silvatica L.)as a raw material for parquet
p. 105
Jacek Wilkowski, Paweł Czarniak, Marek Grzeskiewicz: Machinability evaluation of
thermally modified wood using the Taguchi technique
p. 109
Misao Yokoyama, Joseph Gril, Miyuki Matsuo, Junji Sugiyama, Shuichi Kawai:
Mechanical characteristics of aged Hinoki
p. 113
10:10 - 10:50
Aula
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Room
Aula
10:50 - 12:30
Session III continues
10:50
Anna Dupleix, Rémy Marchal, Mark Hughes: Feasibility of wood peeling
process assisted by radiant energy.
p. 115
11:10
Martin Rhême, John Botsis, Joël Cugnoni, Parviz Navi: Fracture
mechanics characteristics of welded joint of wood
p. 117
11:30
Floran Pierre, Giana Almeida and Patrick Perré: An impact device
designed to assess the grindability of heat treated wood
p. 119
11:50
Julien Froidevaux, Thomas Volkmer, Joseph Gril, Marco Fioravanti,
Parviz Navi: Comparison between accelerated thermo-hydro aged wood and
naturally aged wood
p. 121
12:10
Miyuki Matsuo, Joseph Gril, Misao Yokoyama, Kenji Umemura,
Shuichi Kawai: Modelling of colour change induced by aging and heat treatment
by using the multi-process kinetic analysis
p. 123
12:40 - 14:00
Bistro
LUNCH
14:00 - 14:40
Keynote Session IV (WG1 + WG2 + WG3)
14:00
Aula
Chairperson: Dennis Jones
Edo Kegel and Dennis Jones: The development of commercial modified wood
processes – the Plato process
14:40 - 15:20
p. 125
Aula
Session IV Innovations and New Products laboratory and industrial scale
14:40
Lauri Rautkari, Mark Hughes: Wood surface densification using different
techniques
p. 127
15:00
Bernhard Stamm, Yves Weinand, Benjamin Hahn, G. Rossmaier:
Influence of the moisture content on the shear strength of welded wood-to-wood
connections
p. 131
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15:20 - 15:40
Room
Aula
Session IV - Poster presentations
Jussi Ruponen, Lauri Rautkari, Mark Hughes: Studies on self-bonded plywood
p. 135
Anne Lavalette, Régis Pommier, Patrick Castera, Michel Danis: Study of
impregnation of green wood by specific elastomer – Thermo-hydro-mechanical behavior of
wood/elastomer composite
p. 137
Agnieszka Kurowska, Piotr Borysiuk, Marcin Zbieć: Overheating process dynamics
of chipboard with addition of waste chips
p. 139
David Mannes, Eberhard Lehmann: Possibilities and limitations of advanced radiation
methods for imaging of wood
p. 141
Lars Blomqvist, Jimmy Johansson, Dick Sandberg: Contact free measurement of
complex shapes in the wood industry
p. 143
Stergios Adamopoulos, Tim Beaver, Takis Bouras: Properties of Microwave heated
wood and impregnated with natural oils
p. 145
15:40 - 16:20
Aula
16:20 - 18:00
Aula
Session IV continues
16:20
Lars Blomqvist, Jimmy Johansson, Dick Sandberg: Improving the
performance of bended laminated veneer products.
p. 147
16:40
Christian Welzbacher, Christian Brischke, Eckhard Melcher,
Karin Brandt, Andreas O. Rapp: Thermo-mechanical densification (TMD)
combined with an Oil-Heat-Treatment (OHT) of Norway spruce in laboratory and
industrial scale
p. 149
17:00
Róbert Németh, László Tolvaj, Sándor Molnár: Enhancing the quality of
high pressure steamed Robinia wood at industrial scale.
p. 151
17:20
Nadine Herold, Alexander Pfriem: Simultaneous shaping and fixation of
veneer by specific material modification
p. 153
17:40
Željko Gorišek, Aleš Straže: Comparative studies of sorption isotherms and
swelling behaviour of heat treatment and untreated hardwoods.
p. 155
from 19:30
BANQUET
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Friday February 18, 2011
Room
08:30 - 10:00
Working Groups
08:30
Working Group 1 meeting
SiZi C
08:30
C1.5
08:30
C0.10
10:00 - 10:30
Aula
Working Groups
10:00
General discussion of the Working Groups
10:45 – 12:15
Aula
Management Committee meeting
end of Meeting
Lunch
14
Bistro
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Abstracts
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Development of methodology to predict wood properties of thermally
modified wood
Holger Militz 1, Michael Altgen1
1
Department Wood Biology and Wood Products
University of Göttingen, Germany
[email protected]
Key words: Thermally modified wood, treatment processes, wood properties, quality control
Abstract
Thermal modification of wood is recognized as an environmental friendly technique to improve specific wood
properties without the use of chemical additives. Most thermal modification processes have in common the
treatment at temperatures between 160 and 260°C in an atmosphere with low oxygen content [1]. Various
thermal modification processes have been commercially implemented during recent years that provide for a
broad range of applications. Thermally modified wood shows constantly growing market shares with a
production volume in Europe of about 200.000 m³ [2]. In a first part of the presentation, different European
treatment processes will be reviewed.
Extensive research has been carried out to discover the arising changes in the chemical structure of the wood
[e.g. 3, 4, 5, 6]. Furthermore, it has been observed that some properties, especially dimensional stability and
natural durability, are improved with increasing treatment temperature and duration [7, 8]. Simultaneously,
some mechanical properties decrease due to an increased brittleness of the wood [9, 10]. Depending on the
application and its requirements it is therefore important to reach a compromise between improved durability
and dimensional stability on the one hand and decreased mechanical properties on the other hand. However,
besides temperature and duration other parameters, like the presence of residual water or oxygen as well as
elevated pressure during the process, also have an impact on the treatment intensity [11, 12, 13, 14, 15, 16]. As
a consequence, there is variation in the properties of thermally modified wood even if treatment temperature
and duration are identical.
Even with the existing production capacity in Europe, most of this wood is sold without certainty about its
inherent properties, since conventional test-methods are time- and labor-consuming. For this reason, the recent
scientific research work is focused on fast and reliable methods for industrial quality control utilization [e.g.
17, 18, 19, 20, 21].
In a second part of the presentation, different potential test-methods will be reviewed for their suitability in the
quality control of thermally modified wood. Different thermally modified wood species from a laboratoryscale process as well as from an industrial-scale process were used. In both cases, several treatment intensities
were applied. Natural durability and mechanical properties (bending strength, modulus of elasticity and impact
bending strength) were measured using conventional test-methods. Simultaneously, three potential testmethods for quality control based on EPR-spectroscopy, NIR-spectroscopy and HEMI (High-Energy-MultipleImpact) were applied to the same material. The aim of the study was to determine the treatment intensities with
the applied test-methods. Furthermore, interrelationships between the test-methods and the measured
properties were analyzed with respect to their suitability to estimate the properties of thermally modified wood.
Acknowledgement: Special thanks to PD Dr. Marina Bennati and Brigitta Angerstein from the Max Planck
Institute for Biophysical Chemistry for making available the EPR-spectrometer.
17
Cost-Action FP0904
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
18
Militz, H. (2002), Thermal treatment of wood: European processes and their background, IRG/WP
02-40241
EUWID (2009), Weitere Thermoholzanlagen wurden in Betrieb genommen, EUWID Holz special:
Bau & Innenausbau 2/2009: 80-82
Tjeerdsma, B. F., Boosntra, M., Pizzi, A., Tekely, P., Militz, H. (1998), Characterisation of thermally
modified wood: molecular reasons for wood performance improvement. Holz als Roh- und
Werkstoff, 56(3): 149-153
Kotilainen, R. A., Toivanen, T. J., Alén, R. J. (2000), FTIR monitoring of chemical changes in
softwood during heating, Journal of Wood Chemistry and Technology 20(3): 307-320
Tjeerdsma, B. F., Militz, H. (2005), Chemical changes in hydrothermal treated wood: FTIR analysis
of combined hydrothermal and dry heat-treated wood, Holz als Roh- und Werkstoff 63(2): 102-111
Boonstra, M. J., Tjeerdsma, B. (2006), Chemical analysis of heat treated softwoods, Holz als Rohund Werkstoff 64(3): 204-211
Kamdem, D. P., Pizzi, A., Jermannaud, A. (2002), Durability of heat-treated wood, Holz als Rohund Werkstoff 60(1): 1-6
Popper, R., Niemz, P., Eberle, G. (2005), Untersuchungen zum Sorptions- und Quellungs-verhalten
von thermisch behandeltem Holz, Holz als Roh- und Werkstoff 63 (2): 135-148
Boonstra, M. J., Van Acker, J., Tjeerdsma, B. F., Kegel, E. V. (2007), Strength properties of
thermally modified softwoods and ist relationship to polymeric structural wood constituents, Annals
of Forest Science 64(7): 679-690
Kubojima, Y., Okano, T., Ohta, M. (2000), Bending strength and toughness of heat-treated wood,
Journal of Wood Science 46(1): 8-15
Burmester, A. (1973), Einfluss einer Wärme-Druck-Behandlung halbtrockenen Holzes auf seine
Formbeständigkeit, Holz als Roh- und Werkstoff 31(6): 237-243
Giebeler, E. (1983), Dimensionsstabilisierung von Holz durch eine Feucht/Wärme/DruckBehandlung, Holz als Roh- und Werkstoff 41(5): 87-94
Mitchell, P. H. (1988), Irreversible property changes of small Loblolly pine specimens heated in air,
nitrogen, or oxygen, Wood and Fiber Science 20(3): 320-335
Wienhaus, O. (1999), Modifizierung des Holzes durch eine milde Pyrolyse – abgeleitet aus den
allgemeinen Prinzipien der Thermolyse des Holzes, Wissenschaftliche Zeitschrift der Technischen
Universität Dresden, 48(2): 17-22
Lenth, C. A., Kamke, F. A. (2001), Equilibrium moisture content of wood in high-temperature
pressurized environments, Wood and Fiber Science 33(1): 104-118
Mitsui, K., Takada, H., Sugiyama, M., Hasegawa, R. (2001): Changes in the properties of lightirradiated wood with heat-treatment, Holzforschung 55(6): 601-605
Johansson, D., Morén, T. (2006), The potential of colour measurement for strength prediction of
thermally treated wood, Holz als Roh- und Werkstoff 64(2): 104-110
Rapp, A. O., Brischke, C., Welzbacher, C. R. (2006), Interrelationship between the severity of heat
treatments and sieve fractions after impact ball milling: a mechanical test for quality control of
thermally modified wood, Holzforschung 60(1): 64-70
Welzbacher, C. R., Brischke, C., Rapp, A.O. (2009), Estimating the heat treatment intensity through
various properties of thermally modified timber (TMT), IRG/WP 09-40459
Bächle, H., Zimmer, B., Windeisen, E., Wegener G. (2010), Evaluation of thermally modified beech
and spruce wood and their properties by FT-NIR spectroscopy, Wood Science and Technology
44(3): 421-433
Willems, W., Tausch, A., Militz, H. (2010), Direct estimation of the durability of high pressure
steam modified wood by ESR-spectroscopy, IRG/WP 10-40508
Cost-Workshop
Chemical and micromechanical characterization of softwood cell walls
subjected to high temperature steaming.
Lennart Salmén1, 2, Yafang Yin2, 3
1Innventia, Box 5604, SE-114 86 Stockholm, Sweden
2Wallenberg Wood Science Center, Royal Institute of Technology, Stockholm, SE-10044, Sweden
[email protected]@innventia.com
2Wallenberg Wood Science Center, Royal Institute of Technology, Stockholm, SE-10044, Sweden
3Research Institute of Wood Industry, Chinese Academy of Forestry, Beijing 100091, China
email@[email protected]
Key words: glucomannan, imaging Fourier Transform Infrared (FT-IR) microscopy, lignin, moisture sorption,
nanoindentation, steam treatment, softwood, xylan
Abstract
Steam treatment, is a hygrothermal method of potential industrial significance to improve dimensional stability
and durability of wood materials. The steaming results in different chemical and micromechanical changes of
the nanostructured biocomposite comprising the wood cell walls.
In this study, spruce wood (Picea abies Karst.) subjected to high temperature steaming up to 180°C was
examined by imaging Fourier Transform Infrared (FT-IR) microscopy, illustrated in figure 1, and
nanoindentation to track changes in chemical structure and micromechanical properties of the secondary cell
wall. Similar changes of the chemical components due to steam treatment were found in both earlywood and
latewood. A progressive degradation of the carbonyl groups of the glucuronic acid unit of xylan and a loss of
mannose units of the glucomannan backbone, i.e. a degradation of glucomannan as well as a loss of the C=O
group linked to the aromatic skeleton in lignin was found. These changes decrease the accessible moisture
sorbing sites in the wood and may reduce linkage between the biopolymers in the cell wall. The changes were
mainly found for the steam treatment temperatures of 160 and 180°C, while no apparent decomposition of the
cell wall was noted at 140°C. These chemical changes may fully account for the changes observed regarding
hygroscopicity and elastic modulus of the wood material. Decreasing hardness for the 160 and 180°C-treated
samples is also consistent with hemicellulose degradation.
19
Cost-Action FP0904
Figure 1: Visible-light microscopy images of latewood (B). The white square box indicates the scanning area for IR
measurement; Corrected total full-spectral IR absorbance images of latewood. The small black box indicates typical pixel
positions corresponding to the secondary cell wall for measurement of cell wall spectra. Scale bar=50μm.
Acknowledgement: This study was sponsored by the Wallenberg Wood Science Center (WWSC) of the
Royal Institute of Technology (KTH) of Sweden. Yafang Yin gratefully acknowledges financial support by the
China Scholarship Council (CSC) and the Chinese National Natural Science Foundation (No.30972303), and
the approval of a short term scientific mission (STSM) by the COST (European Cooperation in the field of
Scientific and Technical Research) Action FP0802 for financial support of a visit to Max-Planck Institute of
Colloids and Interfaces for nanoindentation testing.
20
Cost-Workshop
Effects of changes in hygroscopicity and ultrastructure on mechanical
properties of thermally modified wood
Wiesław Olek1, Jan T. Bonarski2, Ryszard Plenzler3
1
Faculty of Wood Technology, Poznań University of Life Sciences,
ul. Wojska Polskiego 38/42, 60-627 Poznań, Poland
[email protected]
2
Institute of Metallurgy and Materials Science, Polish Academy of Sciences,
ul. Reymonta 25, 30-059 Kraków, Poland
[email protected]
3
Faculty of Wood Technology, Poznań University of Life Sciences,
ul. Wojska Polskiego 38/42, 60-627 Poznań, Poland
[email protected]
Key words: sorption isotherm, EMC, crystallographic texture, MOE, MOR, thermal treatment
Abstract
Thermal modification of wood is used to improve functional properties of the material. There is also a
common opinion that the improvement is accompanied by unwanted reduction of mechanical properties [1].
However, the reports on the influence of the thermal modification on the strength and brittleness of wood often
provided contradictory information [2]. In some studies it was reported that the average bending and tension
strength was reduced of ca. 10–30%. While, the results given for the thermally modified aspen wood depicted
slightly higher values of the modulus of elasticity and lower results for the modulus of rapture [3]. The
divergent data are usually not explained in a satisfying way. Moreover, the changes of the mechanical
properties are related neither to alteration of wood hygroscopic properties nor to ultrastructure.
The objective of the present study was to relate changes of the mechanical properties of wood after the thermal
modification to the alteration of the equilibrium moisture content (EMC) as well as crystallographic
organization of ultrastructure.
The thermal modification was made under laboratory conditions in atmosphere of moist air. Two wood species
were used in the study, i.e. poplar (Populus spp.) and European beech (Fagus sylvatica L.). The target
temperature of the modification was 220°C and it was kept for 60 min. The cooling phase was firstly done in
superheated steam and next in moist air only.
The sorption isotherms were determined for unmodified and modified wood. The experiments were made at
temperature of 24±1ºC for nine levels of the relative humidity controlled by salt solutions. The experimental
data of EMC were statistically analyzed for each option of the experiments and the relative humidity level. The
obtained sorption isotherms were parameterized with Hailwood-Horrobin and G.A.B. sorption models. Figure
1 presents an example of sorption isotherms (experimental data and fitted models) for adsorption and
desorption in beech wood (unmodified and modified at 220°C).
The space arrangement of the ultrastructure of unmodified and thermally modified wood of both species was
analyzed after performing the texture experiments. The X-ray diffraction method was used to register a set of
experimental pole figures. The three-dimensional texture function, i.e. the Orientation Distribution Function
(ODF) was calculated using the procedure implemented for materials of the monoclinic lattice symmetry. The
inverse pole figures were recalculated from the obtained ODF. The obtained skeleton profiles (i.e. intensity vs.
φ1 angle of Euler’s orientation space) of the ODF allowed determining changes of the dominating texture
components of unmodified and modified wood of both species.
The mechanical properties were determined for twin samples, which were obtained from modified and
unmodified wood. The modulus of elasticity (MOE) tests were made in the four-point bending on clean
21
Cost-Action FP0904
samples with dimensions of 20 · 20 · 300 mm. Tests for the modulus of rupture (MOR) were performed on the
same samples as the MOE tests and at the same type of beam loading. The compression strength (Rc) was
determined for samples with dimensions of 20 · 20 · 30 mm which were cut off from the ends of the elements
previously prepared for obtaining the bending samples. The number of the sample pairs was 18, 27 and 24 for
MOE, MOR and Rc, respectively.
The results of the sorption isotherms determination clearly showed that in service thermally modified wood
attained significantly lower moisture content as compared to unmodified wood stored in the same conditions,
i.e. same temperature and relative humidity. This seems to be a key factor explaining the observed apparent
increase of some mechanical properties after the thermal modification.
The performed analysis of the crystallographic texture showed that the wood ultrastructure was significantly
changed after the modification. The changes were identified in disappearing some previously oriented areas.
For instance, areas oriented in parallel to the {340} lattice planes were no longer observed in both species after
the thermal treatment. The observations were correlated with changes in MOE and MOR values after the
thermal modification.
30
unmodified
modified @ 220°C
25
EMC; %
20
15
10
5
0
0
20
40
60
80
100
H; %
Figure 1: Influence of the thermal modification on the reduction of equilibrium moisture content of beech wood.
Solid dots – desorption, empty dots – adsorption, Hailwood-Horrobin model fitted (solid lines)
Acknowledgement: The work was financially supported by the Ministry of Science and Higher Education as
the N N309 2876 3 research grant.
References
[1]
[2]
[3]
22
Hill, C.A.S., (2006), Wood modification: chemical, thermal and other processes. John Wiley,
Chichester.
Yildiz, S., Gezer, E.D., and Yildiz, U.C., (2006), Mechanical and chemical behavior of spruce wood
modified by heat, Building and Environment 41: 1762-1766.
Kocaefe, D., Chaudhry, B., Poncsak, S., Bouazara, M., and Pichette, A., (2007), Thermogravimetric
study of high temperature treatment of aspen: effect of treatment parameters on weight loss and
mechanical properties, Journal of Materials Science 42: 854-866.
Cost-Workshop
Quality control of thermally modified timber: An approach for in-line colour
measurement method
Thomas Schnabel 1, Stefanie Wieland1, Hermann Huber1
1
Markt 136a, 5431 Kuchl, Austria
[email protected]
Key words: Decrease in mass, colour measurement, in-line measurement
Introduction
Abstract
To meet the requirements of decision makers, it is important to develop validated national and international
standards as well as quality control systems for treated wood. A possible grading method is to divide the
grading system into two features, based on quality classifications. One distinguishing feature is represented by
the technical properties (e. g., antiswelling efficiency). The other feature is the aesthetic quality (e. g., colour)
of TMT. Such colour changes in solid wood during the thermal modification can be related to the treatment
intensity [1-4]. The wood colour in combination with other measurement categories formed the basis for
further investigations. The interaction between bending strength and the change in wood colour after the
modification process was investigated by Bektha and Niemz [2]. Bourgois et al. [5] explain the correlations
between the wood colour and the chemical composition during the heat treatment.
This investigation deals with an approach relating to the use of wood colour for in-line measurements for the
quality control of thermally modified timber.
Experimental
Norway spruce wood samples (30 x 30 x 30 mm³) were used for this investigation. The decrease in mass was
determined to express the influence of the heat treatment on the wood samples, and was calculated from the
oven-dried weight before and after the heat treatment (180°C and maximal 6 hours).
The wood colour was measured with the Mercury 2000 spectrophotometer (Datacolor) and the selected
diameter for the measurement was 11 mm.
The in-line measurement was performed with the GetSpec 2048-5-RM spectrometer (GetSpec.com) and the
fiber probe diameter was 6 mm. Also, the Vis-spectra were transformed to the CIE L*a*b* colour space.
Results and Discussion
On visible inspection, it was clear that the wood became darker. Also, analysis of the decrease in mass shows
that material properties were changed by the heat treatment [3]. Johansson and Morèn [6] mentioned the
sensitivity of the response of the L* values during the treatment. Therefore, it could be shown that the changes
in the L*value correlated well with the decrease in mass during thermal modification (cf. Fig. 1).
The tendencies of the changes in colour (e. g. L* value) of the two different methods (discontinuous and
continuous measurement system) presented comparable results. Therefore, in-line colour measurement method
seems a usable concept to measure the colour of the wood samples during the heat treatment.
23
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0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Figure 1: Correlation between the decrease in mass by air heat treatment and colour values (L*) for Norway spruce
Nevertheless, further studies are necessary to improve and optimize the in-line measurement method for the
application in heat treatment chambers. It is important to develop guidelines for quality assurance to save time
and money in industrial utilization.
References
[1]
[2]
[3]
[4]
[5]
[6]
24
Patzelt, M., Emsenhuber, G., Stingl, R., (2003) Colour measurements as means of quality control of
thermally treated wood. In: Proceedings of the 1st European Conference on Wood Modification, 3-4
April 2003, Ghent, Eds. Van Acker, J., Hill, C., Ghent University, Belgium. pp. 213-218
Bekhta, P., Niemz, P., (2003) Effect of high temperature on the change in color, dimensional stability
and mechanical properties of spruce. Holzforschung 57: 539-546
Brischke, C., Welzbacher, C.R., Brandt, K., Rapp, A.O., (2007) Quality control of thermally
modified timber: Interrelationship between heat treated intensities and CIE L*a*b* color data on
homogenized wood samples. Holzforschung 61: 19-22
Schnabel, T., Zimmer, B., Petutschnigg, A.J., Schönberger, S., (2007) An approach to classify
thermally modified hardwoods by color. Forest Products Journal 57:105-110
Bourgois, P.J., Janin, G., Guyounnet, R. (1991) The color measurement: A fast method to study and
to optimize the chemical transformations undergone in the thermally treated wood. Holzforschung
45: 377-382
Johansson, D., Morén, T., (2006) The potential of colour measurements for strength prediction of
thermally treated wood. Holz Roh Werkst 64:104-110
Cost-Workshop
Use of oils in finishing of thermally modified wood for outdoor applications
Stjepan Pervan1, Vlatka Jirouš-Rajković2, Josip Miklečić3, Silvana Prekrat4
1
Faculty of Forestry, Wood technology Department, University of Zagreb, Croatia
[email protected]
2
[email protected]
3
[email protected]
4
[email protected]
Key words: thermally modified wood, wood finishing oils, accelerated weathering, general appearance of the
surface, water permeability
Abstract
Thermally modified wood is increasingly used in outdoor conditions, but its surface also undergoes to
degradation by weathering as well as unmodified wood. Oils are largely used for protection of wood surface in
outdoor conditions because they are easy to maintain and recoat, and they enhance the appearance of wood
surface. The change of colour and gloss and surface cracking of thermally modified and unmodified wood
samples (oak (Quercus robur L.), ash (Fraxinus excelsior L.) and beech (Fagus silvatica L.).) were measured,
treated with three types of oils during the accelerated weathering in QUV device. The use of oils reduced
colour change of unmodified oak wood samples only in first hours of exposure (universal oil and teak oil up to
120 hours, and thermowood oil up to 180 hours) and for unmodified ash wood oils reduced colour changes
during the most of the exposure with the exception of ash samples finished with universal oil. On unmodified
beech wood samples universal oil reduced colour change up to 360 hours of exposure and teak oil and
thermowood oil during entire exposure. It should be mention that teak oil and thermowood oil change the
colour of unmodified wood to some degree because they contain pigments. Among three wood species of
unmodified and finished samples ash wood samples showed the most prominent change of colour after QUV
exposure. Colour change of thermally modified samples finished with teak oil and with thermowood oil was
smaller during entire exposure than colour change of unmodified samples and samples treated with universal
oil. The most prominent trend of colour change can be seen for thermally modified ash wood (at 190°C and
200°C) samples unfinished or finished with universal oil. Among unfinished thermally modified wood samples
the smaller colour change could be seen for oak and beech wood samples. At the end of exposure the colour
change of these samples was 1.7 smaller than colour change of ash wood samples. Oil treatment enhance gloss
of wood surface and highest gloss values were measured on thermally modified beech wood surfaces, and the
smallest were measured on ash wood surfaces thermally modified at 200°C. The gloss value of thermally
modified oak wood surface finished with teak oil was 12 time higher than gloss of unfinished thermally
modified oak wood; the gloss value of thermally modified ash wood surface (at 190°C ) finished with same oil
was 13 time higher than gloss of unfinished thermally modified ash wood, the gloss of thermally treated beech
wood treated with teak oil was 19 time higher than gloss of unfinished samples and the gloss of value of
thermally modified ash wood surface (at 200°C ) finished with same oil was 7 time higher than gloss of
unfinished thermally modified ash wood. A rapid decrease can also be seen in gloss of thermally modified oil
finished oak wood and ash wood samples during the first 26.5 hours of QUV exposure followed by small gloss
changes with continued exposure. During the first 26. 5 hours of QUV exposure marked gloss change of
25
Cost-Action FP0904
thermally modified beech wood samples is also evident followed by more intensive decrease in gloss values
compared to thermally modified oak and ash wood samples. The unfinished thermally modified samples
showed only small changes in gloss during QUV exposure. The permeability of liquid water and water-vapour
were also measured according to EN 927-5 and EN 927-4. Among all tested samples only thermally modified
samples of oak and ash wood at 190°C, finished with thermowood oil and ash wood samples thermally
modified at 200°C and finished with all three kinds of oils showed the value of liquid water permeability lower
than 175 g/m2 which is according to EN 927-2 limit value for coatings intended to use for dimensionally stable
wood products. Water-vapour absorption does not show such great deviations from values of unfinished wood
surfaces which means that the treated surfaces do not prevent water-vapour absorption and liquid water uptake
in the exposures to the high humidity for longer intervals (e.g. in autumn and winter months). All beech
samples exhibited the highest values of water vapour absorption with the exception of unmodified samples
treated with teak oil. Oils treatment reduced the cracking of the thermally modified samples. Teak oil and oil
for thermally modified wood offered similar protection to exposed thermally modified wood surfaces from the
effects of water and UV radiation, while the universal oil did not offer any protection from the colour change
of modified wood during exposure. Since the oil coating is also susceptible to photochemical degradation, for a
pleasant appearance of wood surfaces during outdoor use it is very important the timely refinishing in
accordance with the manufacturer's instructions. It can be concluded that colour changes of thermally modified
wood samples of all three wood species are reduced by teak oil and thermowood oil treatment during
accelerated weathering. Gloss changes are the most pronounced at the beginning of the exposure, and later
they are very small compared to the colour changes, for all wood species. All three species of thermally
modified wood samples showed a lower permeability of liquid water than the unmodified wood samples. The
lowest permeability of liquid water exhibited the samples treated with thermowood oil followed by teak oil,
and the highest permeability exhibited universal oil for all three wood species. Tested oils do not prevent the
absorption of large amount of water in the exposure to the high humidity for longer intervals. Untreated,
unmodified samples of all three wood species cracked less than untreated thermally modified samples during
accelerated weathering, and oil finishing of thermally modified samples decreased cracking. For a pleasant
appearance of oiled surface during outdoor use the regular maintenance according to the manufacturer’s
instructions is essential.
References
[1]
[2]
[3 ]
[4 ]
[5 ]
[6 ]
[7 ]
26
Bulian, F., Graystone, J.A., (2009), Wood coatings:Theory and practice. Elsevier, Amsterdam.
Feist, W.C., (2006), Finishing western red cedar decks.
http://www.wrcla.org/pdf/Finishing_WRC_Decks.pdf
Hägele, V., (2003), Öle und Wachse zur Oberflächenbehandlung von Holz. Landesverband Holz +
Kunstoff , Baden-Württemberg.
Gibson, S., (2007), Deck finishes. Professional Deck Builder • September/October 2007.
Hill, C.A.S., (2009), The potential for the use of modified wood products in the built. Proceedings of
the 11th International Conference on Non-conventional Materials and Technologies (NOCMAT
2009), 6-9 September 2009, Bath, UK.
Militz, H., (2002), Heat Treatment Technologies in Europe: Scientific Background and
Technological State-of-Art In: Proceedings of Conference on “Enhancing the durability of lumber
and engineered wood products” February 11-13, 2002,Kissimmee, Orlando. Forest Products Society,
Madison, US.
Williams, S.R.; Feist, W.C., (1993), Finishing Wood Decks. Wood design focus 4(3):17-20.
Cost-Workshop
Chemical mechanisms of mild pyrolysis of poplar and spruce
Pin Lv 1, Giana Almeida 1, José Otavio Brito 2 and Patrick Perré 1,
1
2
AgroParisTech, INRA, UMR1092, LERFoB, Wood Biomaterial Biomass Team, ENGREF,
14 rue Girardet F-54042 Nancy, France
[email protected]; [email protected]; [email protected]
USP (University of São Paulo), ESALQ (“Luiz de Queiroz” College of Agriculture), LQCE (Laboratory of
Chemistry, Cellulose and Energy), Piracicaba, Brazil
[email protected]
Key words: thermal treatment, thermogravimetry, gas analysis, model
Abstract
The motivation for this research arises from the usage of thermal treatment processes to transform woods into
various potential products. In order to enable the treated wood to acquire certain desired properties, such as
grindability or dimensional stability, but still preserving native properties such as energetic value or stiffness,
mild pyrolysis (treatment at temperature levels in the range 200-300°C) is a desirable preconditioning for
energy or material purposes. Poplar (Populus trichocarpa) and spruce (Picea abies) were selected as
representative species for hardwood and softwood in this study.
A thermogravimetric analyzer (Mettler Toledo STARe System TGA/DSC 1) was coupled to the Fourier
transform infrared spectrometer (Nicolet™ 6700) to investigate the mass loss of the samples and formation of
gas. For thermogravimetric experiments, a sample around 10 mg was program-heated from 25 to 280°C at a
heating rate of 5 °C/min under nitrogen with a gas flow of 50 ml/min. Simultaneously, when the sample was
heated, the evolving volatile products were flushed into the gas cell. The transfer line and gas cell were heated
to 280 °C and 290 °C respectively to avoid condensation on the cell wall. Infrared spectra over the range
4000–600 cm-1 were collected every 15 seconds at a resolution of 4 wavenumbers.
Thermogravimetry results (Fig. 1) reveal that it is possible to obtain different outcomes through duration or
temperature controlling, and prevent less wasteful in energy during thermal treatment. Furthermore, to
understand the chemical mechanism during the treatment, thermal decomposition gases were recorded in situ
though Fourier transform infrared spectrometer and the three-dimensional plot of the time-resolved spectra are
presented (Fig. 2). Moreover, the spectrum at the maximum weight loss rate of the sample was extracted for
chemical analysis (Fig. 3): bands at about 3500~3700cm-1, 2700~3000 cm-1, 1600~1800 cm-1, 1000~1600 cm-1
and around 750 cm-1are attributed to OH, C-H, C=O, aromatic skeleton and C-O absorptions. The appearance
of C=O absorption implies decomposition components of aldehydes and acids, while the O-H absorption
points to the occurrence of dehydration. Accordingly, the yields of gas products mainly are water, carbon
dioxide, formaldehyde, methanol, formic acid, acetic acid and phenol with the reference to the infrared
database.
27
Cost-Action FP0904
All the data from this research will be used to chose suitable degradation reactions and to determine the values
of parameters involved in the chemical formulation, including activation energy and heats of reaction. Such a
model, formulated at the micro-particle level, will be implemented in a computational model able to predict the
macroscopic behaviour [1]. This code will then be a useful tool to help the design of new reactors or the
control of existing plants. Other studies are also in progress in our lab on separate chemical components of
wood. If the interaction is found to be small, we could predict the behaviour of other wood species simply
from their chemical composition.
[1]
28
References
Rémond, R., Turner, I., Perré, P., (2010), Modeling the drying and heat treatment of lignocellulosic
biomass:
2D
effects
due
to
the
product
anisotropy,
Drying Technology Journal, 28: 1013 – 1022.
Cost-Workshop
100
0.00
-0.10
70
60
-0.15
50
-0.20
40
-0.25
30
20
0
500
1000
1500
Time (min)
a
2000
2500
100
0.2
90
0.0
80
-0.2
-0.4
70
-0.6
60
-0.8
50
-1.0
40
-1.2
30
20
-0.30
3000
DTG
Dimensionless mass (%)
-0.05
80
DTG
Dimensionless mass (%)
90
-1.4
0
500
1000
1500
2000
2500
3000
Time (min)
b
Figure 1: TG and DTG curves of (a) poplar; (b) spruce.
b
a
Figure 2: Three-dimensional plot of the time-resolved spectra for (a) poplar; (b) spruce.
b
99.4
99.2
99.9
99.1
99.8
99.0
99.7
98.9
99.6
98.8
99.5
98.7
99.4
98.6
99.3
98.5
99.2
%T
%T
99.3
98.4
99.0
98.2
98.9
98.1
98.8
98.0
98.7
97.9
98.6
97.8
a
99.1
98.3
4000
98.5
3500
3000
2500
2000
Wavenumbers (cm-1)
1500
1000
98.4
4000
3500
3000
2000
2500
Wavenumbers (cm-1)
1500
1000
Figure 3: Gas FTIR spectra at the maximum weight loss rate from (a) poplar; (b) spruce.
29
Cost-Action FP0904
30
Cost-Workshop
Effect of a hydrothermal recovery process on the acidity, chemical
composition and formaldehyde emission of wood particles recovered from
laboratory and waste particleboards
Charalampos Lykidis1, Athanasios Grigoriou2
1
Researcher
Aristotle University of Thessaloniki,
Faculty of Forestry and Natural Environment,
Laboratory of Forest Technology, 54124 - Box 243,
e-mail: [email protected]
2
Professor
Greece, Aristotle University of Thessaloniki,
Faculty of Forestry and Natural Environment,
Laboratory of Forest Technology, 54124 - Box 243,
E-mail: [email protected]
Key words: Hydrothermal treatment; particleboard; recovery; recycling; recovered particle properties
Abstract
The aim of the present paper was to study the effect of a hydrothermal recovery process on the acidity,
chemical composition and formaldehyde emission of wood particles recovered from laboratory and waste
particleboards. The hydrothermal treatments were carried out with saturated steam for 10min at a temperature
of 150°C, after water impregnating of the specimens. The utilized particles were οf two types: fresh wood
particles commercially used in particle board production and particles recovered from waste particleboards
collected by old furniture. The above particles were used for the production of laboratory particleboards and
were recovered again. This procedure was repeated twice for each particle type. It was found out that the
recovery procedure resulted in increased pH values as well as reduced formaldehyde emissions of both types
of used particles. In terms of chemical composition, it was found out that the ash content of the particles was
not significantly affected by the above procedure. On the other hand, lignin content was slightly reduced for
the fresh particles whilst did not show significant differences for recovered particles. Holocellulose content
was significantly reduced and the total extractives content seem to have increased due to the recovery
procedure for both types of particles used.
Acknowledgement: This paper is part of the 03ED928 research project, implemented within the framework of
the “Reinforcement Programme of Human Research Manpower” (PENED) and co-financed by National and
Community Funds (25% from the Greek Ministry of Development-General Secretariat of Research and
Technology and 75% from E.U.-European Social Fund).
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Cost-Action FP0904
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Cost-Workshop
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Wise L., Murphy M. and A. D’Addieco, (1946). Pap. Trade J. 122, No2
Yildiz S. and E. Gümüşkaya, (2006). The effects of thermal modification on crystalline structure of
cellulose in soft and hardwood. Build Environment 42, pp. 62–67
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34
Cost-Workshop
Physical, mechanical and chemical properties of wood, heat-treated with the
vacuum-press-dewatering method
Melanie Wetzig1, Tamás Hofmann2, Tamás Rétfalvi2, Tom Sieverts³,
Holger Bergemann3, Peter Niemz1
1
ETH Zürich, Institute for Building Materials, Wood Physics, Schafmattstrasse 6, 8093 Zurich, Switzerland
[email protected]
2
University of West Hungary, Institute of Chemistry, Faculty of Forestry, 9400 Sopron, Ady Endre u.5,
Hungary
[email protected]; [email protected]
³timura Holzmanufaktur GmbH, Am alten Stolberg 4, 06548 Rottleberode, Germany
[email protected]
Key words: bending strength, Brinell hardness, chemical properties, colour, density, heat treatment, moisture
content, thermal conductivity
Abstract
As a consequence of consumers’ growing ecological awareness, heat-treated wood gains in importance. With
thermal modification, the durability of wood can be enhanced even without any chemical preservatives.
Modern architectural projects often combine bright-toned walls and ceilings with trendy dark wooden elements
such as furniture or parquet floor.
In this study, hardwood samples were heat-treated on an industrial scale with the vacuum-press-dewatering
method (Vacu³), a process where apply the treatment temperature to the wood samples using heating plates.
The condensation water is exhausted during the entire treatment. The samples were modified by two different
intensities (medium (m) and high (h) process temperature). The degree of modification depends on the
modification process and intensity. The properties of a control (untreated wood samples) of the same charge
were also tested.
A variety of properties of beech, ash, poplar and oak samples were investigated. On the one hand, mechanical
properties such as density, bending strength, impact bending strength, MOE and Brinell hardness as well as
further physical properties (sorption capacity, colour) were measured on beech, ash and poplar. On the other
hand, chemical properties such as pH-value, release of acetic and formic acid and furfural were also measured
on beech and ash and in addition on oak.
The results of colour change investigations correlate with the used modification process and intensity. They
show that the samples darken with increasing treatment intensity.
Thermal modification also advantageously alters physical-mechanical as well as chemical parameters.
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Cost-Action FP0904
Table 1 summarises selected physical properties of the investigated samples. The density decreased as a
consequence of the heat treatment by beech (medium and high) and ash high samples and increased by ash
medium and poplar high. The equilibrium moisture decreased compared to the untreated samples. Bending
strength and impact bending strength decreased for all samples with exception of ash medium. Furthermore it
can be recognised that the treatment did not essentially affect the MOE with exception the ash medium. The
tangential Brinell hardness is increased in all samples of beech and poplar and ash medium. Ash high
decreased slightly.
Table 1: Physical properties of untreated wood samples and samples heat-treated by Vacu³: mean values and standard
deviations
Samples
Density
Moisture
Bending
Modulus of
Impact bending
Brinell hardness
content
strength
Elasticity
strength
tangential
[g/cm³]
[%]
[N/mm²]
[N/mm²]
[kJ/m²]
[N/mm²]
beech untreated 0.733 ±0.04 10.9 ±0.3 131.0 ±10.8 14852
±1542
103.7
±26.9
32.7
±3.7
medium 0.683 ±0.04
7.1 ±0.2 116.7 ±15.2 14069
±1150
62.3
±22.8
34.0
±7.7
high
0.676 ±0.04
5.7 ±0.3 106.0 ±23.6 14564
±1925
42.9
±27.0
35.0
±12.1
ash
untreated 0.574 ±0.08 10.6 ±0.6 83.7 ±27.0
9307
±3502
50.9
±25.0
25.7
±7.8
medium 0.636 ±0.05
6.5 ±0.6 111.2 ±23.0 13177
±2133
55.8
±20.3
30.7
±8.5
high
0.555 ±0.05
5.2 ±0.6 75.5 ±19.9
9835
±2239
30.3
±16.7
25.4
±7.7
poplar untreated 0.351 ±0.02 11.8 ±0.4 53.3
±6.2
7115
±805
27.8
±10.8
10.5
±2.0
high
0.365 ±0.07
5.2 ±0.3 58.0 ±13.0 8040 ±1745
19.6
±6.9
15.5
±2.9
Table 2 gives an overview of selected results of the chemical analysis. While the release of formic- and acetic
acid increased for beech and ash due to thermal treatment, oak shows reverse results. The furfural release
increased for the treated compared to the untreated samples against modification parameters (temperature,
time).
Table 2: Chemical properties of untreated wood samples and samples heat-treated by Vacu³: mean values and standard
deviations
Samples
pH value
Formic acid release
Acetic acid release
Furfural release
[-]
[mg/100g dry wood]
[mg/100g dry wood]
[mg/100g dry wood]
beech untreated
5.10
1.53
33.26
0.60
± 0.08
± 0.84
± 7.31
± 0.27
medium
4.86
2.19
53.44
4.84
±0.29
± 1.48
± 33.12
± 4.43
high
5.33
3.32
48.62
2.86
± 0.24
± 1.61
± 13.44
± 1.17
ash
untreated
5.57
1.44
6.43
Not detected
± 0.14
±0.84
±1.23
medium
4.88
4.89
94.25
4.61
± 0.22
± 2.61
± 58.07
± 2.26
high
5.36
3.43
60.21
2.52
± 0.18
± 1.59
± 26.41
± 1.41
oak
untreated
4.02
3.06
141.89
2.58
± 0.10
± 0.34
± 36.94
± 0.68
medium
4.39
2.76
75.57
27.36
± 0.08
± 0.31
± 32.34
± 8.28
high
4.78
2.58
27.32
7.35
± 0.11
± 0.42
± 8.34
± 0.74
As a conclusion, it can be said that changes of the properties come along with certain restrictions for the final
product. As a consequence of the deteriorated mechanical properties of the heat-treated compared to the
untreated samples, thermally modified wood cannot be used for load-bearing wood constructions. However,
new applications for heat-treated wood are evident. A main advantage is the reduced equilibrium moisture
content associated with better dimensional stability. Thus thermally modified wood can be used in areas where
humidity fluctuations occur. Possible applications are windows or parquet floors in bathrooms and kitchens.
Further tests to investigate the durability of wood heat treated by Vacu³ are still in progress. They will provide
further information about the effect resistance against fungal attack in dependence of the modified process
variables.
36
Cost-Workshop
Effect of wood treatment in low temperatures on the near infrared spectra
Jakub Sandak1, Anna Sandak2, Ottaviano Allegretti3, Silvia Ferrari4,
Ignazia Cuccui5, Marco Fellin6
IVALSA/CNR, via Biasi 75, 38010 San Michele All’Adige, Italy
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
Key words: low temperature wood treatment, NIR, 2D spectral correlation
Abstract
Introduction
The thermally modified wood has become a new commercial product having several advantages over the
natural wood. In consequence quite a lot of research has been conducted in order to understand changes to the
wood chemistry and wood structure exposed to elevated (150ºC – 250ºC) temperatures. Not much attention has
been however dedicated for such changes in moderate (50ºC – 150ºC) temperatures.
Recent developments in the fields of optics and electronics opened new possibilities for measurements of
various physical and chemical properties of materials. One of such techniques is near-infrared spectroscopy.
The method allows rapid and low cost assessment of the chemical composition of the surface by measuring
how the non-visible infrared light is absorbed by particular molecules. Fourier Transform Near Infrared
Spectroscopy (FT-NIR) is relatively new technique with a great potential for non-destructive measurement of
organic materials. Energy of infrared light stimulates to vibrations different molecule combinations (such as CH, -OH or -NH). Depending on the molecular structure, chemical composition or physical properties of the
measured surface can be straightforwardly scrutinized.
The goal of this research was to exploit the potential of the near infrared spectroscopy into evaluation of the
chemical changes to the wood exposed to moderate temperature thermal treatment.
Materials and methods
Three wood species: spruce (Picea abies), fir (Abies alba) and poplar (Populus sp.) were utilized as
experimental samples. Small blocks (40mm x 20mm x 5mm, length x width x thickness respectively) have
been cut out from the fresh wooden boards. It must be mentioned that such boards have not been dried or
anyhow thermally treated before tests. Experimental samples have been conditioned for three weeks in a
climatic chamber (20ºC, 65%RH) to unify the moisture distribution within blocks. The thermal treatment has
been performed in the laboratory oven, with the fresh air and normal pressure (1000hPa). The treatment
temperatures were 40 ºC to 100ºC with a step of 5ºC. The treatment time was 6 hours.
FT-NIR measurement has been performed on each block four times in different locations on the measured
surface, and an average of these measurements has been considered as a reference spectrum. Fourier transform
near infrared spectrometer VECTOR 22-N produced by Bruker Optics GmbH equipped with the fibre-optic
probe has been used for spectra collection. The spectral range measured was between 4000 cm-1 and 12000 cm1
. The spectral resolution of the spectrometer was set to 8 cm-1. Each spectrum has been computed as an
average of 25 successive scans in order to minimize the measurement error.
All the samples have been measured by NIR spectrometer before treatment, next day after treatment, one
month after treatment and three months after treatment.
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Cost-Action FP0904
For spectra pre-processing and data mining Opus 6.5 software package has been utilized. 2D spectral
correlation, Partial Least Squares (PLS) and Principal Component Analysis (PCA) have been applied for data
processing.
Results and conclusions
The wood exposed to moderate temperatures has been affected by the heat. The most significant variations to
the spectra can be visible on 2D correlation chart presented on Figure 1.
Figure 1. 2D synchronous correlation of the NIR spectra scanned from the spruce wood treated in moderate temperatures
It was also possible to predict the treatment temperature by applying Partial Least Square algorithm. As can be
seen on Figure 2, the thermally treated and non treated spectra were very well estimated.
Figure 2. Calibration chart of the treatment temperature prediction by FT-NIR for wood treated in moderate temperatures.
Acknowledgement: Part of this work has been conducted within a framework of project SWORFISH financed
by Provicia Autonoma di Trento
38
Cost-Workshop
Prediction of durability for different softwood and hardwood species heattreated based on elemental composition analysis
Mounir Chaouch*, Mathieu Petrissans, Anélie Petrissans,
Philippe Gerardin
*
Laboratoire d’Etudes et de Recherches sur le Matériau Bois, EA 4370 Université Henri Poincaré
Nancy 1, Faculté des Sciences et Technologies, BP 239, 54506 Vandœuvre-lès-Nancy, France
[email protected]
Key words: decay, durability, elemental composition, hardwood, heat treatment, thermo-degradation,
softwood
Abstract
Wood heat treatment is an attractive alternative to improve decay resistance of low natural durability wood
species. Decay resistance is strongly correlated to thermal degradations of wood cell wall components. Some
recent studies proposed the use of wood elemental composition as a valuable marker to predict final properties
of the material [1 and 2]. These results, initially obtained with pine, have been extended to different softwood
and hardwood species to check validity of the method using equipment specially conceived to measure mass
losses during thermal treatment. Heat treatment was performed on two softwood species (pine and Silver fir)
and three hardwood species (poplar, beech and ash) at 230°C under nitrogen for different times to reach mass
losses of 5, 10 and 15%. Heat treated specimens were exposed to fungal decay using the brown rot fungus
Poria placenta and the weight losses due to fungal degradation determined as well as initial wood elemental
composition. Correlations between weight losses recorded after fungal exposure and elemental composition
indicated that carbon content or O/C ratio can be used to predict wood durability conferred by heat treatment.
Moreover, it was observed that for given curing conditions thermo-degradation patterns of the different
samples differed considerably according to the wood species. The sole analysis of wood physical properties
like its density, thermal conductivity and diffusivity cannot allow explaining the observed differences, which
should also depend of thermally activated chemical processes depending of wood chemical composition.
References
[1]
[2]
Šušteršic, Ž., Mohareb, A., Chaouch, M., Pétrissans, M., Petrič, M. and Gérardin, P., (2009),
Prediction of decay resistance of heat treated wood on the basis of its elemental composition,
Polymer Degradation and Stability 95 : 94-97.
Nguila Inari, G., Pétrissans, M., Pétrissans, A., and Gérardin P., (2009), Elemental composition of
wood as a potential marker to evaluate heat treatment intensity, Polymer degradation and stability 94
: 365-368.
39
Cost-Action FP0904
40
Cost-Workshop
The chemical properties of wood, heat-treated with the vacuum-pressdewatering method
Tamás Hofmann1, Melanie Wetzig2, Tamás Rétfalvi1, Tom Sieverts³,
Holger Bergemann3, Peter Niemz2
1
University of West Hungary, Institute of Chemistry, Faculty of Forestry, 9400 Sopron, Bajcsy-Zsilinszky u 4,
Hungary
[email protected], [email protected]
2
ETH Zürich, Institute for Building Materials, Wood Physics, Schafmattstrasse 6, 8093 Zurich, Switzerland
³timura Holzmanufaktur GmbH, Am alten Stolberg 4, 06548 Rottleberode, Germany
[email protected]
Key words: VOC release, total phenol and soluble carbohydrate content, pH, heat treatment, condensation
water analysis
Abstract
With thermal modification, the durability of wood can be enhanced even without any chemical preservatives
extending its application fields markedly. This study focuses on the chemical investigation of hardwood (oak,
beech and ash) products, heat-treated in an industrial scale vacuum-press-dewatering (Vacu³) method and on
the evaluation of the parameters of condensation water exhausted during the treatment. The samples were
modified by a temperature over the range of 195 to 210°C, by two different intensities (medium (m) and high
(h) process temperature). The properties of untreated (u) wood samples of the same charge were also tested as
of reference.
The pH value, release of acetic acid, formic acid and furfural and also total phenol content was evaluated from
the wood samples giving hints at the specific degradation processes.
Waste water collected after the treatment of oak and ash and also water combined during 8 cycles of treatment
of different species were investigated for pH, conductivity, COD, VOC content, total phenol content and also
for main possible utilizable compounds using GC-MS and HPTLC techniques.
Release of VOC is a problem due health concerns. Results show though that the values for the measured
components were quite low compared to former results [1]. Proper treatment of waste water is a major problem
due to its acidity and high organic content. Its composition depends also on wood species, possible ways of
utilization need to be worked out in the future.
While the release of formic- and acetic acid increased for beech and ash due to thermal treatment, oak shows
reverse results (Table 1.). The furfural release increased for the treated (m) compared to the untreated (u)
samples. There is a slight decrease of VOCs while enhancing treatment from medium (m) to high (h), possibly
due to the effect of the vacuum depleting volatiles out of the wood. Total phenol content increases as an effect
of lignin cleavage: the greatest rise can be detected in case of beech which is the least heat stable of the woods,
while the decrease of the high initial values of phenolics in oak thru the treatment could possibly be attributed
to the heat degradation and vacuum-caused loss of the oak phenolics.
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Cost-Action FP0904
Table 1: Chemical parameters of the samples wood heat-treated by Vacu³: pH value, release of formic acid, acetic acid and
furfural, total phenol contents. Samples mean values ± standard deviations (n=6). nd.: not detected.
Samples
pH value
Formic acid
Acetic acid
Furfural
Total phenol cont.
[-]
[mg/100g d.w] [mg/100g d.w]
[mg/100g d.w]
[mmol/100g d.w]
beech
untreated 5.10 ± 0.08
1.53 ± 0.84
33.26 ± 7.31
0.60 ± 0.27
1.10 ± 0.12
ash
oak
medium
4.86 ± 0.29
2.19 ± 1.48
53.44 ± 33.12
4.84 ± 4.43
3.67 ± 0.87
high
5.33 ± 0.24
3.32 ± 1.61
48.62 ± 13.44
2.86 ± 1.17
5.08 ± 0.41
untreated
5.57 ± 0.14
1.44 ± 0.84
6.43 ±1.23
nd.
3.54 ± 0.84
medium
4.88 ± 0.22
4.89 ± 2.61
94.25 ± 58.07
4.61 ± 2.26
5.79 ± 1.49
high
5.36 ± 0.18
3.43 ± 1.59
60.21 ± 26.41
2.52 ± 1.41
6.32 ± 0.44
untreated
4.02 ± 0.10
3.06 ± 0.34
141.89 ± 36.9
2.58 ± 0.68
13.33 ± 5.72
medium
4.39 ± 0.08
2.76 ± 0.31
75.57 ± 32.34
27.36 ± 8.28
12.10 ± 1.72
high
4.78 ± 0.11
2.58 ± 0.42
27.32 ± 8.34
7.35 ± 0.74
9.63 ± 1.72
Table 2. summarizes the values of the waste water analysis. Parameters are strongly dependent on the species
treated. The high total phenol content of the waste waters confirms that during the treatment an efficient and
vacuum enhanced extraction takes place yielding high amounts of phenolic extractives in the waste waters,
especially in case of oak, where the high acidity (low pH) can also be attributed to the extraction of acetic acid
out of the wood. Combined extracts show almost neutral pH values, and low total phenolics, which depend on
the way of combination and treatment of individual wood extracts.
Samples
Ash
Oak
Combined
Table 2: Parameters of waste waters. (COD: Chemical oxygene demand)
COD
Conductivty
pH
Acidity
Total phenol cont.
[CO2 mg/liter]
[mS/cm]
[mmol NaOH/liter]
[mmol/liter]
97669
1.4
2.52
1.039
5.39 ± 0.06
234820
1.6
2.19
2.770
25.56 ± 0.45
89470
38.1
6.45
0.0198
3.28 ± 0.29
The high extract content of waste waters raises the possibility of proper utilization of these byproducts. For
these reasons complex chromatographic investigations have been carried out using GC-MS and HPTLC to find
out the major constituents of waste waters.
The major constituents of oak waste water and relative abundance (via peak area): Furfural (71%), acetic-acid
(16%), 5-methyl-furfural (5%), Homovanillyl-alcohol (1.3%), 5-Hydroxymethyl-furaldehyde (1%), vanillin
(0.58%), Whiskey-lactone (0.57%), 2,6-dimethoxy-phenol (0.48%).
The major constituents of ash waste water and relative abundance (via peak area): Acetic-acid (68%), 1hydroxy-2-propanone (11%), Furfural (6%), 5-methyl-furfural (3%), Formic-acid (2), 1-hydroxy-2-butanone
(1.5%), Butyrolactone (0.88%), 5-hydroxymethyl-furfural (0.6%)
The major constituents of combined waste water and relative abundance (via peak area): Furfural (85%), 5methyl-furfural (9%), Acetic-acid (1.7%), Guaiacol (1.3%), 1-hydroxy-2-propanone (1%), 2,6-dimethoxyphenol (0.45%), 2-methoxy-p-cresol (0.45%), Isoeugenol (0.28%)
The time course of the VOC release during storage of the wood products needs to be evaluated in the future for
quality control. Utilization fields for the valuable individual organic compounds (aldehydes, phenolics,
lactones and acids) found in the waste water need to be found or the utilization of the whole water mixture
needs to be solved.
42
Cost-Workshop
References
[1]
Hofmann, T., Rétfalvi, T., Albert, L., and Niemz, P., (2008), Investigation of the chemical changes in
the structure of wood thermally modified within a nitrogen atmosphere autoclave, Wood Research
53(3): 85-98.
43
Cost-Action FP0904
44
Cost-Workshop
Spectral characterization of biodegraded and accelerated aging lime wood
(Tilia cordata Mill.)
Carmen-Mihaela Popescu, Maria-Cristina Popescu, Cornelia Vasile
Romanian Academy “P. Poni” Institute of Macromolecular Chemistry,
Department of Physical Chemistry of Polymers, 41A Gr. Ghica Voda Alley, Ro.700487, Iasi, Romania,
[email protected], [email protected], [email protected]
Key words: lime wood, biodegradation, aging, IR spectroscopy
Abstract
Wood degradation is an essential process in the environment leading to the properties modification, recycles
complex organic matter and is an integral component of life [1-6].
The lime wood (Tilia cordata Mill.) samples were exposed to decay by Trichoderma viride Pers. and
Chaetomium globosum and to artificial ageing under temperature, humidity and UV light. Wood was exposed
to fungi for different durations up to 84 days, while under artificial ageing was exposed up to 600 hours. The
changes in wood structure have been investigated by FT-IR and 2D IR correlation spectroscopy.
When wood was exposed to soft rot fungi, the intensity of IR bands assigned to different vibrations from
cellulose and hemicelluloses show a decrease, while the intensities of the bands assigned to C–O vibrations
due to the formation of oxidized structures increase. At the same time, the intensity of the band assigned to C–
O in metoxyl groups from lignin shows a decrease with increasing exposure time. The differences between
reference and decayed wood spectra were examined in detail using 2D correlation spectroscopy and the second
derivative analysis. The formation of reactive species due to oxidation reactions induced by enzymes and the
demethoxylation of the lignin structure was evidenced.
The weathering behavior of lime wood is accompanied by chemical changes induced by exposure. It was
shown that the lignin is most sensitive component to the photodegradation processes as indicated by
considerable decreases in the intensities of the characteristic aromatic lignin band at 1505 cm−1 and other
associated bands. By 2D correlation spectroscopy has been demonstrated that the moment of C=O from
carboxyl and acetyl groups in hemicelluloses (xyloglucan) is changing first, followed by the C=C of aromatic
skeletal (lignin), C=O in non-conjugated ketones, carboxyl groups and lactones, absorbed O–H and conjugated
C–O groups in quinones. 2D correlation spectra generated from the exposure time dependent infrared spectra
of the studied decayed wood were obtained. The contour maps in the 1850–1485 cm−1 region were evaluated.
The positive correlation areas in the 2D spectra are given in white color, whereas negative correlation areas in
the 2D spectra are given in gray color.
In the synchronous 2D correlation IR spectrum (Figure 3a), four auto-peaks and six pairs of cross-peaks are
identified resulting that the band at 1737 cm−1 varies in the opposite direction to that of the other three bands
from 1664, 1604 and 1558 cm−1.
45
Cost-Action FP0904
a.
b.
-1
Figure 1. Synchronous (a) and asynchronous (b) 2D IRcorrelation spectra in the 1850-1485 cm region constructed from the
exposure time-dependent IR spectra (0-70 days)
The asynchronous 2D correlation spectrum constructed from the exposure time-dependent IR spectral
variations (Figure 3b) show five bands. The following sequence of the spectral intensity changes:
1737>1558>1664>1604, 1510 cm−1 was obtained. This sequence means that the moment of the C=O of acetyl
and carbonyl groups (hemicelluloses) is changing first, followed by C=C of substituted aromatic ring coupled
with conjugated C–O (lignin), and C=C of substituted aromatic ring (lignin).
It is known that, generally, soft-rot decay is characterized by the softening of the woody tissue surface.
Particularly, C. globosum is characterized by the specific action on carboxyl and acetyl groups in
hemicelluloses. This fungus attacks actively cellulose and hemicelluloses. Demethoxylation of lignin was
observed by decreasing the bands which are assigned to different vibrations of methoxyl groups in lignin.
Acknowledgement: The authors acknowledge the financial support from Romanian Academy and European
Social Fund - „Cristofor I. Simionescu" Postdoctoral Fellowship Program (ID POSDRU/89/1.5/S/55216) is
acknowledged.
References
[1]
[2].
[3]
[4]
[5]
[6]
46
Faix O., Bremer J., Schmidit O., Stevanovic T., Monitoring of chemical changes in white-rot
degraded beech wood by pyrolysis-gas chromatography and Fourier transform infrared spectroscopy,
J. Anal. Appl. Pyrol., 21, 147–162 (1993)
Korner I., Faix O., Wienhaus O., Attempts to determine the degradation of pine wood due to brown
rot with the aid of FTIR spectroscopy, Holz Roh Werkst., 50, 363–367 (1992)
Popescu M.-C., Contributions to optical characterization of some multicomponent polymeric blends.
PhD Thesis, Iasi, Romania (2009)
Noda I., Generalized two-dimensional correlation method applied to infrared, Raman, and other
types of spectroscopy, Appl. Spectrosc., 47, 1329–1336 (1993)
Dloula, J., Clair, B., Arnould, O., Horacek, P., and Gril, J., (2009), On the time temperature
equivalency in green wood : Characterisation of viscoelastic properties in longitudinal direction,
Holzforschung 63(3) : 327-333.
Popescu, C.-M., Popescu, M.-C., Vasile, C. Characterization of Fungal Degraded Lime Wood by FTIR and 2D IR Correlation Spectroscopy, Microchem. J., 95, 377-387 (2010)
Cost-Workshop
Dimensional and gravimetric modifications occurring during heat treatment
of fast growing species
Giana Almeida 1, Diego V.B. Santos 2, Patrice Marchal 1 and Patrick Perré 1
1
AgroParisTech, UMR1092, LERFoB, Wood Biomaterial Biomass Team, ENGREF, 14 rue Girardet F-54042
Nancy, France
2
USP (University of São Paulo), ESALQ (“Luiz de Queiroz” College of Agriculture), LQCE (Laboratory of
Chemistry, Cellulose and Energy), Piracicaba, Brazil
[email protected]
Key words: radial and tangential shrinkage, shrinkage anisotropy, mass loss, Rose gum, Caribbean pine
Abstract
Heat treatment of wood has been the subject of numerous studies in terms of chemical modifications.
However, the complexity of the wood structure, at both the ultra level and the anatomical pattern, gives rise to
a heterogeneous and anisotropic behavior, namely in terms of physical and mechanical properties. This domain
remains poorly known in spite of its importance during the process itself and for the product quality. Previous
works related the decrease of hygroscopicity and dimensional stabilization of the treated material [1,2].
Nevertheless, to our knowledge, the radial and tangential modifications occurring during the heat treatment
were never reported.
This study investigated the dimensional and gravimetric transformations occurred during heat treatment of two
fast growing species coming from commercial plantations in Brazil. Thus, radial and tangential samples of rose
gum (Eucalyptus grandis) and Caribbean pine (Pinus caribaea var. hondurensis) were subjected to dynamic
mechanical analysis (DMA) and themo-gravimetric analysis (TGA). In order to study the long-term process
degradation, DMA and TGA experiments were carried out at 220, 250 and 280oC (under nitrogen flow) with a
total residence time (treatment temperature) of 10 hours. DMA tests were performed on a TA Instruments®
DMA 2980 system in the creep mode using the tension film clamp. DMA tests were run in creep test mode at
different load levels. In this paper, only the tests with zero load force are reported, for which the displacement
sensor of the equipment indicates the free sample deformation. TGA tests were conducted on a
thermogravimetric analyzer (TGA/DSC 1 - Mettler Toledo® system).
Results showed that heat treatment induced significant dimensional variations (shrinkage) and that this
shrinkage increases with the treatment temperature (Figures 1 and 2). It is interesting to notice that the
shrinkage induced by heat treatment is anisotropic, tangential changes about twice the radial ones. This trend is
similar to the shrinkage caused in native wood by water removal in the hygroscopic domain. For example,
radial and tangential shrinkages for eucalyptus wood treated at 280°C were of 15.5 and 23.6 %, respectively.
In the case of pine wood, radial and tangential shrinkages of samples treated at 280°C were of 8.1 and 11.5 %,
respectively. Radial and tangential shrinkages presented different behaviors between species, where eucalyptus
exhibited a greater shrinkage than pine. Eucalyptus wood is denser than pine wood (average basic density of
430 kg/m3 for eucalyptus and of 390 kg/m3 for pine), the first presents a higher amount of cell wall substance
that can be degraded by heat. Previous works proved that the mass loss is an excellent parameter to synthesize
the intensity of heat treatment on wood properties [3, 4], Figures 1 and 2 corroborate these findings. Indeed,
these figures show a linear correlation between shrinkage and mass loss until about 20% of mass loss, and this
for both species. For pine, the behavior of this correlation was perfect, where shrinkage curves for the three
temperature levels in function of mass loss perfectly superposes. Heat treatment of wood is a very complex
47
Cost-Action FP0904
process due principally to the high variability of this material and the chemical reaction occurring during this
process. These difficulties can cause a large heterogeneity in the treated material. Results presented here can be
very useful for improving the quality of material obtained by this process.
16
Radial shrinkage (%)
14
12
Tangential shrinkage (%)
280°C
250°C
220°C
10
8
6
4
2
0
0
10 15 20 25 30 35 40 45 50 55 60 65
5
24
22
20
18
16
14
12
10
8
6
4
2
0
280°C
250°C
220°C
0
5
10 15 20 25 30 35 40 45 50 55 60 65
Mass loss (%)
Mass loss (%)
Figure 1. Radial and tangential shrinkages of rose gum in function of mass loss measured at three temperature levels.
12
280°C
250°C
220°C
8
Tangential shrinkage (%)
Radial shrinkage (%)
10
6
4
2
0
0
5
10
15
20
25
30
35
40
45
50
55
280°C
250°C
220°C
10
8
6
4
2
0
Mass loss (%)
0
5
10
15
20
25
30
35
40
45
50
55
Mass loss (%)
Figure 2. Radial and tangential shrinkages of Caribbean pine in function of mass loss measured at three temperature levels.
References
[1]
[2]
[3]
[4]
48
Brito, J.O., Garcia, J.N., Bortoletto Junior, G., Pessoa, A.M.C.,Silva, P.H.M. (2006) Densidade
básica e retratibilidade da madeira de Eucalyptus grandis, submetida a diferentes temperaturas de
termorretificaçã o. Cerne 12:182–188.
Almeida, G., Brito, J.O., Perré, P. 2009. Changes in wood-water relationship due to heat treatment
assessed using micro-samples of Eucalyptus. Holzforschung. 63(1): 80–88.
Almeida, G., Brito, J.O. Perré, P., 2010. Alterations of energy properties of eucalyptus wood and
bark subjected to torrefaction: The potential of mass loss as a synthetic indicator. Bioresource
Technology, 101 (24): 9778-9784.
Pierre, F., Almeida, G., Brito, J.O., Perré, P. 2010. Modifications of chemical and energy properties
of maritime pine and pedunculate oak subjected to torrefaction (submitted).
Cost-Workshop
Applicability of electron paramagnetic resonance to characterize hygrothermally modified wood.
Wim Willems 1,2, Holger Militz2
1
Firmolin Technologies, FirmoWood Nederland BV, Spoorstraat 3, 5975 RK Sevenum, The Netherlands
[email protected]
2
Wood Biology and Wood Products, Georg-August-University Göttingen, Büsgenweg 4, 37077 Göttingen,
Germany
[email protected]
Key words: Hygrothermally modified wood, Electron Paramagnetic Resonance, stable free radicals, redox
properties
Abstract
Thermo-oxidative treatments of wood result in an accumulation of immobile stable free radicals in the cell
wall matrix. Hygrothermal wood treatments generate such stable free radicals under dry as well as moist steam
conditions, as detected by Electron Paramagnetic Resonance (EPR) [1,2]. It has been shown in previous work
[1,3], that the specific stable free radical density in moist steam treated wood is a strong predictor for its
resistance against decay by Basidiomycetes, insensitive for tree variability and even tree species, within a
group of three softwoods and three hardwoods respectively. Various hardwood and softwood samples prepared
under varied process conditions, characterized by EPR and an antioxidant assay showed a single linear trend of
increased antioxidant capacity with increase of specific stable free radical density [3].
EPR has the potential to classify the durability of hygrothermally treated wood directly on small climate
conditioned samples, as produced, without reference to untreated matched samples. The general applicability
of EPR to characterize hygrothermally treated wood is discussed against questions regarding calibration,
sample preparation, and treatment process dependence.
References
[1]
[2]
[3]
Willems W., Tausch, A., Mentink, C., Militz, H. (2010) A persistent radical mechanism responsible
for the durability of heat treated wood, submitted to J.Wood Sci Tech
Sivonen, H., Maunu, S.L., Sundholm, F., Jämsa, S., and Viitaniemi, P. (2002) Magnetic resonance
studies of thermally modified wood. Holzforschung 56(6):648–654.
Willems W, Tausch A, Militz H (2010) Direct estimation of the durability of high-pressure steam
modified wood by ESR-spectroscopy. IRG/WP 10-40508: 1-9
49
Cost-Action FP0904
50
Cost-Workshop
Modelling the coupled mechanisms occurring when submitting wood to high
temperature levels: a real challenge
Patrick Perré, Romain Remond and Giana Almeida,
AgroParisTech, INRA, UMR1092, LERFoB, Wood Biomaterial Biomass Team, ENGREF, 14 rue Girardet F54042 Nancy, France
[email protected], [email protected], [email protected]
Key words: computational modelling, degradation reaction, heat treatment, high temperature drying,
multiphysics.
Abstract
When submitting a piece of wood to a flow of gas at high temperature, several coupled mechanisms take
places. Most of them are activated by the temperature level, but it is important to distinguish between
reversible activation and alteration activation. Roughly speaking the drying at high temperature (say up to
120°C) activates several reversible mechanisms[4] such as activation of bound water diffusion, decrease of the
liquid water viscosity, activation of viscoelastic properties, development of an internal overpressure due to
saturated water vapour pressure…
At higher temperature levels, permanent alterations occur. They take place at the macromolecular level of the
cell walls: degradation of hemicelluloses and condensation of lignins. Cellulose is considered to be quite
resilient to the effect of heat up to about 300°C.
Note that these temperature levels are to be understood as order of magnitude, as one has always to consider
the cumulated effects of temperature level and duration. Besides, many of these activated mechanisms,
reversible or not, are both hygro- and thermo-activated:
the glass transition zone of lignins is in the range 70°C-90°C when saturated and increases to c.a. 200°C when
dried,
for treatment durations of some hours, the thermal degradation of hemicelluloses is significant from about
200°C for dry wood, but starts at 100°C/120°C for saturated wood[3].
These chemical degradations induce dramatic changes in the properties of wood[1,2] such as hygroscopic
behaviour and shrinkage (Fig. 1), mechanical resilience, density, gross calorific value. Fig. 1 depicts some
examples of these changes.
Moisture content (%)
18
10
280°C nitrogen
250°C nitrogen
220°C nitrogen
220°C air
180°C air
untreated
Tangential shrinkage, βT (%)
21
15
12
9
6
3
20
40
60
Relative humidity (%)
80
100
E. saligna
8
untreated
6
180°C
4
2
0
220°CB
250°C 220°CA
280°C
0
10
20
30
40
50
Moisture content (%)
Fig. 1 - Hygroscopic behavior of heat treated Eucalyptus saligna wood. (A) Sorption curves. (B) Tangential shrinkage as a
function of moisture content (220°C A = 220°C air atmosphere; 220°C B = 220°C nitrogen atmosphere)[1].
51
Cost-Action FP0904
Based on a relevant formulation is derived for all these mechanisms, a multiphysics and multiscale
computation tool is able to simulate the wood behavior as a function of the process parameters (evolution of
the boundary conditions in time) [5,6,7].
Figure 2 depicts the simulation of the heat treatment of a whole stack of boards (20 boards 1.8 cm thick and 10
cm wide, hence 2.0 m of stack depth). During the drying and heating phase, the gas flow supplies heat to the
stack, namely for water evaporation, which explains the decrease of dry-bulb temperature along the stack. The
drying phase is not completed at the end of the plateau at 110°C. When the temperature increases above
110°C, a massive and sudden evaporation of the remaining water occurs, which gives rise to an important
pressure peak.
When the temperature level is enough to trigger the reactions, the reaction heats supplied to the board and the
volatiles produced by the reactions explains the temperature peak of the board and the second pressure peak.
The temperature peak of board n°1 attains 267°C. However, the simulation results highlight that the
exothermic reactions occurring in each single board can be accumulated along the stack: the temperature
overshoot of one board triggers more intensively the exothermic reactions of the next boards in the direction of
the gas flow. This explains why the temperature peak of board n°20 attains 295°C [5].
300
2.5
2.3
250
1.9
Board 1
150
1.7
Board 20
Oven T°
Pg 20
100
1.5
Relative pressure
Temperature (°C)
2.1
200
1.3
Pg 1
50
0
1.1
0
60
120
180
240
300
360
0.9
420
Time (min)
Fig. 2 - Evolution of temperature and relative pressure (Pg/Patm) at the surface and at core of the boards located at the stack
inlet (board n°1) and at the stack outlet (board n°20). Initial moisture content is 25%, and gasflow velocity 2m/s (From
Rémond et al. 2010).
References
[1]
[2]
[3]
[4]
[5]
52
Almeida, G., Brito, J.O., Perré, P. 2009. Changes in wood-water relationship due to heat treatment
assessed using micro-samples of Eucalyptus. Holzforschung. 63(1): 80–88.
Almeida, G., Brito, J.O. Perré, P., 2010. Alterations of energy properties of eucalyptus wood and
bark subjected to torrefaction: The potential of mass loss as a synthetic indicator. Bioresource
Technology, 101 (24): 9778-9784.
Placet V., Passard J., Perré P., 2008 - Viscoelastic properties of wood across the grain measured
under water-saturated conditions up to 135°C : evidence of thermal degradation, J. Mater. Sci., 43:
3210–3217.
Perré P. (Ed.), 2007 - Fundamentals of wood drying, 366 pages, COST E15 and ARBOLOR, Nancy.
Perré P., 2010 – Multiscale modelling of drying as a powerful extension of the macroscopic
approach: application to solid wood and biomass processing, Drying Technology, 28: 944-959.
Cost-Workshop
[6]
[7]
Rémond R., Turner I., Perré P., 2010. Dual-scale model for heat treatment of wood: evidence of
thermal run-away due to the cumulative effect of exothermic reactions, 17th International Drying
Symposium (IDS 2008), 1311-1316, Magdeburg, Germany.
Turner I., Rousset P., Rémond R., Perré P., 2010. An experimental and theoretical investigation of
the thermal treatment of wood in the range 200-260°C, Int. J. Heat Mass Transfer, 53:715-725.
53
Cost-Action FP0904
54
Cost-Workshop
Creep and Mechanosorption of Wood at High Temperature
H. Pearson1, B.L. Gabbitas2, S. Ormarsson3
1
Scion, Rotorua, New Zealand
[email protected]
2
School of Engineering, University of Waikato, New Zealand
[email protected]
3
Department of Civil Engineering, Technical University of Denmark, Denmark
[email protected]
Key words: Creep, mechanosorption, elevated temperature, radiata pine, thermo-sorptive-aging
Abstract
Creep and mechanosorptive behaviour of wood are two important phenomena that occur in wood during
thermo-hygro-mechanical processing such as drying or heat treatment. However, these variables are inherently
difficult to study and quantify experimentally due to equipment design difficulties and material behaviour
complexity. For example, for elevated temperatures, pressure rated equipment is required for humidities up to
100% and experimental design must account for any overlap between creep and mechanosorption at elevated
temperatures and moisture contents. A study is described in which the material properties of creep and
mechanosorption of radiata pine (Pinus radiata D.Don) were experimentally obtained and statistically
modelled as functions of temperature, moisture content and stress (Pearson et al 2004).
Tensile creep and mechanosorption displacement data was collected over time for tangential grain radiata pine
sapwood at temperatures between 70 and 150°C for a variety of moisture contents and applied stress. A full
description of three-dimensional mechanical behaviour for a single wood species is complex in that it requires
all combinations of tension, compression, and shear behaviour for the three grain directions, for heartwood and
sapwood, for all elements of the total strain equation and as functions of the main control variables
temperature, moisture content and stress. This study reduced as many of these variables as possible to focus on
equipment design and development and to keep experiments within achievable limits. Radiata pine was used
because it is an important plantation grown species in New Zealand.Sapwood was used because of the high
recovery rate, the tangential grain direction was chosen as it exhibits the greatest shrinkage range compared to
longitudinal and radial directions and tension testing was used as it avoids buckling failure and therefore yields
more uniform results. Matched samples were taken from one representative tree for which as much wood
quality information as possible was recorded. The wood quality information was then used as a covariate
during statistical analyses of the results. The use of samples from one tree instead of many also helped to
evaluate the efficiancy and accuracy of the equipment that was specially designed for this work.
55
Cost-Action FP0904
For the creep studies the moisture content was kept constant at varying levels but for the mechanosorption
studies the moisture content was varied cyclically. A modified central composite experimental design was used
for both the creep and mechanosorption studies to reduce the number of experiments. Wood moisture content
was controlled using a high temperature dew point sensor and a preliminary set of experiments was performed
to quantify the relationship between dew point, humidity and equilibrium moisture content whilst under
pressure. The results were then applied to the central composite design. The same levels of temperature were
used in both the creep and mechanosorption tests but applied stress was significantly reduced for the
mechanosorption tests compared to the creep tests in order to reduce the presence of creep.
Both creep and mechanosorption tests were performed in a modified Moldrup variable pressure kiln. Tensile
samples were connected to a specifically designed and constructed tensile rig that was able to accommodate
ten samples at a time. The rig included an external jack to enable either weight removal or application during
operation in order to control applied stress. The whole unit, including the Moldrup kiln was controlled through
a specifically developed control and data acquisition system called MechanoSpec.
As expected, creep results revealed a dramatic increase in creep strain for higher temperature, stress or
moisture content. Creep results were best described using a power law which interestingly indicated the lack of
a creep limit at higher temperatures. The amplitude response of the creep power law equation was found to be
primarily dependent on stress, temperature, moisture content and cycle number. Cycle number related to the
number of times a load was added or removed. Stress and temperature were best described by an exponential
term, which showed that the creep strain rapidly increased with an increase in either of these variables, whilst
MC was best described by a power term. The power term could be expressed as a linear function of stress.
Interestingly a small degree of morphing between the instantaneous elastic and creep curves was apparent at
higher temperatures. This was due to curvature in the elastic region for high, compared to low temperature
results. A greater displacement was statistically recorded for the first cycle of loading and unloading compared
to all succeeding cycles. This may have been due to irreversible plastic deformation but it is interesting to note
there may be a limit as later cycles usually reached the same level of displacement. The overall coefficient of
determination for the statistical creep equation was 0.740.
Mechanosorption displacement magnitude results were best described using a common low temperature
relationship where mechanosorptive displacement is a function of the absolute value of moisture change and
stress. The curvature to reach the mechanosorption displacement was modelled using an exponential function
containing temperature and mean moisture content terms. However, mechanosorption displacement was not
found to be dependent on temperature but the results revealed that an opposing phenomenon to
mechanosorption occurred due to reduced hygroscopicity. This was labelled as thermo-sorptive-aging and only
occurred when a change in moisture took place which was different to the change in moisture when drying
from green without adsorption. Thermo-sorptive-aging was a function of temperature and moisture content
oscillation cycle number and affected the final amplitude level of EMC, but not the rapidity to which the final
amplitude was reached. The cycle number was the number of times a moisture change had been effected
through a setpoint change and required some form of moisture content steady state to have been reached before
successive changes were made. The thermo-sorptive-aging effect was thought to be due to the loss of hydrogen
bonding sites in cellulose that occurred every time bound water and cellulose bonds were alternatively broken
and reformed through wetting and rewetting. It is likely such a phenomenon could be used to reduce drying
times and internal checking through some sort of bond shuffling, where wood structure is massaged during
oscillatory drying. This would theoretically allow as much of the wood structure as possible to be gently
morphed into a modified form without placing excessive stress on the remaining original crystallite bound
water bonds that occur when drying without adsorption. The overall coefficient of determination for the
statistical creep equation was 0.880.
56
Cost-Workshop
Acknowledgement: Scion, Rotorua, New Zealand for the provision of experimental facilities and the New
Zealand Government for funding this research.
References
[1]
Pearson, H., Gabbitas, B., Ormarsson, S., Pickering, K., (2004), Design of an investigative
programme to model creep and mechanosorption of radiata pine at high temperatures, Proceedings of
the Third International Conference of the European Society for Wood Mechanics, September 6-8,
Vila Real, Portugal, 103-111.
57
Cost-Action FP0904
58
Cost-Workshop
Structural Composites from VTC Wood
Frederick A. Kamke1 and Josef Weissensteiner2
1
Professor, Dept. Wood Science & Engineering, Oregon State University, Corvallis, Oregon USA
[email protected]
2
Graduate Research Assistant, Dept. Wood Science & Engineering, Oregon State University, Corvallis,
Oregon USA
[email protected]
Key words: THM, densification, adhesive bonding
Abstract
VTC wood is produced by mechanical compression perpendicular to the grain under conditions of dynamic
steam pressure and temperature. The purpose is to permanently increase the density and thus enhance strength,
stiffness, and hardness. The high density VTC lamina may be used for structural composite manufacture, or for
other applications where hardness, strength, or stiffness are important. The VTC process is experimental.
Commercial implementation will require knowledge concerning the operational window of the VTC process.
Since the VTC process is a dynamic process, time is a critical parameter in each stage of manufacturing. It has
also been recognized that VTC wood requires less adhesive than normal wood. The reduction in adhesive
consumption will have a major influence on the cost of manufacturing a laminated composite from VTC wood.
This study investigated processing time and adhesive consumption in the manufacture of a laminated VTC
composite.
Figure 1: VTC device in Green Building Materials Laboratory at Oregon State University
59
Cost-Action FP0904
The manufacturing parameters examined were time of steam exposure prior to compression, rate of
compression, compression time, and amount of adhesive used. The target degree of densification and
temperature of saturated steam were constant for all processes.Rotary-peeled hybrid poplar (Populus sp.)
veneer was used. Testing included measurements of density and modulus of elasticity before and after VTC
processing. Parallel laminated composites were then produced using phenol-formaldehyde adhesive. The
laminated composites were then tested to failure using 3-point bending as well as a bondline shear test. Total
VTC processing time varied from 10 to 20 minutes.
Acknowledgement: Funding provided by Oregon BEST and USDA Wood Utilization Center
60
Cost-Workshop
Modeling of heat and mechanical effects during linear welding of wood
Saeed Abbasion1, Dominique Derome1, Jan Carmeliet2
1
Wood Laboratory, EMPA, Dübendorf, Switzerland
[email protected]
2
Chair of Building Physics, ETH Zürich and Laboratory for Building Science and Technology,
EMPA, Zürich, Switzerland
[email protected]
Key words: Linear wood welding, Thermo-mechanical Analysis, Temperature dependent properties
Abstract
Friction welding of wood is a solid-state joining process. The welding process involves the relative motion of
the two wood pieces, under pressure normal to the welded plane. During the process, the joint interface heats
up, inducing plastic deformation and partial chemical degradation. Heat is generated by material deformation
(plastic deformation) and friction. The bonding interface that results from friction welding presents a
densification and some physical and chemical transformations, whereby entangled wood fibers are drowned
into a matrix of softened and partly reticulated wood intercellular material, such as lignin and hemicelluloses.
In this study a coupled heat-poromechanical model [1] is developed and numerically solved using the finite
elements method. Due to the symmetry in the linear vibration welding and for the aim of simplicity, a two
dimensional analysis of one of two pieces is presented. In a similar manner as what has been done in modeling
of metal welding [2], the actual frictional movement is not modeled and a heat source plane is introduced at the
interface, see Fig. 1.
Heat Flux
y
P2
P1
Air
X
Pressure
(a)
(b)
Figure 1: (a) Schematic representation of the geometry and boundary conditions (b) Temperature field at t = 4.5s and MC =
12%
61
Cost-Action FP0904
70
70
60
60
von Mises stress (MPa)
von Mises stress (MPa)
The work against the surface is equal to the velocity multiplied by the normal pressure and the friction
coefficient. The heat conduction equation (Fourier’s law) is solved to obtain the temperature distribution in the
wood as a function of time. The thermal boundary conditions include convection with the environment and
heat flow at the interface. The amount of heat flow at the interface for several welding time has been measured
with infrared thermography at the side of the two wood pieces during welding by Ganne-Chédeville et al [3]
and we use this data as input for our analysis. Due to the low thermal conductivity of wood and high heat
generation rate between the two wood pieces, there is a sharp temperature gradient in a narrow band near the
interface
with
temperature
going
from
room
temperature
up
to
250°C.
The
dependencies of the mechanical and thermal properties of the wood on the temperature have to be
appropriately taken into account. Using existing data from literature for thermal conductivity and specific heat
[4] as a function of temperature (and moisture content) and data related to elastic properties, such as elastic
stiffness, plastic behavior, etc [5], a first analysis of the numerical results reveals that the thermo-elastic fields
in the wood specimens are significantly influenced by temperature dependencies of wood properties. Figure 2
shows that not taking into account temperature dependence can lead to important variations in von Mises
stress.
50
40
30
20
40
MC = 0% (P1)
MC = 12% (constant properties P1)
MC = 12% (P2)
MC = 0% (P2)
MC = 12% (constant properties P2)
30
20
10
10
0
0
50
MC = 12% (P1)
5
Time (sec)
10
(a) Time response at the points P1 and P2
0
0
0.01
0.005
Position (m) (Y - coordinate)
0.015
Stress along the lines parallel to the y axis which
containing points P1 and P2 at t = 4.5s
Figure 2: von Mises stress for different moisture contents and material properties
In parallel to acquire a complete set of material properties and a consistent set of well-defined conditions
during welding, the modeling efforts are now aiming at including mass transport resulting from the sharp
temperature gradient and at predicting the densification of wood at the weld line. Progress in these respects
will also be presented.
62
Cost-Workshop
Acknowledgement: This project is supported by SNF Sinergia Grant no. 127467.
References
[1]
[2]
[3]
[4]
[5]
Coussy, O., (2004), Poromechanics. Wiley, Chichester
Lindgren, L.-E., (2001) Finite element modeling and simulation of welding Part 1 Increased
Complexity. J. Thermal Stresses, 24: 141-192.
Ganne-Chédeville C., Duchanois G., Pizzi A., Leban J.-M., Pichelin F., (2008c), Predicting the
thermal behavior of wood during linear welding using the finite element method, J.Adhesion
Sci.Technol., 22: 1209-1221.
Olek1 W., Weres J., Guzenda1 R., (2003), Effects of Thermal Conductivity Data on Accuracy of
Modeling Heat Transfer in Wood, Holzforschung, 57: 317- 325
Popovic Z., Soskic B., Miric M., (2007), Effect of hydrothermal treatment on some mechanical
properties of Beachwood, Prerada drveta, Jul-September
63
Cost-Action FP0904
64
Cost-Workshop
Comparison of non-linear transverse compression strain of Douglas-fir and
hybrid poplar under saturated steam
Andreja Kutnar1, Frederick A. Kamke2
1
University of Primorska, Primorska Institute for Natural Sciences and Technology, Muzejski trg 2, 6000
Koper; ILTRA d.o.o., Celovska cesta 268, 1000 Ljubljana, Slovenia
[email protected]
2
Oregon State University, Department of Wood Science and Engineering, 119 Richardson Hall, Corvallis,
Oregon, USA
[email protected]
Key words: Cell wall modulus, densification, non-linear strain function, relative density
Abstract
The transverse compression behavior of Douglas-fir wood (Pseudotsuga menziesii) and hybrid poplar (Populus
deltoides × Populus trichocarpa) at high temperature (170°C) and under saturated steam condition was
studied. The compression process and equipment were described in detail by Kamke and Kutnar
[1].Transverse compressive loading under saturated steam at 170°C followed a typical stress-strain curve of
wood. The linear elastic, collapse, and densification regions were observed (Figure 1). The compressive
modulus of hybrid poplar, 5.7 MPa [1] was lower than Douglas-fir, 7.5 MPa. Lower compressive modulus of
hybrid poplar could be expected due to lower initial relative density. Furthermore, the hybrid poplar wood used
in the study was all tension wood, which contained a well defined gelatinous (G) layer in the longitudinal
fibers. One characteristic of the G-layer is a low microfibril angle, which would contribute to a low transverse
compression modulus. Furthermore, lower relative density of hybrid poplar resulted in higher compressive
strains.
6
5
Stress [MPa]
4
3
2
1
0
0
0.1
0.2
Douglas-fir
0.3
Strain
0.4
0.5
0.6
0.7
Hybrid poplar
Figure 1: Comparison of average stress-strain curves of Douglas-fir and hybrid poplar wood in transverse compression under
saturated steam at 170°C.
65
Cost-Action FP0904
The yield stress of Douglas-fir specimens was higher then yield stress of hybrid poplar specimens, while
densification stress of both wood species was the same. The densification strain agrees with the 0.55 value
reported by Wolcott [2], while the yield strain was somewhat higher than the value of 0.03 expected for wood
in this density range with an initial thickness of 6 mm.
The non-linear strain function was obtained from the average stress-strain response (Figure 2). The comparison
of the non-linear strain function of Douglas-fir specimens and hybrid poplar specimens compressed under the
same saturated steam conditions revealed significant differences. This result supports the assumption that the
non-linear strain function accounts for differences of cellular structure. At strains higher then 0.1 the non-linear
strain function of hybrid poplar wood deviated from non-linear strain function of Douglas-fir wood. With
increasing strain the difference in strain function increased. The difference is assumed to be due to different
cellular structure of softwoods versus hardwoods. Lower initial relative density of the hybrid poplar allowed
larger compression strain compared to the higher initial density Douglas-fir.
3.5
Non-linear strain function
3
2.5
2
1.5
1
0.5
0
0
0.1
0.2
0.3
Strain
0.4
0.5
0.6
0.7
Hybrid poplar
Douglas-fir
Figure 2: Comparison of non-linear strain function φ(ε) for Douglas-fir wood and hybrid poplar in transverse compression
under saturated steam at 170°C.
Different cellular structures of hardwoods versus softwoods likely caused different behavior of the non-linear
strain function. Heterogeneity of the cellular structure of wood likely influenced the calculation of cell wall
modulus using a theory of cellular foams to model wood in transverse compression. However, when
comparison is made on the basis of relative density change the transverse compression behavior of Douglas-fir
and hybrid poplar were remarkably similar.
Acknowledgement: The project was supported by the National Research Initiative of the USDA Cooperative
State Research, Education and Extension Service, grant number 2006-35504-17444 and USDA Wood
Utilization Research Center Special Grant number 2008-34158-19302.
References
[1]
[2]
66
Kamke, F.A., Kutnar, A., 2010: Transverse compression behavior of wood in saturated steam at 150
to 170°C. Wood and Fiber Science 42(3): 1-11
Wolcott, M.P., 1989: Modeling viscoelastic cellular materials for the pressing of wood composites.
PhD Dissertation. Virginia Tech, Blacksburg, Virginia, 182 pp.
Cost-Workshop
Is it possible to constrain moisture movement of densified wood product
mechanically?
Girma Kifetew, Jonaz Nilsson and Dick Sandberg
Linnæus University
School of Engineering
SE-351 95 VÄXJÖ
[email protected]
[email protected]
[email protected]
Key words: densification, shape stability, EWP,
Abstract
A modified softwood product would enable utilization of softwood in areas, where today fails to accomplish.
Densification is one of the oldest wood modification methods that have been used to improve some wood
properties. Compressing wood in the transverse direction will reduce the void volume of the lumens in the
wood material and increase its density. This process is commonly called densification. Already in 1886, the
idea of densifying wood by compressing it in the radial direction was understood [1]. Hence, this study
presents an attempt made in developing a novel wood composite product for use in structural applications. The
aim of wood densification is to compress solid wood product without causing “damage” in the cell walls. The
goal is to improve wood properties desired for specific applications like hardness and abrasion resistance. One
of the major problems with densified wood however is the ability of the product to retain its original dimension
under the influence of moisture.
There have been many studies relating to stabilization of moisture movement of densified wood by using
various treatments. This includes chemical treatments as well as heat and steaming processes.
To prevent the formed wood from returning to its initial form, the following procedures are available: 1)
Chemical modification by de-activation of the OH-sites by acetylation (substitution of the -OH by CH3COOgroups), or formaldehydation (fixing of H2CO between two hydroxyls to obtain a strong chemical bond), etc.
2) Thermo-Hydro-Mechanical treatment, i.e. the use of temperature, moisture and mechanical action. 3)
Hydrolysis of hemicelluloses under the effect of water and high temperature in order to relax the internal
stresses. 4) Mechanical fixing by gluing, nailing, screwing, etc. [2].
However, the chemical methods that have been used (1-3 above) have also some drawbacks. Therefore, the
principal goal of this study was to investigate the effect of mechanically moisture movement stabilization
method.
This study primarily utilizes a simple solid wood densification method. The technique is based on compressing
a clear solid softwood piece with vertical annual rings in the radial direction by restraining the tangential
expansion. Further, three-layered cross laminated composite product was manufactured by utilizing the
densified wood as a service layer. Moreover, the service layer maintains a harmonious pattern and emphasises
the esthetical property of the modified product.
In order to manufacture a 3-layered cross laminated composite; 4 mm thick densified wood panels with a size
of 500 by 500 mm2 were prepared. These panels were used as the service layer of the cross laminated
composite. The unmodified middle and bottom layer panels were also prepared of radially sawn wood without
defects such as knots. Thus, the cross laminated composite consists of 4 mm thick densified service layer and 6
mm thick middle layer. However, the bottom layer was prepared with three different thicknesses i.e. 2 mm, 4
mm and 6 mm. As a result, three groups of modified cross laminated composite with four samples in each
group were manufactured. Finally, a total of 12 square shaped cross laminated samples with a size of 500 by
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Cost-Action FP0904
500 mm2 were manufactured and examined. The adhesive used for gluing piece together in to panels was
polyvinyl acetate (PVAc). While, for manufacturing of the laminated composites polyurethane glue was used.
Finally, the cross laminated composite was subjected to climate variations in order to investigate the shape
stability. For that reason, an extensive cupping data of the cross laminated composite were collected during a
period one year at varying relative humidity conditions, Figure. As a result, the influence of service to bottom
layer thickness ratio on the degree of moisture induced cupping is remarkably noticeable. Moreover, an
appreciable shape stability of the cross laminated composite is recorded by increasing the service to bottom
layer thickness ratio and when the service to bottom layer thickness ratio was about 2 the 3-layered cross
laminated composite was form-stable.
Figure 1: Setup of cupping measurement on the service layer of the 3-layered cross laminated composite.
The result of this study reveals the significance of service to bottom layer thickness ratio on the shape stability
of the cross laminated composite. Consequently, the performance and the shape stability of the cross laminated
composite were significant when the service to bottom layer thickness ratio increases. Therefore, it appears
feasible to disclose the appreciable degree of shape stability, hardness and wear resistance of the product.
Accordingly, cross laminated composite can be considered as one of the promising mechanical methods for
improving moisture movement of densified wood product. It will also in some cases make it possible to
modify softwood products without chemical or thermal treatments.
References
[1]
[2]
68
Vorreiter, L. (1949). Holztechnologisches Handbuch, Band I. (Wood technology handbook, volume
1.) Verlag George Fromme & Co., Wien.
Navi, P. & Sandberg, D. (2011). Introduction to thermo-hydro-mechanical (THM) wood processing.
Presses polytechniques et universitaires romandes, Lausanne
Cost-Workshop
A comprehensive dual scale model applied to the heat treatment of a whole
stack of different boards
Patrick Perré and Romain Rémond,
1
AgroParisTech, UMR1092, LERFoB, Wood Biomaterial Biomass Team, ENGREF,
14 rue Girardet F-54042 Nancy, France
[email protected]
[email protected]
Key words: pyrolysis, wood, variability, thermal run-away, simulation
Abstract
The heat treatment of wood under inert atmosphere at temperature levels ranging from 200°C to 300°C (mild
pyrolysis) is an alternative to the use of chemicals for the preservation of solid wood. Indeed, due to a thermal
degradation of the cell wall components, a mild pyrolysis significantly changes the material properties, which
results in better durability and stability than natural wood. However, industrial plants have to overcome serious
problems due to exothermic reactions, to obtain a homogeneous final product quality, both within boards
(core/surface) and within stack (inlet/outlet). To address these problems at a fundamental level, a dual-scale
computational model is used here in which both scales (board and stack) are computed simultaneously:
At the local scale, the heat and mass transfers and the degradation reactions are formulated and solved by a
multiphysics computational model known as TransPore (The 2-D version is used in the present work) [1,2].
The boundary conditions to be used for each board come from the stack scale.
At the global scale, the energy and mass balances of the airflow are written for each channel formed by two
adjacent board layers. The solution at this upper scale requires the heat and mass fluxes exchanged which each
board to be computed by one module of TransPore [3,4].
Simulations were performed to understand certain industrial situations, for which a thermal runaway may
occur. The stack is composed of layers with 20 beech boards with the following dimensions: 1.8×10×250 cm3
dimensions (hence, 2.5 m long for the air channel). The stickers are 1.8 cm thick and the gas velocity is 3 m/s.
The initial moisture content of our reference test is equal to 10%.
In order to emphasize the stack effect regarding the exothermic reactions, the first simulation (Fig. 1a) is
performed with identical beech boards. The dramatic heterogeneity of heat treatment observed (core
temperature peak attaining 259°C and 280°C respectively for the inlet and outlet boards) results from the dual
scale coupling:
at the local scale, an overheating of the board, namely in the core, due to the exothermic reactions,
at the global scale, a thermal runaway along the airflow generated by the heat supplied from boards to gas.
The second simulations (Fig. 1b) included the wood variability through its density, gaseous permeability and
initial moisture content, each one assumed to obey a Gaussian law tuned to represent the tree variability.
Boards with higher initial moisture content have a longer drying time, which turns in a delayed heat treatment
phase. As a consequence, the heat treatment starts when the gas temperature already increased. This leads to a
sudden heat treatment phase, which is worse for the process heterogeneity.
In order to try to limit the effect of the board location, the air flow is periodically reversed each five minutes in
the third configuration (Fig. 1c). In this case, the core temperature of all boards attained a peak at about 275°C,
but the risk of thermal run away still exist.
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The last configuration tested is computed with a larger gas velocity, 7m/s, which increases the efficiency of the
heat exchange between the airflow and the boards and reduces the NUT along the stack (Number of Unit
Transfer). By this way, the thermal runaway can be avoided to a large extend (Fig.1d).
Board 20
2.4
150
Pg 20
2.1
Oven T°
1.8
100
3.3
3.0
200
2.7
2.4
150
2.1
Oven T°
100
1.8
1.5
50
0
60
120
180
240
Pg 1
1.2
300
0.9
420
360
1.5
50
0
1.2
0
60
120
Time (min)
3.3
2.7
200
2.4
150
2.1
Oven T°
1.8
100
1.5
50
0
1.2
0
60
120
180
240
300
360
0.9
420
240
300
360
3.6
3.0
2.7
200
2.4
150
2.1
Oven T°
1.8
100
1.5
50
0
0.9
420
3.3
250
3.0
Temperature (°C)
Temperature (°C)
250
180
Time (min)
b)300
3.6
300
Relative pressure
a)
Relative pressure
2.7
Temperature (°C)
Board 1
200
3.6
250
3.0
Relative pressure
Temperature (°C)
250
0
300
3.3
Relative pressure
3.6
300
1.2
0
60
120
180
240
300
360
0.9
420
Time (min)
Time (min)
d)
c) 1: Evolution of temperature and the relative pressure (Pg/Patm) at the core of the boards. (a) identical properties for all
Figure
boards, (b) simulation including variability, (c) air flow periodically reversed each 5 minutes, (d) a larger gas velocity 7m/s.
References
[1]
[2]
[3]
[4]
70
Perré, P. and Turner, I., (1999), A 3D version of TransPore : A Comprehensive Heat and Mass
Transfer Computational Model for Simulating the Drying of Porous Media, Int. J. of Heat and Mass
Transfer, 42: 4501-4521.
Turner, I.W., Rousset, P., Rémond, R., Perré, P., (2010), An experimental and theoretical
investigation of the thermal treatment of wood in the range 200-260°C, Int. J. Heat Mass Transfer,
53: 715-725.
Perré, P. and Rémond, R., (2006), A dual scale computational model of kiln wood drying including
single board and stack level simulation, Drying Technology Journal, 24: 1069-1074.
Rémond, R., Turner, I., Perré, P., (2010), Dual-scale model for heat treatment of wood: Evidence of
thermal run-away due to the cumulative effect of exothermic reactions, 17th International Drying
Symposium (IDS), Magdeburg, Germany: 1311-1316
Cost-Workshop
Exploring the perspective of densified wood through design.
Nicolas Henchoz1, Lea Longis2, Fred Girardet3
1
EPFL+ECAL Lab, 11, rue du 24 janiver, 1020 Renens, Switzerland
[email protected]
2
ENSCI, 48 rue St Sabin, 75011 Paris, France
[email protected]
3
Rino, Ruelle de Belle-Maison 14 1807 Blonay, Switzerland
[email protected]
Key words: Densified wood, densification, design, shape, scaling, material science, moulding, thermo-hydromechanical treatments, THM, EPFL+ECAL Lab
Abstract
The EPFL+ECAL Lab is using design methods to explore the potential of densified wood. The research is
based on work done at EPFL by Parviz Navi’s team [1] and technological developments made by Fred
Girardet [2]. The objective of these explorations is to provide new applications for densified wood and to
generate novel results by using an original approach to the material. The EPFL+ECAL Lab is currently
collaborating with Yves Weinand, head of the IBOIS (EPFL), and Parviz Navi from the University of Applied
Sciences, Bern.
Fig. 1: Formal exploration of densified wood: rough surface, wave shape and complex geometry along with the initial pieces
of wood.
Initial results in design and technology have been obtained from this exploration, which was initiated in 2010.
EPFL’s experimental wood densifying installation has been modified to permit the densification of larger
pieces and study the possibilities for using and shaping them. The method of formal research by design was
used to push the material to its limits and explore expressive capacities. This led to the creation of a modular
molding system that has enabled us to do a large range of geometrical, tactile, functional and esthetic
investigations.
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Cost-Action FP0904
The mould system consists of six modules, 3 for the female moulds and 3 for the male mould, which can be
contained in a 24 cm x 8 cm x 12cm volume (the latter dimension corresponds to the axis of compression).
Each module of the mould has an 8x8 cm surface of compression to test geometries, surface characteristics and
the esthetic impact. Experiments were done using spruce, which has a high densification potential. The
treatment phases include a deformation and then a densification of the wood (fig.1). The post-treatment phase,
which serves to completely stabilize the sample, was not validated in this first experimental phase.
The resulting pieces highlight the formal potential of wood, with large deformations running parallel and
perpendicular to the fibers, and with a radius of curvature less than 0.61 cm, even for densified thicknesses
greater than 1 cm. The tests gave an indication of the potential this process has to create complex shapes while
at the same time exposing the esthetic aspects of the densified material. The curvature of the moulds is
reflected in the slice of wood; the densified fibers are exposed and their relationship to the mechanical
properties, and thus the functionality of the object, is evident. Pieces made with different levels of constraint
show the variation in color that results from varying degrees of densification. In the many experiments that
were carried out, it became evident that wood has a large capacity to reproduce the surface characteristics of
the mould, conferring textures to the objects and giving a tactile dimension to a specific procedure used. This
formal exploration of densified wood is contributing to establishing the first creative principles for the use of
this material by designers, such as: the possibility of orienting the deformations in all the directions
perpendicular to the axis of compression, taking advantage of the surface characteristics of the mould, using
the visual expression of the densified fibers.
On the technological front, experiments enabled us to show that the principles of densification remained
applicable at a larger scale. The surface of compression of the pieces was enlarged from 4x4 cm to 24x8 cm,
resulting in densified thicknesses between 0.2 and 4 cm.
An introduction of geometrical perturbations perpendicular and parallel to the fibers did not result in
significant changes in the densification procedure.
Because the molding system only has openings at the end of the longest dimension (24cm), one can deduce
that the vapor transfer that controls the plastification and homogeneous hardening processes can take place
despite a relatively large distance. Tests were systematically conducted with the fibers oriented in the direction
of the mould openings to encourage gas transfer.
Regulating atmospheric pressure and humidity during the process was found to be fundamentally important for
achieving a homogeneous densification and obtaining stable pieces that would not swell or crack after removal
from the mould.
In conclusion, densified wood has the potential for a vast array of applications. Visual and tactile
characteristics complement the macroscopic mechanical and formal capacities of this material. These qualities
must be accompanied by an improved understanding of the transfer phenomena occurring in the wood, to
guarantee the reproducibility of the procedure and its compatibility with industrial processes.
References
[1]
[2]
72
Parviz Navi, Frédéric Heger (2005), Comportement thermo-hydromécanique du bois, PPUR,
Lausanne
Heger F.et al., (2003), Shape stabilisation of densified wood through THM post treatment with a new
multiparameter reactor, 2th International Conference of ESWM, Stockholm, p. 193-198.
Cost-Workshop
Interaction between long term viscoelastic and mechanosorptive response of
wood
Cedric Montero1a, Bruno Clair1, Joseph Gril1
1
Laboratoire de Mécanique et Génie Civil, Université Montpellier 2 – CNRS
cc048, Place Eugène Bataillon, 34095 Montpellier Cedex 5, FRANCE
a
[email protected]
Key words: clear wood, viscoelasticity, mechanosorption
Abstract
Since the first-published work in the 50’s the time dependent behaviour raised an increasing interest in wood
material research. Creep research has a decisive influence in timber structures where prediction of total
deflection is necessary for durable structural design.
The nature of polymeric constituents induces viscoelastic behavior to wood. In constant environment the
representation of creep against logarithm of time could be composed of two straight-line parts joined by a
curved transition [1]. Such a linear description of kinetic suggests an infinite strain level in long-term
prediction. However as a semi-crystalline polymer wood is expected to tend toward a limit of creep level. A
simplified rheological approach using parabolic models has been proposed by Huet [2] to model timedependent behavior of wood in longitudinal direction.
Sorption processes are suspected to accelerate time by increasing compliance [3]. This phenomenon called
mechanosorptive effect interacts with ongoing time-dependent evolution and induces a slope decrease after a
cycle in the logarithm description [4].
Matched spruce specimens (L=100 x R=10 x T=2mm) have been submitted to four-point bending creep test
(inner span = 40 mm and outer span = 80 mm) in controlled climatic environment. The strain has been
measured on lower and upper surface of each specimen using electric gages. Four specimens were loaded at
high humidity level (w ≈ 27%) below the limit of linearity of viscoelastic and mechanosorptive response [5].
Two specimens were kept unloaded for free swelling and shrinkage determination. Three specimens were
weighted occasionally for moisture content determination w.
Parabolic models have been used to estimate creep limit of the viscoelastic description. Submitted to sorption
cycles (from w ≈ 27% to w ≈ 7%) the increase of compliance and the decrease of slope evolution have been
observed. Comparison between viscoelastic evolution and mechanosorptive increment during a sorption cycle
seems to support the hypothesis that mechanosorptive can induce an apparent time-lag but also a non
recoverable strain.
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References
[1]
[2]
[3]
[4]
[5]
74
Hunt, D. G., (2004, The prediction of long-time viscoelastic creep from short-time data
Wood science and technology, 38/7, 479-492
Huet,
C.
Quelques
aspects
du
comportement
thermo-hygro-viscoelastique
Cabinet C. Huet, (1988)
Grossman, P. Requirements for a model that exhibits mechano-sorptive behaviour
Wood science and technology, (1976), 10/3, 163-168
Hanhijärvi, A. and Hunt, D. (1998) Experimental indication of interaction between viscoelastic and
mechano-sorptive creep. Wood Sci. Technol. 32(1):57-70
Hunt, D. G. Linearity and non-linearity in mechano-sorptive creep of softwood in compression and
bending Wood science and technology, (1989), 23/4, 323-333
Cost-Workshop
Time-dependent variations in hygroscopic properties of solid wood of
European spruce (Picea abies Karst.)
Ernst Zürcher1 , Christian Rogenmoser2
1
Bern University of Applied Sciences BFH
Architecture, Wood and Civil Engineering AHB
Solothurnstrasse 102
CH-2500 Biel 6, SWITZERLAND
[email protected]
2
[email protected]
Key words: Wood properties, Seasonal variations, Moon phases, Drying, Water sorption
Abstract
Scope and methodology
Traditional knowledge, in form of so-called rural rules, indicates that the date of tree felling has an important
influence on wood quality. The main factor, after the season of the year, is said to be the position of the moon.
The objective of the presented project was to study the variability of some user-related properties of wood, by
analyzing measurable parameters. The material stems from four different Swiss sites and is representative of
central European conditions. This part of the study involved 576 trees — Norway Spruce (Picea abies Karst.)
and Sweet Chestnut (Castanea sativa Mill.) — felled on 48 dates throughout the fall and spring of 2003–2004
(always on Mondays or Thursdays). Before the start of the experiment, one sample was taken on the same day
from each of the tested trees, to serve as reference. Wood properties analyzed are: Water Loss, Shrinkage
under controlled drying, air dry and oven dry density. Relative Density is calculated as ratio dry density / fresh
density. Smaller series of samples were tested on hygroscopicity (water sorption).
Main Results
The statistical analysis of the complete data series reveals (in addition to a seasonal trend) a generally weak,
but highly significant role of the synodic and of the sidereal moon cycles, to a lesser extent of the tropical
cycle. If the synodic lunar month (4 quarters) is subdivided in 8 segments of about 3.5 days each (“syn1” to
“syn 8”; “syn 1” beginning with the New Moon NM, “syn 5” beginning with the Full Moon FM), one of the
strongest “jumps” is occurring around FM, from “syn 4” to “syn 5”. The main publication [1] shows the
corresponding variability for the feature “Water Loss”, representative for the drying behaviour. A same type of
lunar-correlated variations is observed for the values of Relative Density. On the variation curve for the 48
successive felling dates, it appears that the lunar-related differences are more marked for the central 4 months
of the trial.
Water loss
The cause for the variations in Relative Density lies in similarly fluctuating values in the loss of free and bound
water during the controlled drying process, but in an opposite sense. Here too, marked differences around Full
Moons occur in the central winter months only. A comparison of the obtained values around FM during this
period indicates a mean drop in Water Loss of 4.5% (shortly after FM being compared with shortly before
FM).
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Cost-Action FP0904
Water sorption
One of the most important physical properties of wood, decisive for weathering behaviour and for decay
resistance, is its hygroscopicity. One of the two test methods chosen for estimating the variations in
hygroscopicity was to expose one face of the samples to direct contact with water, 5 mm being immersed for 9
minutes. The capillar ascent of water was estimated by calculation of the relative weight increase. Fig. 1 shows
the variations of Water Sorption by capillarity for samples obtained from 24 weeks of tree collection. Both the
limitation of the “lunar effect” on the 4 central months and the systematic drop directly after FM are very
similar to what was observed on Water Loss . A noticeable fact is that for capillarity, the mean amplitude of
this decrease (25.9%) is much more pronounced. These tests were made with independent sample series.
Figure 1: Variation curve of capillar Water Sorption of sapwood samples of Spruce from Château d’Oex. Legend of fellings
around Full Moon: O = fellings in the 3.5 days before FM / O = fellings in the 3.5 days after FM. Each point represents
12 values (here without std.dev.).
Interpretation and perspectives
This illustrates the importance of the wood-water interface, which obviously undergoes seasonal and lunarcorrelated reversible changes. The results from this study bring some objectivity into a mainly unexplored field
of traditional knowledge, a field subject to controversial discussions. Further research in chronobiology of
wood could lead to an ecological technique enhancing some specific wood properties.
Acknowledgements: This research was supported by funds provided by Wolfermann-Nägeli-Foundation
Zürich, Chambre des Bois de l’Ouest Vaudois, Sezione Forestale Cantonale (Ticino), Federlegno Ticino,
Graubünden Holz (Amt für Wald Mittelbünden), Kantonsforstamt Schwyz, Schwyzer Arbeitsgemeinschaft
HOLZ, Kloster Einsiedeln SZ and Thoma Holz GmbH (Austria). The realization occurred with the
collaboration of Dr. Thomas Volkmer, Werner Gerber, Andrea Florinett, Christian Barandun, Eric Treboux,
Denis Pidoux, Serge Lüthi, Christophe Rémy, Daniel Meyer, Marco Delucchi, Theo Weber, Dr. Joan Davis.
Reference
[1]
76
Zürcher, E., Schlaepfer, R., Conedera, M., Giudici, F.. (2010). Looking for differences in wood
properties as a function of the felling date: lunar phase-correlated variations in the drying behavior of
Norway Spruce (Picea abies Karst.) and Sweet Chestnut (Castanea sativa Mill.). Trees.(2010) 24: 3141
Cost-Workshop
Transverse compression creep of Douglas-fir in high temperature steam
environments
Andreja Kutnar1, Frederick A. Kamke2
1
University of Primorska, Primorska Institute for Natural Sciences and Technology, Muzejski trg 2, 6000
Koper; ILTRA d.o.o., Celovska cesta 268, 1000 Ljubljana, Slovenia
[email protected]
2
Oregon State University, Department of Wood Science and Engineering, 119 Richardson Hall, Corvallis,
Oregon, USA
[email protected]
Key words: compressive deformation, creep, densification,
Abstract
The literature is lacking an adequate description of the complex rheological behavior of wood during wood
densification. Therefore, the aim of the research was to examine the time-dependent behavior of Douglas-fir
(Pseudotsuga menziesii) wood with varying regimes of temperature and moisture exposure at large
compressive strain. Compression creep experiments were performed at high temperature (150°C, 160°C, and
170°C) and under various conditions of steam pressure (Table 1). The compression processes were described
in detail by Kutnar and Kamke [1].
Load
[MPa]
5.5
Table 1: Test parameters and number of replicates for each compression treatment.
Temperature
Saturated
Compression loading steam
Venting time
[°C]
steam pressure
environment
prior to
[kPa]
compression [s]
150
469
Saturated steam
0
Transient conditions
10
160
614
Saturated steam
0
10
170
786
Saturated steam
0
Superheated steam
180
10
TOTAL
Number of
specimens
10
10
10
10
10
10
10
70
The applied compression treatment had significant effect on compressive deformation (Figure 1). The
instantaneous strain of 0.449 (approximately 7 seconds required to reach maximum load) was the smallest
under compression in superheated steam environment at 170°C. Comparison between the treatments at 170°C
showed that transient steam conditions caused larger instantaneous strain of 0.552, while the largest
instantaneous strain of 0.667 was achieved under saturated steam conditions. Furthermore, in transient steam
conditions the applied temperature affected the compressive deformation. Although unexpected, the largest
instantaneous deformation of 0.611 was achieved at 160°C and the smallest at 170°C (0.552), which was not
significantly different from 0.568 obtained at 150°C. In saturated steam conditions the applied temperature did
not have significant effect on instantaneous strain. The instantaneous strain of 0.667 was obtained at 170°C,
instantaneous strain of 0.690 at 160°C and instantaneous strain of 0.695 at 150°C. Past studies of stress-strain
curves in compression determined densification strain of 0.55 [2]. The compression in saturated steam at all
examined temperature caused instantaneous deformation that was well into the densification range of wood
material, while in transient conditions the instantaneous strain was at the limit of densification range.
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Cost-Action FP0904
Furthermore, in superheated steam conditions at 170°C the applied stress caused instantaneous deformation
that was in a cellular collapse range. Therefore, the observed creep behavior in saturated steam conditions was
dominated by the cell wall substance, with minor influence of cell wall buckling. While in superheated steam,
cell wall buckling dominated compression creep.
The creep deformation results were influenced by the degree of cell wall buckling at the time constant load
was achieved. If the cellular structure has already entered the densification phase (exceeded the yield strain and
most of the cells have collapsed) at the time of initiation of creep deformation, then the observed creep
deformation was dominated by the viscoelastic behavior of the cell wall substance. However, if the cellular
structure was still in the early plateau phase of compression, then more cell wall buckling could occur and
greater compression creep deformation was observed.
0.75
Compressive strain
0.7
0.65
0.6
0.55
0.5
0.45
0.4
0
25
50
75
100
125
150
175
Time [s]
170°C transient
170°C saturated
170°C superheated
160°C saturated
150°C transient
150°C saturated
160°C transient
Figure 1: Compressive creep strain of Douglas-fir specimens at 150°C, 160°C, and 170°C in saturated steam, superheated
steam, and transient conditions.
Acknowledgement: The project was supported by the National Research Initiative of the USDA Cooperative
State Research, Education and Extension Service, grant number 2006-35504-17444 and USDA Wood
Utilization Research Center Special Grant number 2008-34158-19302.
References
[1]
[2]
78
Kutnar, A., Kamke, A.F., 2010: Compression of wood under saturated steam, superheated steam and
transient conditions at 150°C, 160°C, and 170°C. Wood Science and Technology, published online
Oct. 8, 2010; DOI 10.1007/s00226-010-0380-0
Wolcott, M.P., 1989: Modeling viscoelastic cellular materials for the pressing of wood composites.
PhD Dissertation. Virginia Tech, Blacksburg, Virginia, 182 pp.
Cost-Workshop
Densification of Wood in Iran- State of the art
Ghonche Rassam1, Behnam Jamnani2
1
Depatment of Wood science and Technology, Faculty of Civil Engineering, Shahid Rajaee Teachr Training
University, Tehran, Iran P.O. Box 16785-163
[email protected]
2
Graduated Engineer of Natural Resources from Tehran University, Karaj, Iran
[email protected]
Key words: Densification of Wood, Hygrothermal Treatment, Hydrothermal Treatment, Nano-Silver, Iran
Abstract
Densification of wood because of its influences on improving mechanical properties, has been carried out since
1900. It has been conducted with or without some treatments such as thermal and hydrothermal treatments. In
Iran, also, some kinds of densification processes have been done. The main aim of this study is the introducing
some of these processes which can be described by 5 steps as below:
1)Hot steaming of wood before compression, densification through radial direction under different rates of
compression (Maximum 60%), just after steaming, and thermal treating after compression [1]. The main aim
of this process was the improving dimensional stability and mechanical properties. In fact, hot steaming
resulted in plasticizing of wood and hydrolyzing of hemicelluloses. Also, the presence of moisture during the
compression, increased thermal conduction from surface to the center of wood which decreased gradients of
density in thickness of wood. On the other hand, thermal treatment of wood decreased hydrophilic property of
wood, because of hemicelluloses degradation.
135
MOR (Mpa)
130
125
130.32
125.11
123.06 123.61
120
122.16
115.7
115
116.3
115.3
110
30%
60%
105
1h
3h
140ᵒᶜ 140ᵒᶜ
1h
3h
160ᵒᶜ 160ᵒᶜ
Figure 1: Bending strength of densified wood under different compression rates and thermal treatment conditions[1]
Although the degradation of hemicelluloses and parts of celluloses decreases mechanical properties but by
increasing the rate of compression, mechanical properties were improved (fig. 1).
2) Applying hydrothermal treatment before compression and densification through radial direction just after
treatment [2]. The main aim of this process was the improving dimensional stability and mechanical properties
by hydrolyzing of hemicelluloses and increasing of wood density.
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3) Densification of wood through radial direction without heat treatment, but under different conditions of hot
press such as different temperatures and rates of compression (maximum 50%) [3] and [4]. The Increase of
compression rate at lower press temperatures resulted in improving mechanical properties. But the increase of
both compression rates and press temperatures caused dimensional stability deterioration, because of high
pressure of vapor in wood and increase of mass per volume unit of wood that increased spring back and
swelling of wood, respectively.
4) Microscopic observation of wood cell wall deformation and stress-strain relationship under transverse
compression [5] and [6]. This method generated some basic understanding of micro-structural behavior of
wood under transverse compression. Early wood and late wood had varying degrees of influences on the
various segments of the grass stress-strain curve. In radial compression these features were seen: collapse in
early wood vessels, elastic deformation of late wood cells. In tangential compression, elastic deformation was
dominated by the bending of the late wood layers.
5) Nano-Silver impregnation of wood before radial compression and densification under different press
conditions such as different temperatures and durations of press [7]. In fact, silver with its high ability of
thermal conducting caused lower gradients in density profile. Also, high dimensional stability of these
compressed woods could be related to the bonding of Ag ions with hydroxyl groups in the cell wall.
It could be seen that applying some treatments such as impregnation of wood with nano-metal solutions,
thermal and hydrothermal treatments resulted in improving dimensional stability, comparing to those processes
which no treatment was applied. Also, by increasing the rates of compression in cases which plasticization by
steaming has been done before compression, mechanical properties have been improved significantly.
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
80
Rassam, G., (2010), Effect of thermal treatment on steamed densified wood, Report of Researching
Project, Shahid Rajaee Teacher Training University, Tehran, Iran.
Mohebby, B., Sharifnia-Dizboni, H., and Kazemi-Najafi, S., (2009), Combined Hydro-ThermoMechanical Modification (CHTM) as an Innovation in Mechanical Wood Modification, In the
Proceeding of: 4th European Conference on Wood Modification (ECWM4), Stockholm, Sweden,
353-360.
Safari, M., (1999), Study on the effects of hot press conditions on densified Carpinus betulus wood
properties, M.Sc Thesis, Tarbiat Modarres University, Noor, Iran.
Edalat, H., R., Tabarsa, T., and Reisi, M., (2008), Densification of Paullownia wood by using of hotpress, Iranian Journal of Wood and Paper Science Research 23(2) : 137-148.
Tabarsa, T., and Chui Y., H., (2000), Stress-strain response of wood under radial compression. Part I.
Test method and influences of cellular properties, Wood and Fiber science 32(2) : 144-152.
Tabarsa, T., and Chui Y., H., (2001), Characterizing microscopic behavior of wood under transverse
compression. Part II. Effect of species and loading direction, Wood and Fiber Science 33(2) : 223232.
Rassam, G., Taghiyari H., R., Jamnani, B., and Khaje, M., A., (2010), Effect of Nano-Silver
treatment on densified wood properties. Part one: swelling, recovery set, bending strength, Biarritz,
France: International Research Group of Wood Protection, Doc. No. : IRG/WP 10-40533
Cost-Workshop
Nanostructural and mechanical properties of
green, torrefied and welded softwood
Thomas Hecksher1, Kirsi Läppanen2, Jens Kai Holm3, Ritva Serimaa2,
Dorthe Posselt1
1
Roskilde University, Department of Science, Systems and Models, IMFUFA,
Universitetsvej 1, DK-4000 Roskilde, Denmark
2
University of Helsinki, Department of Physical Sciences, Division of X-ray Physics,
POB 64 (Gustaf Hällströmin katu 2), FIN-00014 University of Helsinki, Finland
3
Chemical engineering, DONG Energy, A.C. Meyers Vænge 9, DK-2450 Copenhagen
[email protected]
Key words: Nanostructure, softwood, mechanical recovery, torrefaction
Abstract
We have studied the nanostructural changes of softwood when subjected to external stress such as heat,
mechanical strain, pressure or dehydration. Here, we have focused especially on the relation between
nanostructure and the mechanical properties in three cases: the molecular mechanism behind mechanical
recovery after plastic deformation [1], the nanostructural changes causing brittleness after torrefaction (mild
pyrolysis) [2], and the nanostructural changes in the bond zone of wood welded samples [3].
The recovery mechanism [1] is suggested to be universal and is described as a velcro-like stick-slip mechanism
related to the entanglement of hemicellulose polymers between the cellulose microfibrils inside the softwood
cell wall. Modelling the polymer interactions, however, point to an alternative model in which hemicellulose
chains bridging continuously from one microfibril aggregate to the next provide most of the necessary
cohesion [4] while the stick-slip mechanism is explained by breaking and reforming bridging bonds along the
microfibrils. More experimental data are thus called for to provide a basis for the discussion on which model is
more likely to explain the mechanical recovery and dynamical behaviour generally.
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Figure 1: Top left: The conceptual setup of the experiment. All the samples were cut in sheet geometry (dimensions radial x
tangential x longitudinal = 0.2-0.4mm x 2-3mm x 30mm) using a sliding microtome. The samples were subject to alternating
straining at constant strain rate and being kept fixed for 30-600 seconds at constant strain. The straining continued until
rupture. The green samples were kept moist during the experiment using a medical infusion system. We used strain rates of
0.01mm/min – 10mm/min and temperatures were in the range ambient to 90C. Top right: typical tensile stress-strain data
from a compression softwood sample - here with three stress relaxations at ambient temperature. Bottom left: The azimuthal
intensity profile from 2D SAXS data (integration limits from 0.08 Å−1 to 0.23 Å−1 in a 1◦ sectorial window) and a simple
MFA distribution model in reciprocal space based on the sum of three Gaussian functions fitted to the data [5]. The inset
shows a SAXS pattern from moist softwood. The cellulose microfibril angle determined from SAXS for this sample is 21o.
Bottom right: The normalized mean MFA as a function of temperature. The data was collected every 2 minutes and
analyzed with a 30 minutes running window.
We have studied the structural changes of moist green compression wood as a function of strain rate and
temperature and dry, torrefied softwood using time resolved (down to 5s per frame) Small-Angle X-ray
Scattering (SAXS) in combination with tensile tests. SAXS on wood gives information on the cellulose
microfibril angle (MFA) and the short range order of the cellulose microfibrils in the cell wall. The tensile
measurements give information about the modulus of elasticity, and the stress relaxation. Data has been
obtained using a laboratory setup (sealed x-ray tube and a Tinius Olsen tensile stage) and at a large scale
facility (synchrotron radiation at BW4, HASYLAB and a beamline tensile stage) which allowed for the
structural changes to be studied in situ during the recovery stress relaxation in the plastic range.
The studies show that the recovery stress relaxation depends strongly on the strain rate but very little on the
temperature. Conversely, the modulus of elasticity depends on the temperature but not on the strain rate.
Further studies on the dynamical nature of the recovery mechanism should therefore take the strain rate into
account. The recovery stress relaxation and the features of the stress-strain curves are qualitatively the same for
both never-dried compression wood as well as the rehydrated early and late wood. This supports the proposed
universality of the mechanism. The initial mean MFA is lower than found in [1] (between 14◦-29◦ opposed to
25◦-50◦) and decreased linearly throughout the straining experiment independently of temperature.
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A detailed understanding of the structural and mechanical properties of green softwood provides the basis for a
discussion of changes occurring in torrefied and wood welded samples. A spatial SAXS scan over the bonding
zone of a wood welded sample shows a gradual transition from order to disorder with respect to the orientation
of the cellulose microfibrils. Data from static SAXS measurements on torrefied wood samples as function of
torrefaction temperature will be presented. The torrefied samples are very brittle thus the samples in many
cases broke before tensile data could be obtained, however a few cases will be discussed.
Acknowledgements: We would like to thank: Torben Steen Rasmussen, Ebbe Hyldahl Larsen and Preben
Olsen at the workshop at IMFUFA, Roskilde University for the construction of the heating device. Pekka
Saranpää and Tapio Järvinen at the Finnish forest research institute METLA for providing green compression
wood samples (Pinus sylvestris, Scots pine) help cutting the samples. The biosystems division at Risø for use
of facilities to make torrefied samples.
References
[1]
[2]
[3]
[4]
[5]
J. Keckes, I. Burgert, K. Frühmann, M. Müller, K. Kölln, M. Hamilton, M. Burghammer, S. V. Roth,
S. Stanzl-Tschegg and P. Fratzl, Nature Materials 2 (2003) 810.
P. Bergman and J. Kiel, ECN-RX–05-180, 14th European Biomass Conference & Exhibition (2005)
B. Gfeller, M. Zanetti M. Properzi, A. Pizzi, F. Pichelin,M. Lehmann and L. Delmotte, J. Adhesion
Sci. Technol., 17 (2003)1573
C.M. Altaner and M.C. Jarvis, J. of Theoretical Biology 253 (2008) 434
A. Reiterer, H.F. Jakob, S.E. Stanzl-Tschegg and P. Fratzl,Wood Science and Technology 32 (1998)
335-345
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84
Cost-Workshop
Measurement of the Density Distribution in Wood Using X-Ray Tomography
J. Schreiber1, P. Haller1, and U. Hampel2
1
2
Institute of Steel and Timber Structures, TU Dresden, Germany
Eisenstuckstrasse 33 HH, 01062 Dresden
[email protected]
[email protected]
Forschungszentrum Rossendorf, Institute for Safety Research, Experimental Thermofluiddynamics
Postfach 51 01 19, 01314 Dresden
[email protected]
Key words: wood density measurement, computed tomography, X-ray imaging
Abstract
Soft wood has a porosity of about 60% and allows slight plastic deformation perpendicular to the grain at
temperatures of 140°C and pressure of 5 MPa. Thus, the cross section can be approximately halved whereby
the microstructure of the wood folds up because the lignin has been softened. Due to this thermo-mechanical
treatment strength and stiffness can be increased proportionally to densification. Furthermore, it is possible to
reverse and fix the compression without causing any damage to the microstructure (Haller 2004). Soft and hard
wood are both suited for this.
At the Institute of Steel and Timber Structures, TU Dresden glued laminated timber boards were made and
densified in the direction of the plane. Afterwards prismatic cross sections were produced by reversing the
compression. The results of the foremost investigations were stress-strain-diagrams by consideration
temperature and moisture. So far only a few investigations on the density as major firmness factor have been
reported. To analyze the density and their distribution during the process steps (consolidating and back
forming) the method of X-ray tomography may be used. The main advantage of CT imaging over conventional
techniques for wood bulk density determination is that it allows detection and quantification of density
distribution, heterogeneities and internal defects. Malan, Marais (1992) have shown that air dry wood density
determination from CT images gives high accuracy compared to the gravimetric method. This was expected as
most wood species have a similar chemical composition (30-50 % cellulose, 15-35 % hemicellulose and 15-30
% lignin) (Lindgren 1992).
Therefore, we may determine the density and their distribution by CT imaging in the form of density profiles.
Due to the similarity in chemical composition the density can be directly inferred from the reconstructed grey
values. The first specimens we examined were tree discs (diameter 90mm) and cuboids (120mm x 120mm x
40mm). For comparing the density values they were measured before and after compression. To calculate the
density profiles of the non-densified and densified wood a grey value based algorithm was used. Therefore we
consider wood as a compound material, consisting of sheer wood substance (1500kg/m³) and locally varying
ϕ . Knowing the grey values corresponding to sheer air and to sheer wood substance
ϕ from the local grey value. Once knowing ϕ the local wood density of
one can calculate the local value of
amount of air denoted
this point can easily be calculated (Vogel et al. 2002).
For CT imaging we used a medical X-ray tube (Comet DI-104H-2260-150) and a flat array detector (PerkinElmer RID 1640) with a spatial resolution of 0.4mm. Detector and source are stationary and the sample was
placed closely in front of the detector. The measurements were accomplished at a tube voltage of 90kV and a
tube current of 1mA.
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The test results showed that both kind of timber are well suited for compression. The main reason is their high
pore volume. The density profiles achieved by tomography showed that both species were in tangential
direction homogeneous compressed. In radial direction earlywood compressed significantly better than
latewood and most compression was inserted in earlywood. Comparing the absolute density values, spruce
showed greater differences between early and latewood. The reason for that are the inhomogeneous tree rings
of spruce. Overall in the radial direction poplar was slightly better compressed because of the homogeneous
tree rings. In both, spruce and poplar, 15% of the density remained within even after recovery in water.
These results from densifying and recovering as the physical phaenomens of forming the tubes are used to
verify material constitutive laws. For example a simulation is based on a ratio of stiffness from 1:6 between
early and latewood. In comparing the figures from test result and simulation the deformed mesoscopical
structure seems to be similar.
Figure 1: Mesoscopical structure seems to be similar (fig. l. and m.); CT visualizes inner microstr. deformations (fig.r.)
Only the CT figure visualizes inner micro structural deformations so that the numerical simulations can be
improved for deriving a material constitutive law.
Acknowledgement: The project was funded by Deutsche Bundesstiftung Umwelt (DBU). The CT
measurements are made at the Institute of Safety Research of Forschungszentrum Dresden Rossendorf (FZD).
The responsibility for the content of this publication lies by the authors.
References
[1]
[2]
[3]
86
Haller, P.: Vom Baum zum Bau oder die Quadratur des Kreises. Wissenschaftliche Zeitschrift der
Technischen Universität Dresden, 53 (2004), Heft 1-2.
Malan, F.S., Marais, P.G.: Some Notes on the Direct Gamma Ray Densitometry of Wood.
Holzforschung, 46 (1992), 91-97
Lindgren, O. Non-destructive wood density distribution measurements using computed tomography.
Holz als Roh- und Werkstoff, 50 (1992), 295-299
Cost-Workshop
Instantaneous Wood Distortion under High Temperature Drying
H. Pearson1, B.L. Gabbitas2, S. Ormarsson3
1Scion, Rotorua, New Zealand
[email protected]
2School of Engineering, University of Waikato, New Zealand
[email protected]
3Department of Civil Engineering, Technical University of Denmark, Denmark
[email protected]
Key words: Wood distortion, high temperature drying, internal stress, radiata pine, kiln drying
Abstract
Internal stresses develop in wood during moisture conditioning because of its hygroscopic properties and
unequal shrinkage behaviour in the three grain directions. However, such stresses can be inherently difficult to
detect. External wood distortion usually indicates the presence of internal stress but all stress may have been
relieved through such distortion. Conversely, wood, which shows no external distortion, may still exhibit an
internal stress imbalance which can lead to distortion after sawing. Stress effects associated with kiln drying
can result in significant sawn lumber product degrade as a result of warping and checking.
Two methods exist to assess internal stress in wood as a result of moisture change. The first method is direct
measurement, as with prong and slices tests, and the second method is to model internal stress. Direct
measurement assessments are usually unable to be performed during moisture conditioning and are invasive in
that they lead to sample destruction. Conversely stress modeling is predictive and requires fundamental wood
material properties and complex software to solve the mechanical equations in space and time.
A work programme was initiated at Scion, New Zealand, with the overall goal of collecting high temperature
(70 to 150ºC) material properties for use in modeling the stress developed in radiata pine during high
temperature kiln drying. A key focus was also to design and develop equipment to accurately measure
fundamental material properties required for such modeling. The study was designed to extend an earlier three
dimensional distortion model developed by Ormarsson (2000) to predict drying stress in wood up to a
temperature of 70°C where the total strain equation was assumed to consist of the summation of elastic,
moisture-induced shrinkage, mechanosorptive and creep deformations. Each component of the total strain
equation was studied separately with respect to the variables stress, time, temperature and moisture content
using purpose designed equipment and the results combined in a finite element stress model.
Experimental material property results for tangential grain, tensile, radiata pine (Pinus radiata D.Don)
sapwood samples were combined into an instantaneous distortion model to predict stress or distortion as a
function of temperature, moisture content and either external load or distortion. All samples were taken from
one representative plantation tree from which wood quality information was obtained for a covariate analysis
of the results. This included basic wood density, spiral grain, conic angle, and cardinal point mean microfibril
angle which was obtained using SilviScan. Poissons' ratios were estimated from digital speckle photography
experiments perfomed using an Aramis system at 20°C whilst the remaining compliance matrix variables such
as shear moduli and moduli of elasticity for longitudinal and radial grain directions were estimated from
published ratios.
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The distortion model architecture involved Python code for use as an input into Abaqus software with Fortran
subroutines. For each study a moisture field output file, based upon the chosen constant temperature, was
obtained for each geometric sample element and the results used as an input into the stress model. Stress model
results were compared with representative experimental results from instantaneous, free shrinkage and
mechanosorption studies.
Results showed good agreement between the model and instantaneous elastic, free shrinkage and
mechanosorption experimental results for tensile sample geometries, provided a 'thermo-sorptive-aging' effect
was used to compensate for reduced hygroscopicity, if wood was alternately wet and re-wet in a cyclic fashion.
A full board distortion model was then used to test the resultant stresses associated with wood that was dried to
5% moisture content followed by steaming to simulate final stress relief as implemented by industry. As
expected, full board model results revealed the average stress in the longitudinal, radial and tangential
directions to decrease after steaming, compared to drying with no steaming. Even though internal stresses from
modelling were higher after steaming compared to only drying, total stress was improved. This theoretically
caused less external distortion in a simple geometry like a board, although creep was not included in the
simulations and may help to equalise internal stress further over time. Stress result profiles within the board
agreed with earlier studies for two dimensional distortion by Chen et al (1997b).
The three dimensional high temperature distortion model that was developed as part of this work is a valuable
tool for distortion assessment compared to one- or two-dimensional models that are limited to a single plane.
Future work will seek to optimise moisture conditioning schedules and thermo-hygro-mechanical treatments
using the full board distortion model with full mechano-sorptive-creep analysis.
Acknowledgement: Scion, Rotorua, New Zealand for the provision of experimental facilities and the New
Zealand Government for funding this research.
References
[1]
Ormarsson, S., Dahlbom, O., Petersson, H., A numerical study of the shape stability of sawn timber
subjected to moisture variation. Part 3: Influence of annual ring orientation, Wood Science and
Technology, 2000, Vol 34, 207-219.
[2]
Chen, G., Keey, R. B., Walker, J. C. F., The drying stress and check development on hightemperature kiln seasoning of sapwood pinus radiata boards. Part II: Stress development, Holz als
Roh-und Werkstoff, 1997b, Vol. 55, 169-173.
88
Cost-Workshop
Numerical Simulation of Wooden Structures under Mechanical and Moisture
Loading
Michael Kaliske1, Susanne Saft2
Institute for Structural Analysis
Technische Universität Dresden,
D-01062 Dresden, Germany
1
[email protected]
2
[email protected]
Key words: material modeling, plasticity, ductile failure, brittle failure, cohesive elements, moisture diffusion,
hygro-mechanical coupling, moisture-induced stresses
Abstract
Besides mechanical loads, wooden constructions are exposed to changes of the ambient atmosphere, such as
relative humidity (RH) and temperature. The natural biopolymer wood responds to this by means of changes of
moisture content and wood temperature. Both of these quantities obviously influence the mechanical behavior
of wooden structures, since phenomena like swelling, shrinkage and thermal expansion exist. Within the limits
of natural room temperature, the influence of moisture content strongly prevails. Since this temperature range
is sufficient for the particular object of our current research, the presented model focuses on the coupling of
mechanical behavior and moisture transport. Thereby, moisture diffusion, hygro-expansion and moisturedependent linear elastic behavior, ductile and brittle failure is covered. Since the model is aimed to be
applicable to wooden engineering structures, continuum macro-mechanical approaches are used, which can be
applied within the framework of the FEM. Long-term effects are not considered.
All material properties that describe the mechanical behavior of wooden structures are more or less dependent
on moisture content, thus, this influence has to be considered for a realistic simulation. Since we focus on the
modeling of ductile and brittle failure, the influence of moisture content on the stiffness and strength properties
as well as fracture energies is of interest. When moisture content increases, the quantities of stiffness and
strength properties initially slightly increase and then decrease with different magnitude until the fiber
saturation area (FSA) is reached. Though, the influence of moisture content on strength properties is much
more distinctive then on stiffness properties. In contrast, the values of fracture energy increase with increasing
moisture content – the material becomes less brittle (see Figure 1). In many studies, experimental
investigations on the moisture dependency of particular mechanical properties are published. Often, the
measured data is additionally approximated by regression functions. Nevertheless, a significant lack of
knowledge is found in this field, since no publication is providing a complete set of moisture dependent
mechanical properties, not even for one wood species. A complete set of moisture dependent stiffness
properties of spruce wood has been published by Neuhaus [6] by means of a moisture dependent compliance
matrix. In many publications, the moisture dependency of mechanical properties is simplified as being linear.
Besides the moisture dependency of the mechanical properties, moisture-induced volume changes have to be
considered for the realistic simulation of the short-term hygro-mechanical behavior of wood. Due to the
absorption of moisture into the micro-capillaries, the cell walls expand until FSA is reached. This leads to
swelling of the wood structure. When FSA is exceeded, no more swelling is observed. The amount of lengthchange (or strain) due to swelling and shrinkage significantly depends on the material direction and the wood
species.
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Compared to other construction materials like for example steel, concrete or rubber, the number of publications
on material models for the simulation of wood is small. Especially hygro-mechanically coupled models for the
simulation of the short-term behavior are rare. The goal of this work is the introduction of a macroscopic threedimensional constitutive model for the simulation of ductile and brittle failure of mechanically and moisture
loaded wooden structures. The model for the simulation of hygro-mechanically coupled ductile failure bases
on the multi-surface plasticity model with C1-continuous yield surface introduced in [2]. To ensure the
convergence of the incremental iterative solution procedure, the particular terms of the compliance matrix have
to be derived. For the modeling of brittle failure, cohesive elements with an appropriate material model are
used, basing on the formulation of [3]. Moisture diffusion in wood below FSA is modelled with the help of
Fick’s Law.
Figure 1: Simulation of moisture-dependent brittle failure
Numerical modeling coupled hygro-mechanical behavior offers the possibility to more realistically simulate
the characteristics of wood and with that to understand better the processes within a wooden structure since
experimental investigations do not allow to look inside.
References
[1]
[2]
[3]
90
Neuhaus, H., (1983), Über das elastische Verhalten von Fichtenholz in Abhängigkeit von der
Holzfeuchtigkeit [About the elastic behavior of spruce wood dependent on its moisture content],
Holz als Roh- und Werkstoff 41: 21-25.
Resch, E., Kaliske, M., (2010), Three-dimensional numerical analyses of load-bearing behavior and
failure of multiple double-shear dowel-type connections in timber engineering, Computers and
Structures 88: 165-177.
Schmidt, J., Kaliske, M., (2007), Simulation of cracks in wood using a coupled material model for
interface elements, Holzforschung 61: 382-389.
Cost-Workshop
The thermo-hydro-mechanical behavior of wood during composite
manufacture
Heiko Thoemen
Bern University of Applied Sciences, Architecture, Wood and Civil Engineering
Solothurnstrasse 102, P.O. Box, CH-2500 Biel-Bienne 6
[email protected]
Key words: Heat and mass transfer, rheology, wood-based panels
Abstract
Introduction
The thermo-hydro-mechanical characteristics of wood play a crucial role during manufacture of wood-based
composites such as particleboard, medium density fiberboard (MDF) and oriented strandboard (OSB). When
drying the wood particles or fibers, high temperatures up to several hundred centigrade are applied. Besides
driving out the water from the wooden elements the severe conditions during drying may also change the
chemical structure of the wood itself, leading to an alteration of its sorption behavior. During hot-pressing of
the wood-furnish mat, again high temperatures (up to 220 C) act upon the wood. When heating the mat
surfaces, a rather complex interaction between heat transfer, moisture changes, plasticization and densification
of the particles or fibers, and adhesive cure is triggered. And finally, the raw panels may, again, face high
temperatures during coating or other further treatment procedures such as thermo planing of its edges.
A sound understanding of the thermo-hydro-mechanical behavior of wood and the complex interactions
associated to this behavior is needed if we want to use the wood in an efficient manner, and if we want to
optimize composite products and the relevant processes. In this extended abstract the focus is put on the hotpressing of the wood furnish mat as an example. An approach to model the relevant physical mechanisms is
given.
Hot-pressing of wood-based composites
In the press, high temperatures and compaction pressures are applied to consolidate the loosely formed mat of
adhesive-treated wood particles. Heat is transferred from the heating platens to the mat surfaces, and from
there towards the central plane of the mat. The heat is required to plasticize the wood particles and to cure the
adhesive bonds. As a consequence of heating, moisture also migrates in the form of vapor towards the central
plane and escapes through the edges of the mat. A simplified drawing of the relevant heat and mass transfer
mechanisms is given in Figure 1a. Both mechanisms, heat transfer by conduction and convection are essential
during hot pressing. As can be shown by simulation results (Figure 1 b) there is a convective heating front
moving from the surfaces towards the central plane of the mat, while conduction is the dominant heating
mechanism between the heating platens and this convective front, but also inside the mat during the first phase
of hot-pressing. [1]
The rheological properties of the material depend interactively on temperature and moisture content. Hence,
the non-uniform temperature and moisture distribution that prevails during the pressing cycle in combination
with the course of pressure applied from the press to the mat causes a differential densification of the mat,
establishing a cross-sectional density profile (Figure 2). The density profile dramatically influences not only
the mechanical properties of the product, but also its thermal and diffusive characteristics and its behavior
during further processing. Understanding the combined effects of heat and mass transfer and of the rheological
characteristics of the wood-furnish mat is the prerequisite to be able to efficiently manipulate the density
profile formation during panel manufacture. [2]
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White area:
condensation
of water vapor
gas and heat
convection
evaporation
of water
Specific rate of
Heating, Q*
[kJ/(kg·s)]
heat
conduction
*
*
Qconv
> Qcond
6
4
2
0
> 200°C
0
200
400
0
25
50
75
100
600
(a)
(b)
Figure 1: (a) Basic heat and mass transfer mechanisms inside a wood furnish mat during hot-pressing. (b) Simulated specific
rate of heating during hot-pressing of an MDF mat. The white area displays those regions where convective heating
dominates over conductive heating.
Panels are typically manufactured with an adhesive content of 3 to 10 % (on a dry mass basis). The curing
reaction strongly depends on the course of the temperature development, but also on the localized and
changing moisture conditions inside the mat during pressing. The bond strength developing between the
individual wood particles has a strong influence on the integrity of the final panel, but also affects the
rheological behavior of the wood-furnish mat. Consequently, the development of the cross-sectional density
profile and the build-up of internal stresses are influenced by the course of the adhesive cure. Above, the
adhesives may also interact with other mechanisms during hot-pressing. For example, (P)MDI is one of the
adhesives used in panel manufacture. This adhesive type is known to soften wood when penetrating it. Hence,
the mechanical behavior of the wood particles during compression is believed to be influenced not only by
temperature and moisture, but also by the adhesive if (P)MDI is used.
150
100
1000
50
750
0
0
0
500
10
20
40
250
0
20
60
80
0
10
30
20
0
20
40
60
30
80
(a)
(b)
Figure 2: Development of the cross-sectional temperature (a) and density (b) profiles during hot-pressing of an MDF mat in
a continuous press.
References
[1]
[2]
92
Carvalho, L., J. Martins, and C. Costa (2010): Transport Phenomena. In: H. Thoemen, M. Irle, and
M. Sernek (Eds.). Wood-Based Panels - An Introduction for Specialists. Published by Brunel
University Press, London: 123 - 176.
Thoemen, H., C. Haselein, R., and P. E. Humphrey (2006): Modeling the physical processes relevant
during hot pressing of wood-based composites. Part II. Rheology. Holz Roh- Werkst. 64(2): 125133.
Cost-Workshop
Densification of Wood Veneers with Heat and Steam Combined with Oil-Heat
Treatment
Chang-Hua Fang1, Alain Cloutier1, Pierre Blanchet1,2, Ahmed Koubaa3
1
Centre de Recherche sur le Bois (CRB), Département des Sciences du Bois et de la Forêt,
Université Laval, Québec, QC, Canada
2
Value-Added Products Department, FPInnovations, Québec, QC, Canada
[email protected]
3
Unité d'Enseignement et de Recherche en Sciences Appliquées, Université du Québec en AbitibiTémiscamingue (UQAT), Rouyn-Noranda, QC, Canada
[email protected]
Key words: wood densification, heat treatment, compression, veneer, aspen, dimensional stability, oil
Abstract
Wood densification by compression is known to improve wood mechanical strength but dimensional stability
is often a problem due to compression recovery [1-5]. Oil-heat treatment (OHT) is known to improve wood
dimensional stability and enhance its resistance to biological attack. In this study, wood densification and OHT
were combined to improve wood mechanical properties and dimensional stability. Large aspen (Populus
tremuloides) wood veneer specimens of 700 × 700 mm were densified in a 862 × 862 mm steam injection hot
press under the effect of heat, steam, and pressure at temperatures of 160ºC, 180ºC, and 200°C, respectively.
Holes used for steam injection and venting are distributed on both platens at 32 mm intervals. The two platens
were pre-heated before treatment. Veneers were pre-treated with steam at a line pressure of 550 kPa, and then
compressed from initial to target thickness at a maximum hydraulic pressure of 4.5 to 9.0 MPa. After
densification, platens were maintained in the same position. At the end of treatment, steam injection was
stopped and steam was vented through the holes in the platens. Platens were opened and the veneer was
removed from the press. Theoretical compression set was 50%. After densification, average oven-dry thickness
and standard deviation were 1.61± 0.09 mm. Samples of 50 × 50 mm (tangential × longitudinal) were cut from
the densified veneers with a laser cutter. They were treated in a hot canola oil vessel at 180ºC, 200ºC, and
220ºC for 1, 2 and 3h. A cyclic recovery test was conducted to determine compression set recovery. Figure 1
shows the results obtained. Tests were also performed on some physical and mechanical properties, such as
density, hygroscopicity, swelling, irreversible swelling (IS), anti-swelling efficiency (ASE), Brinell hardness,
and tensile and bending strength.
Average oven-dry density and standard deviation before and after densification were 388 ± 25 kg/m3 and 830 ±
64 kg/m3, respectively. Veneers darkened after densification and darkening increased in intensity with
increased densification temperature. After densification, lathe checks that were present on veneers before
densification were conglutinated and veneer surface roughness decreased.
For the densified veneers without OHT, it was found that densified veneers showed markedly reduced
hygroscopicity, and the higher the densification temperature, the lower the hygroscopicity. The Brinell
hardness of densified veneers was about two or three times that of control for both aspen and hybrid poplar.
Tensile and bending strength also improved significantly after densification. However, these mechanical
properties of densified veneers decreased to some extent with increased densification temperature. The
modulus of elasticity in tension and bending increased after densification, especially at high temperatures.
Very high compression set recovery was found for veneers densified at low temperatures. Recovery decreased
dramatically when densification temperature exceeded 180°C.
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OHT was shown to be efficient for improving the dimensional stability of thermo-hygromechanically densified
veneers. After OHT, a marked reduction in compression set recovery was found in densified veneers. Both
OHT temperature and duration had a marked influence on the reduction of compression set recovery. The
higher the OHT temperature and duration, the lower the recovery. Recovery was reduced to less than 5% under
various OHT conditions. Recovery values of about 0% were achieved under some OHT conditions: OHT at
180°C for 3h for specimens densified at 200°C; OHT at 200°C for 3h; and OHT at 220°C (Fig.1). Both radial
and tangential swelling in densified veneers were reduced dramatically. Compared to OHT duration, OHT
temperature had a more pronounced impact on radial and tangential swelling. Irreversible shrinkage in the
compression direction in densified veneers decreased after OHT, particularly with high-temperature and longduration OHT. Anti-swelling efficiency in the compression direction improved significantly after OHT, and
OHT temperature showed a pronounced positive effect on ASE. Mechanical properties decreased to some
extent after OHT. OHT temperature, compared to duration, had a more pronounced impact on mechanical
properties.
Control
Control
Figure 1: Compression set recovery for veneers densified at 160°C (diamonds), 180°C (circles), and 200°C (squares),
respectively, with OHT at 180°C, 200°C, and 220°C for 1h, 2h, and 3h, respectively, and for Controls (without OHT). D
stands for oven-dry.
References
[1]
[2]
[3]
[4]
[5]
94
Navi, P., and Heger, F. (2004). "Combined densification and thermo-hydro-mechanical processing of
wood," Materials Research Society Bulletin 29(5), 332-336.
Navi, P., and Girardet, F. (2000). "Effects of thermo-hydro-mechanical treatment on the structure
and properties of wood," Holzforschung 54(3), 287-293.
Inoue, M., Norimoto, M., Tanahashi, M., and Rowell, R. M. (1993a). "Steam or heat fixation of
compressed wood," Wood Fiber. Sci. 25(3), 224-235.
Ito Y, Tanahashi M, Shigematsu M, Shinoda Y (1998a) Compressive-molding of wood by highpressure steam-treatment: Part 2. Mechanism of permanent fixation. Holzforschung 52(2): 217-21.
Kamke FA (2006) Densified radiate pine for structural composites. Maderas. Ciencia y tecnología
8(2): 83-92.
Cost-Workshop
The mechanical behaviour of formed wood profiles
Dr.-Ing. A. Heiduschke 1, Prof. Dr.-Ing. Peer Haller 2
1
Institute of Steel and Timber Structures, Technische Universität Dresden,
01062 Dresden, Germany
[email protected]
2
Institute of Steel and Timber Structures, Technische Universität Dresden,
01062 Dresden, Germany
[email protected]
Key words: formed wood, timber profiles, FRP
Abstract
The objective of this research is to provide engineered wood products on the basis of formed wood profiles for
structural applications. The formed profiles can be optionally reinforced with technical fibers and/or textiles
laminated to the outer wood surface. The purpose of such composite confinement is to strengthen the relatively
thin-walled sections and to protect the wood against environmentally induced damage. This paper discusses the
load-carrying behavior of light-weight columns with circular hollow cross section. Full-scale axial
compression tests were conducted to evaluate the structural performance of the tubes. Following parameters
were investigated: (a) type of fiber reinforcement, (b) fiber orientation, (c) thickness of the reinforcement, (d)
loading conditions - centric or eccentric, (e) slenderness of the tubes and (f) influence of connections. The
static tests have shown that wooden tubes are capable of sustaining high buckling loads as far as brittle failure
modes can be prevented. Such failure type was observed for unreinforced columns. The longitudinal splitting
of the profiles was due to the expansion of the tubes in circumferential direction resulting in a tension
perpendicular to grain failure. The tests on reinforced tubes demonstrated that load-carrying capacity and
ductility of timber profiles can be significantly enhanced by composite confinement. The failure mode that
caused the damage of the reinforced columns was compression failure in wood. The experimental results
reveal that the relatively thin-walled sections (fiber reinforced) are not prone to local buckling failure due to
geometrical discontinuities or imperfections. The innovative developments may set the basis for the future of
high capacity timber structures, especially in case of highly loaded members with large cross sections.
In timber construction, round or rectangular solid cross sections prevail. Compared to technical profiles, the
area of these cross sections only yields a poor moment of inertia.
The presented research work deals with the testing and analysis of wooden tubes reinforced with FRP
composites. Because of the good compatibility of wood and FRP, both materials can benefit from synergies.
On one hand, wood profits from the outstanding mechanical and physical characteristics of FRP with load
adapted fiber confinement strengthening the wood in transversal direction. On the other hand, FRP can profit
from the mechanical characteristics, environmental friendliness and low price of the wood. Fiber or textile
reinforced wooden profiles can be created by employing different techniques – by means of braiding and
winding techniques or by wrapping the profile with woven or non-woven fabrics (pull over tubular knitted
fabrics) – see Figure 1.
Proposed circular hollow sections are well suited for columns because they behave well when subjected to
axial forces, bending moments and torsion. Compared to sawed and glued laminated timber, formed wood
profiles have some characteristics that require testing. To evaluate the performance of FRP confined wooden
profiles, full-scale axial compression tests were conducted. The test set-up of a 3.8 m column is shown in
Figure 2.
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Figure 3 shows the load-displacement curves for selected columns with a length of 2.5 m. In average the
reference tubes reached an ultimate load of 564 kN corresponding to compression stress of 41.6 N/mm2. The
load-deformation behavior until failure is linear elastic. Compared to the reference specimen, remarkably
higher loads and ductility levels were obtained with the FRP reinforced tubes. The average ultimate load for all
types is 900 kN corresponding to compression stress of 56.7 N/mm2. With reference to the unreinforced tubes,
this is an increase of about 60%. The experimental data reveal that the columns with a 45° confinement
(FRP45) had higher ductility than the FRP85 columns.
Figure 1: a) braiding and (b) winding of wooden
tubes, (c) tube with a tubular knitted fabric
Figure 2: Test set-up of
a carbon reinforced
column
Figure 3: Load-displacement curves of REF
and FRP reinforced tubes
From the experimental results it can be concluded that:
•
GRP and CRP reinforced tubes behave similarly. The influence of the type of fiber (glass or carbon)
is negligible, as far as the fibers are primary oriented in circumferential direction (±45° to ±90°) and
act as a classical confinement. In this case the strength of the composite is the decisive parameter,
which is similar for glass and carbon composites.
•
In order to take advantage of the high stiffness of the carbon composite, the fibers need to be
oriented in the direction of the applied load (into the column axis ~ 0°).
•
The tests showed that a relatively small degree of reinforcement (less than 1 mm in circumferential
direction) is sufficient to avoid splitting of the tubes. A further increase in confinement thickness is
inefficient. Only additional carbon fibers, oriented in column axis will significantly improve the
structural performance.
•
The eccentric loading (60 mm off axis) resulted in a decrease in load-carrying capacity of about 25%
(min 12%, max 43%).
•
Since the differences in load-carrying capacity between FRP tubes having a length of 0.8 m and
2.5 m are small, it can be concluded that the testing of short cylinders is sufficient for determining
the ultimate load of compact columns (of intermediate length) with no risk of buckling (Euler type).
•
In general, connections have a large influence on the load-carrying capacity of structures. Glued
connections can reach the strength of non-connected, clear sections. In case of large finger joints, it
can be assumed as conservative that the strength of the connection reaches at least 80% of the
strength of a clear section.
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Cost-Workshop
Wood surface densification by compression: Analysing the effect of process
parameters
Kristiina Laine1, Lauri Rautkari2, Mark Hughes3, Nick Laflin4
1
Aalto University
P.O. Box 16400, FI-00076 Aalto, Finland
[email protected]
2
Aalto University
[email protected]
3
Aalto University
[email protected]
4
Bangor University,
Deiniol Road, Bangor, Gwynedd, LL57 2UW, United Kingdom
[email protected]
Key words: surface densifying, Scots pine, wood compression, density profile
Abstract
Density is one of the most significant factors affecting the mechanical properties of wood. Scots pine has a
relatively low density and increasing its density would widen the range of applications for this species. In this
study Scots pine sapwood samples were densified by compressing the porous structure under heat and
moisture. Densifying one side of wood aims at applications that require only one harder surface, such as
flooring. Surface densification has been studied mainly in Finland, the United States, Canada, and Japan. [1-5]
This study evaluated the significance of different process parameters (temperature, closing time, holding time,
moisture content, and compression ratio) on wood surface densification and their effect on the wood density
profile. Furthermore, microscopic analysis was performed on a selection of samples.
The results of this study indicate that a shorter closing time of 0.5 minutes resulted in the deformation being
significantly higher and closer to the densified sample surface than with a longer closing time of 5 minutes.
Using a compression temperature of 150 ºC the density curve also exhibited a higher peak closer to the sample
surface, while a higher temperature of 200 ºC resulted in the highest density peak being lower and further from
the surface. A longer holding time of 10 minutes exhibited a density increase over a wider section of the
sample thickness than when using a shorter holding time of 1 minute. However, the highest peak was slightly
closer to the sample surface with the shorter closing time. Higher moisture content led to deeper deformation.
However, the highest moisture content of 15.6 % (conditioned at RH 75 %) exhibited a lower densification
ratio than moisture contents of 12.4 % (RH 65 %) or 9.6 % (RH 35 %).
The manner of wood deformation in compression can be controlled by optimizing the process parameters and
thus achieving desired properties. This method of densifying wood has not been widely investigated but it
already shows great potential and requires further investigation for commercial production.
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1100
1000
900
2
Density [kg/m ]
800
700
600
500
400
300
200
100
0
0
2
4
6
8
10
12
14
16
Position [mm]
Figure 1: Scots pine sample (conditioned at RH75%) compressed at 150°C with closing time 0.5 min and holding time 10
min and compression ratio 25 %.
Figure 1 exhibits a density profile of a Scots pine sample compressed at 150 °C with closing time 0.5 min and
holding time 10 min. Original thickness of the sample was 20 mm and it was compressed to 15 mm
(compression ratio 25 %). The sample was compressed against a heated plate, which was on the right side of
the sample in the figure.
References
[1]
[2]
[3]
[4]
[5]
98
Inoue., M., Norimoto., M., Otsuka., Y. and Yamada., T., (1990), Surface compression of coniferous
wood lumber I, Mokuzai Gakkaishi 36(11) : 969-975.
Lamason, C. and Gong, M., (2007), Optimization of pressing parameters for mechanically surface
densified aspen, Forest Products Journal 57(10) : 64-68.
Rautkari, L., Properzi, M., Pichelin, F., and Hughes, M., (2009), Surface modification of wood using
friction, Wood Science and Technology 43 : 291-299.
Rautkari, L., Properzi, M., Pichelin, F. and Hughes, M., (2010), Properties and set-recovery of
surface densified Norway spruce and European beech, Wood Science Technology 44 : 679-691.
Tarkow, H., Seborg, R., (1968), Surface densification of wood, Forest Products Journal 18:9 : 104–
107.
Cost-Workshop
Technologies and manufacturing equipment for the forming of solid wood
Ulrich Schwarz, Alexander Pfriem
Eberswalde University for Sustainable Development - University of Applied Sciences
Faculty of Wood Technology
Friedrich-Ebert-Strasse 28
16225 Eberswalde, Germany
[email protected]
[email protected]
Key words: wood bending, wood softening, non-cutting shaping
Abstract
The non-cutting shaping of wood is a centuries-old technology. With the application of CNC milling
technology, this kind of forming has almost disappeared. This trend is strengthening implementation of curved
elements in furniture manufacturing. Nevertheless, there are in the Federal Republic of Germany only a few
companies who have mastered this technology.
In various projects at the Eberswalde University for Sustainable Development the non-cutting shaping of solid
wood was investigated.
Generally two ways of shaping are possible. First, after shaping of the components, they will be further
processed. Alternatively, a finished part can be produced that is not additionally treated after shaping.
To reduce the effort, with larger deformation degree, the wood is plasticized. With the plasticization additional
effects in the wood can be achieved. This changes effect also structural changes in the bending part. In addition
to the plasticizing with moisture and heat here also plasticizing by structural changes or radio frequency
technology may be applied [1].
Figure 1: local compression fracture
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In the forming process, the mechanical conditions in the bending part are of particular interest [2]. Early age
was recognized by Prodehl that the bending of the Wood is a complex stress distribution prevails in the
bending part [3]. These stresses affect the deformation and the quality of the bending part.
Woods that were plasticized too heavy prone to local deformations:
•
local compression fractures,
•
local clusters short compression wrinkles,
•
global compression wrinkles,
•
expansion cracks perpendicular or across the grain.
Figure 1 shows a typical local compression fracture. In contrast expansion cracks, as shown in Figure 2, appear
always when the tensile strength is exceeded in the respective operating direction.
Figure 2: Expansion cracks
References
[1]
[2]
[3]
100
Schwarz, U., (2010), Technologien und Fertigungsmittel zur Umformung von Massivholz Teil 1:
Methoden der Plastifizierung, Holztechnologie 61(2): 17-24.
Schwarz U., (2010), Technologien und Fertigungsmittel zur Umformung von Massivholz Teil 2:
Methoden der Umformung. Holztechnologie 61(3): 11-14
Prodehl, A., (1931), Untersuchungen über das Biegen gedämpften Holzes. Dissertation, Sächsische
Technische Hochschule zu Dresden
Cost-Workshop
Mechanical properties of heat treated wood after thermodegradation under
different treatment intensity
Kévin Candelier1, Mounir Chaouch, Philippe Gerardin,
Mathieu Petrissans
1
Laboratoire d’Etudes et de Recherches sur le Matériau Bois, EA 4370 Université Henri Poincaré Nancy 1,
Faculté des Sciences et Technologies, BP 239, 54506 Vandœuvre-lès-Nancy, France
[email protected]
Key words: Heat treatment, mass loss, mechanical properties, treatment intensity, thermodegradation
Abstract
Recently, studies concerning the heat treatment of wood have been developed. The main interest of this
treatment is its low environmental impact: no chemical products are used and several local species of wood can
be used. The treated wood has a better dimensional stability and a better durability against fungal attacks.
Theses new properties are obtained by the reactions of thermodegradation which generate a weak mass loss
(ML) close to 10 %. Moreover, the degradation of several compounds as hemicelluloses induces a decreasing
of the mechanical properties. Indeed, in different studies the module of rupture in bending (MOR) is deeply
modified. For the module of elasticity (MOE) a lowest decreasing is observed. All these studies are realized on
different wood species and for variable treatment intensities. Several parameters are not always referenced,
such as the final temperature and duration of the treatment. Also, the tested wood samples are not still in
accordance with the standards used for the mechanical test. It is very difficult from the literature to
characterize the mechanical modifications of a heat treated wood according to the intensity of treatment.
In this work, the following mechanical properties have been studied: MOR (Module of Rupture) and MOE
(Module of Elasticity) in bending, MOE and limit of elasticity in compression. Theses mechanical properties
are evaluated for different wood species and different treatment temperatures. The results are presented
according to the Mass Loss generated by the thermodegradation, which is a good indicator of the treatment
intensity. The studied wood species are: poplar (Poplar nigra), beech (Fagus sylvatica), ash (Fraxinus
excelsior), mine (Pinus sylvestris) and fir (Abies pectimata). The temperatures of treatment are included
between 180°C and 230°C. The mechanical properties are tested according to EN 408 standard with the
following techniques: 4 points bending, camera analysis.
The first results show (according to the Mass Loss): MOR in bending decreases dramatically; MOE in
bending decreases more slightly; MOE in compression decreases deeply and the limit of elasticity in
compression decrease slightly. These results are mainly independent from the treatment intensity. From these
results it can be possible to conclude that the decreasing of the mechanical properties is generated during the
first part of the heat treatment.
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102
Cost-Workshop
Densified wood in 2- and 3 dimensional molding process
Jörg Wehsener1, Peer Haller2
1
Dresden University of Technology, 01062 Dresden, Germany
[email: [email protected]]
2
Dresden University of Technology, 01062 Dresden, Germany
[email: [email protected]]
Key words: molding, densification, end grain, density, temperature, moisture, recovery
Abstract
The densification of wood leads to a new material with high strain. The material behaviour can be described as
viscoelastic material like foam. After the wood densification we receive more than 50% strain in order of the
compression ratio. The modification procedure can be described in three steps: heating, densification and
cooling. To influence the mechanical properties it is possible to choose the process parameter. The processes
take place in a conventional multistory hot press with. In order to test limited range it was choose different
temperature, moisture, pressure, speed and wood species. Several tests were carried out with wood cubes in
labor conditions. One of the requirements to get a formable material needs a homogenous densification profile.
The cell walls will be folded continuous through the whole cross section. The folded cell walls are not stabile
and it is possible to recover. The process of forming material will use this strain potential. Against the aim of
different working projects to produce a material with high dimensional stability of densified wood, will be
used the deformation as a charged energy inside the wood structure. The densification is required as a first step
to produce a high potential of strain. After the wood processing from the single cube to the end grain board
will be molding the second step of shaping. The new formed board is to dry and to fix in the last step. The
process to use the spring back of wood is possible with high temperature and moisture. The compressed
material could be recovered with a treatment in warm water or under a saturated steam atmosphere. Depends
of the degree of densification is the recovering potential theoretical more than 50% in terms on the densified
material. The objective of several test were to find out the optimal relationship between the process parameter
(degree of densification, moisture, temperature, compression speed), the material properties (density, wood
species, annual rings) and the homogenous strain potential.
Figure 1: molded end grain board with textile reinforcement [1] and with densified cubes [2]
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The aim was to use the high strain from compressed wood for molding process perpendicular to the grain.
During the process it was designed a new biaxial densification device. The densification behavior to analyze
by testing of 11 parameters on more than 300 specimens was carried out. Each cube was stamped with 5 by 5
mm grid of the wooden surface. By using that method it will reduce small inhomogenous areas and the
calculation effort. The grid deformation showed the main displacement of crossing points and the distance of it
can be automatically calculated. The same way was used by the determination of recovery. In general will
recover each densified specimen about to 100%, however the speed can be a parameter of the forming quality.
To investigate the molding potential, it was necessary to determine the optimum of the densification process.
The tests were carried out mainly with three wood species. The moisture content of wood was 8 and 18% or
conditioned in the normal climatic, depends of the testing parameters.
The influence of different parameters will affect the uniaxial as well as the biaxial recovery. The special
investigation described the process parameter, which affected the recover potential in one or two directions. To
use the innovative process was it necessary to find the optimum performance between the material parameter
and the production possibilities. There are two ways to use the recover behaviour of wood: unidirectional
densification to mould hollow wood profiles or to take the bidirectional densification to mould
multidimensional end grain boards. Molded wood profiles and boards are efficiently products to replace wood
in same kinds.
Acknowledgement: This publication is based on a research project which was funded by the Federal Ministry
of Food, Agriculture and Consumer Protection of Germany (Grant Reference No. 22024305 (05NR243).
References
[1]
[2]
104
Weser, Th.; Trümper, W.; Abounaim, Md.; Diestel, O.; Cherif, Ch.; Wehsener, J.; Heiduschke, A.;
Haller, P.; Textile Verstärkungsstrukturen für Holzkonstruktionen; Techtextil 2009; Frankfurt/Main;
16. Juni 2009
Wehsener, J; Haller, P.; Densified wood in moulding process; in Tagungsband: 10th World
Conference on Timber Engineering, Miyazaki, Japan, 2008
Cost-Workshop
Thermo-mechanically (TM) modified beech wood (Fagus silvatica L.)
as a raw material for parquet
Marek Grześkiewicz 1, Agnieszka Kurowska2
1
Warsaw University of Life Sciences SGGW
Department of Construction and Technology of Final Wood Products
159 Nowoursynowska Str.
02-776 Warsaw, Poland
[email protected]
2
as above
Department of Panel Products
[email protected]
Key words: Thermo-mechanically wood modification, densified beech wood, parquets
Abstract
Hot beech wood (Fagus silvatica L.) was compressed perpendicularly to wood fibres in laboratory conditions,
using different parameters, such as: compression level, temperature of press plates and direction of pressing
(radial or tangential), in order to obtain densified wood,. The wood structure and the selected physical and
mechanical properties of modified beech wood were tested. The cross-section of the densified wood was
observed using a FEI (the Quanta 200 model) scanning electron microscope. More micro cracks were noticed
in the case of beech wood pressed in tangential than in radial direction (Fig.2). Density profiles (Fig. 1) were
determined for different parameters of wood pressing, using GreCon Laboratory Density Analyzer (Model
DA-X). Higher temperature of press plates leads to smaller differences in the wood density profile. The
obtained material was tested in terms of hardness for the selected parameters of modification, perpendicularly
to fibres and along the fibres, using Brinell tester CV-3000LBD CV Instruments (Fig. 3). TM wood treatment
significantly increases wood hardness which is important for potential application of this material for parquets
or for top layer floor panels. Properties related to water - wood swelling during cyclic wetting and drying were determined. The results indicate the need to apply an appropriate finish to protect densified wood against
water or to stabilise this new material when applying it for floor materials.
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Figure 1: Density profile of beech wood sample after TM modification. Pressing between plates of press
at the temperature of 1600C. Initial wood sample thickness: 22mm. Average density of tested sample: 1177 kg/m3
Figure 2: Densified beech wood after TM treatment and pressing in tangential direction. Pressing between plates
of press at the temperature of 1600C. Initial sample thickness: 22mm; densified sample thickness: 12 mm
300
240,5
Hardness [MPa]
250
200
109,9
150
100
104,8
45,3
50
0
Control
Perpendicular to wood fibres
Densified
Along wood fibres
Figure 3: Hardness of beech wood after TM treatment and pressing perpendicularly to fibres. Pressing between plates
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Cost-Workshop
of press at the temperature of 1600C. Average density: control: 650 kg/m3, densified: 1067 kg/m3
Acknowledgement: The research project regarding beech wood has been partly financed by the Polish
Ministry of Science and Higher Education in the years 2008-2009, grant no. N N309 298534
References
[1]
[2]
Kutnar A., Kamke F.,A, Sernek M. (2009). Density profile and morphology of viscoelastic thermal
compressed wood. Wood Science Technology, 43, 57-68
Kutnar A., Kamke F.A., (2010), Compression of wood under saturated steam, superheated steam and
transient conditions at 1500C, 1600C and 1700C. Wood Science Technology, published online 08
October 2010
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108
Cost-Workshop
Machinability evaluation of thermally modified wood using the Taguchi
technique
Jacek Wilkowski 1, Paweł Czarniak 2, Marek Grześkiewicz 3
1
Warsaw University of Life Sciences SGGW
Wood Mechanical Processing Department
159 Nowoursynowska Str.
02-776 Warsaw, Poland
[email protected]
2
as above
[email protected]
3
as above
Department of Construction and Technology of Final Wood Products
[email protected]
Key words: thermally modified wood, drilling, specific cutting coefficient, surface roughness
Abstract
Thermally modified wood (TMW) is increasingly being applied for floor materials, balustrades and for top
panels in furniture. Despite of many application of TMW, its properties during machining are not fully
Evaluation of the wood machinability includes an analysis of the various criteria and
understood.
corresponding indicators. These criteria include: tool life, cutting forces and surface quality. Thus,
machinability indicators are: the length of cut, cutting forces, cutting power, torque and surface roughness
parameters. Ockajova [1] reported that cutting power during milling of thermally treated beech and modified
maple (at the temperature of 105°C, duration 1,5 hours) is lower than during cutting natural beech and maple
wood. The effect of heat treatment of hardwood on the specific cutting resistance studied Orłowski and
Grześkiewicz [2]. The oak and ash wood was heated with overheated steam at a temperature of 197°C during 4
hours. Then, the square timber samples were cut on the sash gang saw and cutting power was measured. It has
been found out that thermal modification of ash wood causes a decrease of the specific cutting resistance. In
the case of oak wood this phenomenon was noticed only for small values of feed per tooth. This paper presents
a method for machinability evaluation of modified and unmodified wood during drilling. Two species of wood
were examined: oak and ash. Process of thermal modification in atmosphere of overheated steam consisted of
five stages. Primary modification process in overheated steam at the temperature 165oC in the case of oak
wood and at the temperature 197oC in the case of ash wood. Machinability indicators should be identified with
the optimal cutting parameters. Hence, this paper illustrates the application of Taguchi method using the utility
concept for multi-objective drilling process optimization. Two parameters (feed rate and spindle speed) were
identified. Each parameter was investigated at three levels to study the non-linearity effect of the process
parameters. Array L9 (24) was selected. Machining Center Busellato JET 130 and through drill LEITZ with one
edge made from policrystallic diamond with diameter 10mm was used to perform the experiments. Following
signals were measured: torque, thrust force and surface roughness of the drilled holes. The acquisition of the
torque and thrust force was made by a Kistler piezoelectric dynamometer 9345A (Fig.1). The Surftest SJ201
Mitutoyo was used to measure the surface roughness of the drilled holes (parameters Ra, Ry, Rz). Work pieces
were drilled across fibers. Feed direction was parallel to the annual rings. The value of specific cutting
coefficients related to the thrust force (kF) and torque (kM) was calculated. The analysis of means (ANOM) is
used to determine the optimal parametric settings and it is the process of estimating the main effects of each
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parameter [3]. Thermally modified wood has a higher coefficient kF and lower coefficient kM. The surface
roughness of the modified wood is not significantly different from the roughness of the unmodified wood, this
concerns both oak and ash. The analysis of variance (ANOVA) establishes the relative significance of factors
in terms of their percentage contribution to the response [3]. Results of ANOVA for the specific cutting
coefficient kF and for surface roughness for oak and thermally modified oak were illustrated in Table 1.
Figure 1: Elements of measurement chain
Table 1. Summary of ANOVA for the specific cutting coefficient kF and for surface roughness Ra in the case of oak and
modified oak
Surface roughness Ra
The specific cutting coefficient kF
Degrees
Source of
Sum of
Percent
Sum of
Percent
of
Variance
Variance
variance
squares
contribution
squares
contribution
freedom
OAK
Feed rate
Spindle speed
2
2
41,3350
0,5320
20,6675
0,2660
98,37
1,27
88,2039
8,4558
44,1020
4,2279
83,55
8,01
Error
4
0,1540
0,0385
0,37
8,9101
2,2275
8,44
Total
8
42,0210
5,2526
100,00
105,5698
13,1962
100,00
Feed rate
Spindle speed
Error
2
2
4
38,5897
0,1969
0,2241
19,2949
0,0985
0,0560
98,92
0,50
0,57
41,9712
4,0329
2,9943
20,9856
2,0165
0,7486
85,66
8,23
6,11
Total
8
39,0107
4,8763
100,00
48,9984
6,1248
100,00
MODIFIED OAK
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Cost-Workshop
References
[1]
[2]
[3]
Ockajova, A., (1996), Tool wear versus its tool material and workpiece material. Holz als Roh- und
Werkstoff 54: 105-107.
Orłowski, K., Grześkiewicz, M., (2009), Effect of heat treatment of hardwood on the specific cutting
resistance. Annals of Warsaw Agricultural University – Forestry and Wood technology 69: 147-151.
Phadke, M.S., (1989), Quality engineering using robust design. Englewood Cliffs, NJ: Prentice-Hall:
1-50.
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Cost-Workshop
Mechanical characteristics of aged Hinoki (Chamaecyparis obtusa Endl.) wood
from Japanese historical buildings
-Comparison between naturally aged wood and thermally treated woodMisao Yokoyama1, Joseph Gril*2, Miyuki Matsuo*1,
Junji Sugiyama*1and Shuichi Kawai*1
1
Research Institute for Sustainable Humanoshere, Kyoto University, Japan 611-0011
[email protected]
2
Laboratoire de Mécanique et Génie Civl, Université Montpellier 2, CNRS, France
Key words: naturally aged wood, Hinoki (Chamaecyparis obtusa Endl.), Japanese historical buildings
Abstract
From the ancient times, wood has been used as construction materials, and some wooden buildings
have been preserved for over a thousand years such as Horyu-ji Temple which is one of the oldest
wooden buildings in the world. On the other hand, wood has also been used for various wooden
artifacts like Buddhist statues, and aged ones are handled with highly care, because of their fragile
qualities. It is well known that the properties of wood change over a long period in the environment
after harvesting. Studies about the changes in physical and mechanical properties with elapsed time
have been conducted due to the importance of safe long-term use and as basic studies of wood
science. [1] In a previous paper the author examined he mechanical properties of naturally aged
Hinoki (Chamaecyparis obtusa Endl.) from Japanese historical buildings. Although aged wood
appeared more rigid and stronger than the recent wood, after density and humidity corrections no
clear trend was anymore observed for L and R rigidity, as well as for L strength. The post-linear
behavior, however, was drastically influenced by wood age. Aged wood was brittle, especially in R
direction. [2] And another common effect of aging and thermally treatment is the color change in
the parallel study. [3]
And in the previous and applied study, thermally treated wood were used in the conservation and
restoration of Japanese wooden Buddhist statues. Fig. 1 shows the color changes of Hinoki samples
with thermally treated and restored wooden stature using thermally treated wood.
Hence, comparing the mechanical properties of thermally treated wood with naturally aged wood is
very important to investigate the mechanism and prediction of aging of wood. In this paper, the
specimens were completely dried to avoid the effect of hydrolysis and then treated under the range
of temperature from 90 to 180 °C, well below the thermal decomposition point of wood in dry
condition. Therefore it was expected that just the effect of thermal oxidation on mechanical
properties change was estimated and that it will be possible to predict mechanical properties change
during natural aging where almost only thermal oxidation occurs.
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Figure 1: the color changes of Hinoki samples with thermally treated (a) and
restored wooden statured using thermally treated wood (b).
The trend of mechanical properties of aged Hinoki (Chamaecyparis obtusa Endl.) wood are similar to the
effect of a thermally treatment at 90℃, 120℃, 150℃ and 180℃ were observed. Kohara observed that all these
features are similar in thermally treated wood performed at 130 °C [4].
The general trends might be analogos, quantitative differences are likely to be observed between the various
kinds of modifications induced by age. The relation of the kinetics of identified phenomena with physical and
chemical changes remains to be investigated. Analysis on the time- temperature dependency in each data set of
both naturally aged wood and thermally treated wood is under progress concerning these mechanical
properties. Master curve obtained by shifting individual stress-strain curves and the activation energy delivered
shift factors for each must be investigated further.
Acknowledgement: The authors thank Mr. Mitsuo Ogawa and the owner of the Senjyu-ji temple for obtaining
samples. The research was allowed thanks to a grant by the Japanese Society for the Promotion of Science.
References
[1] Kohara J, Study on the old timber, Research Report of the faculty of engineering, Chiba University 9 (15)
(1958) 1-55 (in Japanese).
[2] Yokoyama M, Gril J, Matsuo M, Yano H, Sugiyama J, Clair B, Kubodera S, Mitsudani S, Sakamoto M,
Ozaki H, Imamura M, Kawai S, Mechanical characteristics of aged Hinoki wood from apanese
historical buildings, Computes Rendus Physique 10(2009) : pp601-611
[3] Matsuo M, Yokoyama M, Umemura K, Gril J, Yano K, Kawai S, Color changes in wood during heating:
kinetic analysis by applying a time- temperature superposition method, Applied physics A
(2010)99:47-52
[4] J.Kohara, H.Okamoto, Study on the old timber – Increasement in Young’s modulus of heat-treated wood,
Mokuzai Gakkaishi 1(2) (1955) 80-84 (in Japanese)
114
Cost-Workshop
Feasibility of wood peeling process assisted by radiant energy.
Anna Dupleis1, Rémy Marcal1, Mark Hughes2
1
Arts&Métiers ParisTech, rue Porte de Paris, 71250 Cluny, France
[email protected]
[email protected]
2
Aalto University School of Science and Technology,
Department of Forest Products Technology, P.O. Box 16400,
00076 Finland
[email protected]
Key words: infrared, microwave, ohmic heating, green-wood heating, radiant energy, peeling, veneer.
Abstract
The peeling process requires green-wood to be heated to temperatures ranging from 50 to 90 °C before
processing. This pre-treatment offers substantial advantages in terms of improving both the yield of veneer and
its quality. This heating treatment is usually done by soaking bolts in water at elevated temperatures. However,
these methods present many drawbacks in terms of energy losses and yield efficiency. This situation calls for
new technological solutions to heating green-wood prior to peeling. In the past, the use of electrical and radiant
energy, such as microwaves (MW), has been investigated as a means of heating wood prior to peeling. Results
have been promising, but have demonstrated the need to examine the suitability of heating systems using
infrared energy (IR) embedded directly on the peeling machine to heat the bolt whilst cutting.
1.
Peeling Process
The peeling process consists of transforming a bolt into veneer using a rotary peeling action (Figure 1).
ω
v
Figure 1: Principle of a rotary peeling machine (a) cross-section view (b) perspective view, [1]
Prior to peeling, the bolt is heated and debarked. The heating increases the wood’s deformability, reducing the
risks of lathe checking and lowering cutting forces and hence power consumption. Bolts are traditionally
heated by immersion in hot water. However this method presents many disadvantages amongst which are the
duration of treatment (12 to 72 hours), poor energy efficiency, huge building requirements, the washing out of
phenolic extractives inducing water pollution and affecting wood’s natural durability and cohesion (risks of
cracks at bolt ends). These problems have highlighted the need for research work to find alternative solutions
to heating green-wood that are applicable within the peeling process.
2.
Electric ohmic heating
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Once crossed by an electric current wood, being a conductor, acts as an electrical resistor which dissipates heat
through the whole material (Joule effect). Experiments performed using an electrical current at a frequency of
50 Hz have demonstrated that this ohmic method enables heating rates 600 times higher than that of soaking to
be attained, whilst the quality of veneers was equivalent [2,3]. However, high voltages (5-10 V/mm in the
longitudinal direction) were required. Due to the variation of wood resistivity with moisture content the current
flows mainly in sapwood, leading to heterogeneous heating. However, ohmic heating has demonstrated that
pre-peeling heating kinetics of wood does not depend on the duration of heating but only on cell wall
temperature (as soon as the cell wall is brought to the required temperature, plasticisation of the lignin starts).
Therefore, investigations have been carried out to develop technologies for heating wood rapidly but
optimising energy consumption.
3.
Radiant energy heating
Among the possible solutions, radiant heating offers a high energetic yield because energy propagates without
any contact with the materials.
3.1 High Frequency Microwave
High-Frequency Microwave (MW) is a developing technology in the heating process of green-wood.
Characterised by a rapid, homogeneous in-depth heating of wood and featuring high energy efficiency, MW
was considered to be an interesting alternative to ohmic heating [4], but the complexity of the technology
requiring covered waveguides makes it impossible to implement directly on the peeling machine.
3.2 Infrared (IR) heating
Experimental results have demonstrated that wood exposed to IR radiation transmits and absorbs energy with
high energetic yield. IR radiation enables heat to be transferred through wood and experiments have indicated
that temperature decreases with increasing penetration into the sample. Under an incident flux of 62 kW/m², a
temperatures increase of 50 to 70 °C in 5 s was obtained in a 1mm thick wood sample [3].
4.
Conclusion and prospective work
Compared to other methods of heating, IR has demonstrated the best suitability in terms of energetic
efficiency, feasibility of implementation and heating kinetics. However, a better understanding of IR heat
propagation in green-wood has to be gained in order to determine the requirements for heating green-wood
prior to peeling. The questions that arise deal with:
- the role played by wood parameters in IR heating kinetics including moisture content, density, species,
heartwood/sapwood, earlywood/latewood, longitudinal/transversal direction;
- the IR radiation parameters influencing wood heating (wavelength, power density, distance to the wood
surface);
- the characteristics of IR heating to optimize the peeling process.
The present study aimed to answer these questions will have for first objective to investigate the required
temperature of the bolt surface portion to be peeled for an efficient peeling process.
References
[1]
[2]
[3]
[4]
[5]
116
Navi P., Heger F., (2005), Comportement thermo-hydromécanique du bois: applications
technologiques et dans les structures. PPUR presses polytechniques.
Lutz F., (1960), Heating veneer bolts to improve quality of douglas-fir plywood.
Marchal R., Gaudillière C., Collet R., (2004), Technical feasibility of an embedded wood heating
device on the slicer or the peeling lathe, in Proceedings 1st International Symposium “Veneer
Processing and Products”.
Torgovnikov G., Vinden P., (2009), Microwave wood modification technology and its applications,
Forest Products Journal 60(2) :173-182.
CETIAT, (2003), Caractérisation du chauffage déroulé par infrarouge de bois déroulé, 48 p.
Cost-Workshop
Fracture mechanics characteristics of welded joint of wood
Martin Rhême1, John Botsis2, Joël Cugnoni2, Parviz Navi1
1
Bern University of Applied Sciences, Material and Wood Technology
Solothurnstrasse 102, CH-2500 Biel
2
Laboratory of Applied Mechanics and Reliability, Ecole Polytechnique Fédérale de Lausanne
LMAF–STI–EPFL, Station No 9, CH – 1015 Lausanne, Switzerland
Key words: Welding of wood, Energy release rate, Fracture, Beech
Abstract
The welding of wood is an assembling technique without any addition of adhesive. Technology for such
assembling technique is based on the friction welding. During welding, the increase of temperature induces
some changes in the wood chemical and physical properties. Gfeller et al. [1] showed that the joint was made
of wood fibres embedded in a lignin and other wood component matrix. Welding of wood offers a very fast
and environmental friendly technique to assemble wood pieces. Chemical and physical changes induced by the
welding process have been intensively investigated [1, 2]. The densification process in the joint vicinity has
also been observed with different microscopic means [3].
In addition to many studies of the shear mechanical properties of the joint [1, 3], first attempts to study the
welded joint with fracture mechanics have been carried out by Ganne-Chédeville et al. [4] and latter by
Omrani et al. [5]. It appears that the mechanical properties of the welded joint are highly dependent on the
process parameter and on the wood’s species and orientation. Furthermore, the interaction of a welded piece
with moisture leads to a considerable decrease of the shear strength, sometimes even opening of the joint
without external loads.
It is assumed that the fracture of a welded joint is due either to the decaying of the properties of the joint
material or to the strong stresses concentrations due to hygro-expansion of the wood. Thus experimental and
theoretical works are needed to determine to what extent each of these mechanisms participate in the fracture
of the joint subjected to moisture variation and external load. In this work, the fracture characteristics of
welded pieces at different uniform moisture content are experimentally characterised. The data will serve to
construct a numerical model of fracture of the interface. Welded pieces are considered as a layered composite
material with interlaminar crack propagation.
Figure 2 Experimental setup of the DCB test
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In particular, two beech pieces (300x30x5 mm3) are welded together. The initial crack is induced by covering a
100x30 mm2 surface area of the pieces with grease, thus avoiding friction and bonding. Before welding, the
wood is placed in a normal climate (20°C/65%RH) until equilibrium. The width of the specimens is afterward
reduced to 25 mm and the lateral faces are coated with brittle white paint.
A DCB test is performed to determine the Mode I fracture characteristics. Displacement-force data are
recorded during the test along with pictures of the lateral face of the specimen to track the crack front. Three
reduction methods are used to determine the fracture toughness of the laminate
A typical Load – Displacement curve is presented in figureFigure 3. The data of the load displacement curves
and the picture showing the position of the crack at onset enable to determine values of GIc according to the
crack length. Results of the specimen acclimatized in a normal climate are presented in figureFigure 3.
a
b
c
Figure 3 Treatment of the DCB test's data with a compliance calibration reduction method. a) Selection of point at
crack onset. b) Fitting compliance evolution with power law. c) Computation of Fracture toughness with the help of
the compliance expression
The load – displacement curve shows stable but not smooth crack propagation. This is certainly due to joint
inhomogeneity, but the visual inspection lead under optical microscopy could not link the fracture profile
feature with the “jumps” observed during the test. The three reduction methods give similar results. The values
of fracture toughness obtained are coherent with those measured in [4]. This procedure for characterization of
the fracture in wood welded joint seems to be appropriate and will be used in further test coupled with the
influence of the moisture content of the specimen.
References
[1]
[2]
[3]
[4]
[5]
118
B. Gfeller, M. Zanetti, M. Properzi, A. Pizzi, F. Pichelin, M. Lehmann, and L. Delmotte. Wood
bonding by vibrational welding. Journal of Adhesion Science and Technologie, 17:1573–1589, 2003.
L. Delmotte, C. Ganne-Chedeville, J.M. Leban, A. Pizzi, and F. Pichelin. CP-MAS, 13C NMR and
FT-IR investigation of the degradation reactions of polymer constituents in wood welding. Polymer
Degradation and Stability, 93:406–412, 2008.
C. Ganne-Chédeville. Soudage linéaire du bois: étude et compréhension de modifications physicochimiques et développement d’une technologie d’assemblage innovante. PhD thesis, Universtié
Henri Poincaré, 2008.
C. Ganne-Chédeville, G. Duchanois, A. Pizzi, F. Pichelin, M. Properzi, and J.M. Leban. Wood
welded connection: energy release rate measurement. Journal of Adhesion Science and Technology,
22:169–179, 2008.
P. Omrani, H.R. Mansouri, G. Duchanois, and A. Pizzi. Fracture mechanics of linearly welded wood
joints: effect of wood species and grain orientation. Journal of Adhesion Science and Technology,
23:2057–2072, 2009.
Cost-Workshop
An impact device designed to assess the grindability of heat treated wood
Floran Pierre, Giana Almeida and Patrick Perré
AgroParisTech, UMR1092, LERFoB, Wood Biomaterial Biomass Team, ENGREF,
14 rue Girardet 54042 Nancy, France
Key words: pretreatment, grindability, impact test, Maritime pine, Pedunculate oak.
Abstract
Today, energy from biomass is promoted as part of possible solutions to the rarefaction of fossil energy and to
global warning. Followed by a Fisher-Tropsch synthesis, biomass gasification is a possible way to produce
biofuels. Nevertheless, a preconditioning is needed, since the physicochemical properties of the raw biomass
are not suitable for a direct use in a gasifier. In particular a grinding step of biomass is necessary. Middle heat
treatment (temperature level below 300°C) is among possible pretreatments. This presentation is more
specifically focused on the mechanical modification of heat treated wood.
Maritime pine (Pinus pinaster) and pedunculate oak (Quercus robur) were used in this study. Heat treatment
was performed using a new experimental device [1] at different treatment intensities. Three temperature levels
(220, 250 and 280°C) and two durations (1 and 5h) were chosen for this purpose. The final sample dimension
used in mechanical tests was of 10×10×10 mm3. In order to minimize the wood variability, successive samples
were cut along the longitudinal direction.
The modification of mechanical properties caused by heat treatment was first evaluated using low compression
rates. However, to be closer to the grinding conditions, an impact device was designed to evaluate the
mechanical behaviour of wood at high compression rates. All samples were tested in radial direction.
Our results show that the loss of mechanical strength caused by the heat treatment improves its grindability
and eases its transformation into small particles, suitable to be injected into a gasifier. More precisely, our
results indicate that the heat treatment decreases the wood stiffness and the maximal compression stress. For
pine wood the stiffness is decreased by 53 % whereas the maximal compression stress is decreased by 62% for
the most intense treatment (280°C, 5 h). The compression plateau of treated sample depicts successive peaks
with a higher frequency and lower amplitude than the one of untreated sample showing that brittleness is
increased (figure 1). This brittleness will be quantitatively evaluated in further works, because this is certainly
a relevant criterion concerning grindability. Images taken by a high-speed camera during impact test illustrate
these points (figure 2).
The comparison between quasi-static compression test and dynamical compression test exhibits a dramatic
effect of the deformation rate on the mechanical behaviour of wood. For both untreated and treated samples,
our results show that the stiffness increases with the increase of deformation rate. For pine it is increased by
25% for untreated sample and by 51% for treated sample, when the deformation rate increase from 1mm/min
to 1m/s. Treated wood is more affected by the deformation rates. Contrary to the smooth curves observed for
native wood in the case of quasi-static loading, the compression plateau present now several peaks, related to
ruptures of the cellular structure. At high compression rates, native wood presents a brittle behaviour (figure
3).
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25
Stress (MPa)
20
σel max = 13.5 MPa
σcomp max = 19 MPa
280°C; 5h
Untreated
A)
15
σel max = 7 MPa
σcomp max = 7.1MPa
10
B)
5
0
0
40
20
Figure 2. Deformation of pine wood during the
impact. Untreated (A) and heat treated (B) sample.
60
Strain (%)
Figure 1. Radial compression of untreated and heat
treated pine during the impact.
20
60
A)
B)
V=10mm/min
V=1mm/min
V=1m/s
Stress (MPa)
Stress (MPa)
40
V=1m/s
V=10mm/min
V=1mm/min
15
10
20
5
0
0
40
20
60
0
0
Strain (%)
60
30
90
Strain (%)
Figure 3. Influence of the deformation rate on the grindability behaviour of pine wood. Untreated (A) and
heat treated sample (B).
References
[1]
120
Colin, J., Rémond, R., Perré, P. 2008. Mise au point d’un four de traitement thermique et étude
de la pyrolyse ménagée du bois. Actes séminaire RP2E.
Cost-Workshop
Comparison between accelerated thermo-hydro aged wood and naturally
aged wood.
Julien Froidevaux1,2, Thomas Volkmer1, Joseph Gril2, Marco Fioravanti3,
Parviz Navi1
1
2
Bern University of Applied Sciences, Architecture, Wood and Civil Engineering
[email protected]
Université de Montpellier II, Laboratoire de Mécanique et Génie Civil, Mécanique de l'Arbre et du
Bois
3
DEISTAF – University of Florence, Italy
Key words: accelerated aging, micro-mechanics, thermo-hydro treatments.
Abstract
The effects of aging in wood in term of physical, mechanical and chemical degradation has been studied
first by Jiro Kohara [1] and more recently by Erhardt et al. [2-3] and Obataya [4]. It has been observed
that similar degradation can be found in thermo-hydro (TH) treated wood [4]. The aim of this study is to
compare the mechanical behavior of naturally aged and accelerate TH wood in the radial direction.
A first pressure vessel with controllable temperature, oxygen pressure and relative humidity has been
designed and constructed. The temperature and relative humidity range are 100 to 150 °C and 2 to 100%
of RH respectively. This pressure vessel is able to maintain the conditions constant for long term
processing. A second pressure vessel, using a vapor heating system, has been used to test higher
temperature range (120 to 200 °C). The amount of oxygen cannot be set in this last thermal cell.
Different types of thermo-hydro treated wood have been done with these machines.
Figure 1: Mean radial Young's modulus of sound, old and accelerated TH aged wood measured at 23°C and 76 % RH.
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Figure 2: Mean radial yield stresses of sound, old and accelerated TH aged wood measured at 23°C and 76 % RH.
Preliminary results indicate that in general the radial Young's modulus of natural aged wood does not
modify extremely, as it can be seen on figure 1. However, the yield stress shows a decrease of about 25%
(figure 2). Similar decrease of the yield stress has been shown on treated wood at 130°C, 5% of RH and
under vacuum pressure for different time from 1 to 7 days. The coloration of the treated woods seems
also to be similar to the naturally aged wood. However, the thermally treated woods show an important
decrease of the radial Young's modulus.
Some micrographs have been prepared in the tr plane. It has been seen some localized damages in the
structure of old and accelerated TH wood which could reduce the fracture properties. Such damages have
not been seen in such quantity in the sound woods.
Acknowledgement: The financial support of the Swiss National Science Foundation (FNS) under the
project K-21K1-122336/1 is acknowledged with gratitude.
References
[1]
[2]
[3]
[4]
122
Kohara J, Studies on the durability of wood I, mechanical properties of old timbers, Bulletin of
Kyoto Prefectural University, vol. 2, 1952, p. 116-131 (In Japanese).
Erhardt, D., Mecklenburg, M. F., Tumosa, C. S. and T. M. Olstad, "New vs Old Wood:
Differences and Similarities in Physical, Mechanical, and Chemical Properties". ICOM
Preprints, 11th Triennial Meeting, Vol. 2, 903-910 (1996).
Erhardt, D. and M. Mecklenburg, "Accelerated vs Natural Aging: Effect of Aging Conditions
on the Aging Process of paper". Material Issues in Art and Archaeology IV, Vol. 352, (1995)
247-270.
Obataya, Eiichi (2007): Characteristics of aged wood and Japanese traditional coating
technology for wood protection, in: Acte de la journée d'étude Conserver Aujourd`hui: Les
"Vieillissements" du Bois, Cité de la musique, pp. 26-44.
Cost-Workshop
Modelling of colour change induced by aging and heat treatment by using
the multi-process kinetic analysis
Miyuki Matsuo*1, Joseph Gril2, Misao Yokoyama1, Kenji Umemura1,
Shuichi Kawai1
1
Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji, Kyoto, Japan.
*[email protected]
2
Laboratoire de Mécanique et Génie Civil, Université Montpellier 2, CNRS, CC 048 Place
Eugène Bataillon, 34095 Montpellier Cedex 5, France
[email protected]
Key words: colour change, accelerated aging, natural aging, kinetic analysis, historical buildings
Abstract
Colour of wood changes both during natural aging and during heat treatment. Colour measuring, which
is non-destructive and requires only a small area, might be an useful tool as an aging or deterioration
index. Exact modelling of colour changes is important not only to predict deterioration but also to
understand the aging and deterioration mechanism of wood. This study deals with the modelling of
colour changes that occur both during natural aging and during heat treatment by using kinetic analysis.
For better understanding of the process of colour change, we employed multi-process kinetic analysis.
Hinoki (Chamaecyparis obtusa Endl.), which is a typical species used for historical buildings and
Buddhist sculptures in Japan, was used. Naturally aged wood specimens were prepared from the
members of historical buildings built in from 7th century to 15th century. Namely, the aging time ranged
from approximately 550 years to 1600 years [1][3]. The specimens for heat treatment were prepared
from the wood harvested in 1988. Completely-dried specimens were treated at 90°C, 120°C, 150°C, and
180 °C. The treatment duration ranged from 0.5 hours to approximately 2 years [2]. The colour of the
specimens was measured with a spectrophotometer (KONICA MINOLTA CM-2600d) and was
expressed by CIELAB colour parameters (L*, a*, and b*). Figure 1 shows the examples of the colour
change during natural aging and heat treatment.
Figure 1: Colour change of hinoki wood during natural aging and during heat treatment. (a) wood harvested in 1998
as a control, (b) aged in the ambient condition for 750 years; (c) for 1600 years, (d) treated at 180°C for 2 hours; (e)
for 12 hours.
When modelling colour changes induced by natural aging and heat treatment, we assumed that the
change of a colour parameter x can be decomposed as
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x = x0 + x1 + ... + xN
(1)
where x0 represents the initial colour value before natural aging or heat treatment, xk (k>0) are variation
of x related to independent chemical or physical processes. Each xk starts from 0 in the initial state and
approaches a limiting value Xk following a first-order kinetic;
xk(t) = Xk[1 - exp(-t/aT)] (k = 1 .. N)
(2)
where t is aging or treatment time and aT is a time-temperature dependent shift factor at the aging or
treatment temperature T. We chose N = 3 on a trial basis because the trend of colour changes indicated
that at least 3 processes of the reactions occurred; i.e. the change of a colour parameter x can be
expressed as follows:
(3)
x(t) = X1[1 - exp(-t/aT)] + X2[1 - exp(-t/aT)] + X3[1 - exp(-t/aT)] .
The apparent activation energies for each process were calculated.
The models calculated well fitted with the measured colour changes in all colour parameters, L*, a*, and
b*. The modelled and measured value of L* is shown in Fig. 3 as an example. The calculated activation
energies for the first, second, and third process were 130, 109, and 135 kJ/mol, respectively. The
successful modelling and the calculated kinetic parameters will bring important information about the
behaviour of colour during aging and heat treatment.
80
Natural
aging
A
70
120°C
T 120
60
180°C
T 180
50
Model-90°C
T 90
40
Model-150°C
T 150
90°C
T 90
L*
150°C
T 150
Model-natural
aging
A
Model-120°C
T 120
Model-180°C
T 180
30
-2
-1
0
1
2
3
4
logt (hour)
5
6
7
8
Figure 2:Measured colour value L* of natural aging wood and heat treated wood and the models produced by kinetic
analysis considering 3 first-order processes.
Acknowledgement: This work was supported by a Grant-in-Aid for Scientific Research (A) (No.
20248020) and for JSPS Fellows (No. 21⋅2994) from the Japan Society for the Promotion of Science. A
part of this work was presented in Wood CulTher COST IE0601 Symposium in Braga (2008) and in
Hamburg (2009).
References
[1]
[2]
[3]
124
Yokoyama, M., Gril, J., Matsuo, M., Yano, H., Sugiyama, J., Clair, B., Kubodera, S.,
Mistutani, T., Sakamoto, M., Ozaki, H., Imamura, M., Kawai, S. (2009) Mechanical
characteristics of aged hinoki wood from Japanese historical buildings, C. R. Phys. 10(7):60111.
Matsuo, M., Yokoyama, M., Umemura, K., Gril, J., Yano, K., Kawai, S., (2010), Color
changes in wood during heating: Kinetic analysis by applying a time-temperature superposition
method, Appl. Phys. A 99(1):1-6.
Matsuo, M., Yokoyama, M., Umemura, K., Sugiyama, J., Kawai, S., Gril, J., Kubodera, S.,
Mitsutani, T., Ozaki, H., Sakamoto, M., Imamura, M., Aging of wood - Analysis of color
changes during natural aging and heat treatment -, submitted to Holzforschung
Cost-Workshop
The development of commercial modified wood processes – the Plato
process
Edo Kegel1 and Dennis Jones2
1
Marketing Dept, Plato International BV, Arnhem, Netherlands
email: [email protected]
2
Woodknowledge Wales, BRE Wales, Engineering Centre for Manufacturing and Materials (ECM2),
Heol Cefn Gwrgan, Margam, Neath Port Talbot SA13 2EZ, UK
email:[email protected]
Key words: commercialisation, marketing, business development, modification
Abstract (Times New Roman, bold, 10 pt, center)
The importance of marketing the right product has gained importance in the wood modification sector.
No longer can modified wood just depend on “being better than other materials”. There needs to be a
greater awareness of client and customer perception, as well as financial considerations.
The development of a commercial process depends not only on there being a guaranteed or developing
market for the modified material, but also the engineering logistics in converting small scale production
to large scale. There needs to be a thorough understanding of the process thermodynamics, waste and
effluent removal, re-use and/or disposal, as well as ensuring long-term hardware stability and operation.
This paper will deal with some of the issues experienced by Plato International, one of the longest
standing wood modification companies in Europe. The Plato process, based on the hydrothermal
processing of timber has become established in a range of product ranges.
More recent development has seen discussions into the expansion into new markets, such as Portugal,
where the market tends to favour tropical timber, so there are great benefits to be gained by providing a
stable alternative based on European species.
.
The paper will focus on:
•
Processing and commercialization – what had to be done to develop good lab-based results
into a financially feasible commercial process
•
Marketing/ promotion - focussing on today’s market issues.
•
Examples of real products in real uses – proven track records
•
Environmental considerations – what clients and customers really want
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126
Cost-Workshop
Wood surface densification using different techniques
Lauri Rautkari1, Mark Hughes2
1
Aalto University
Department of Forest Products Technology
[email protected]
2
Aalto University
[email protected]
Key words: densification, modification, surface
Abstract
It is well known that wood density correlates with its mechanical properties. Wood can be compressed
when above its glass transition temperature, without breaking the cell walls. Wood is a porous material
and, in theory, can be rather easily compressed until the density reaches that of the cell wall material
(~1.50 g/cm³) [1]. Wood softens when it is heated, with the lignin, hemicellulose and cellulose
displaying different softening behavior depending upon the temperature and moisture content [2-3].
The greatest difference between surface densification and bulk densification is that in the bulk
densification process both surfaces are heated, thus both sides are compressed. The surface densification
process starts with relatively dry wood; in most of the studies the moisture content of the wood has been
~12 % [4-7]. Therefore, the densification process is relatively fast; only some minutes or even seconds.
The processing time is also dependent on the initial moisture content.
Surface densification can be performed in different ways. One way is batch compressing, which is a well
studied method of wood densification. However, usually the studies using this approach concern bulk
densification and not surface densification. In surface densification only the surface of the wood is
heated and compressed in press heated on one side [8,9] or in a continues press with an endless belt [10].
Results show that a product’s mechanical properties are correlated with the degree of compression. There
are differences between bulk compressing and motion compressing, for the product. Motion compressing
means friction movement on the surface during compressing. Batch compression without motion allows
canal resin to migrate to the surface, making spots, however, using motion the canal resin might be
spread over the surface. Compression with motion gives a very smooth surface when heated rollers are
used for surface densification [11,12]. Also the glossiness is increased, indicating a smooth surface [5].
Surface hardness is increased, depending on the degree of compression [4-6]. Wettability is also
decreased depending on the degree of compression [4,7]. Alternatively, surface modification of solid
wood can be produced by laminating untreated low density wood with a high density wood. A thin layer
of densified wood can be laminated onto untreated wood, to improve the properties of the material. This
modification method has been presented in several publications [13-15].
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Surface densified wood springs back in humid conditions [7]. The elimination of the so-called “setrecovery” with heat treatment after densification, is well studied. Various studies on compressed solid
wood [16-18] have, however, reported that set-recovery, can be totally or almost totally eliminated if a
high temperature (180-200 ºC) post treatment is carried out, particularly in a closed press system under
humid conditions. It has been reported [18-19] that the minimum post-treatment time is about 6 minutes,
at a RH of 100 % and 200 ºC temperature. These high humidity/temperature conditions are only possible
in a closed system with high steam pressure [20]. It is possible to eliminate the inner stresses by heating
without steaming alone, but then the process time is much longer. It is possible to eliminate set-recovery
using a steam heat-treatment at 1 ATM, when the steam injection starting point temperature is at least
higher than 100 ºC, to avoid high relative humidity, thus set-recovery already during the heat-treatment
process [21].
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
128
Kellog R., M., Wangaard F., F., (1969), Variation in the cell-wall density of wood, Wood and
Fiber Science 1(3) : 180-204.
Hillis, W., Rozsa, A., (1978), The softening temperatures of wood, Holzforschung 32 : 68-73.
Salmén, L., (1990), On the interaction between moisture and wood fibre materials. In:
Proceedings of Materials Research Society Symposium U.
Pizzi, A., Leban, J-M., Zanetti, M., Pichelin, F., Wieland, S., Properzi, M., (2005), Surface
finishes by mechanically induced wood surface fusion, Holz als Roh- und Werkstoff 63 : 251255.
Rautkari, L., Properzi, M., Pichelin, F., Hughes, M., (2008), An innovative thermo
densification method for wooden surfaces, In: Proceedings of 10th World Conference on
Timber Engineering.
Rautkari, L., Properzi, M., Pichelin, F., Hughes, M., (2009), Surface modification of wood
using friction. Wood Science and Technology, 43 : 291–299.
Rautkari, L., Properzi, M., Pichelin, F., Hughes, M., (2010), Properties and set-recovery of
surface densified Norway spruce and European beech, Wood Science and Technology 44 :
679-691.
Inoue, M., Norimoto, M., Otsuka, Y., Yamada, T., (1990), Surface compression of coniferous
wood lumber II, Mokuzai Gakkaishi 37(3) : 227-233.
Lamason, C., Gong, M., (2007), Optimization of pressing parameters for mechanically surfacedensified aspen, Forest Products Journal 57(10) : 64-68.
Tarkow, H., Seborg, R., (1968), Surface densification of wood, Forest Products Journal 18(9) :
104-107.
Rehm, K., Raatz, C., (2005), Developing of dust-free finishing process for the industry. In:
Proceedings of the 17th International wood machining seminar.
Fuchs, I., Raatz, C., Peter M., Pflüger, T., (2007), Thermo-mechanical processing of wood
materials and effect on the surface roughness. In: Proceedings of Third International
Symposium on Wood Machining.
Kutnar, A., Kamke, F., A., Sernek, M., (2008), The mechanical properties of densified VTC
wood relevant for structural composites, Holz als Roh- und Werkstoff 66(6): 439–446.
Kamke, F., A., Rautkari, L., (2009), Modified wood veneer for structural applications, In:
Proceedings of the 4th International Symposium on Veneer Processing and Products.
Rautkari, L., Kamke, F., A., Hughes, M., (2010), Potential error in density profile
measurements for wood composites, European Journal of Wood and Wood Products DOI:
10.1007/s00107-010-0419-9.
Cost-Workshop
[16]
[17]
[18]
[19]
[20]
[21]
Inoue, M., Norimoto, M., Tanahashi, M., Rowell, R., (1993), Steam or heat fixation of
compressed wood, Wood and Fiber Science 25(3) : 224 - 235.
Navi, P., Girardet, F., (2000), Effects of Thermo-Hydro Mechanical Treatment on the Structure
and Properties of Wood, Holzforschung 54 : 287-293.
Morsing, N., (1997), Densification of wood. The influence of hygrothermal treatment on
compression of beech perpendicular to the grain. PhD thesis. Department of Structural
Engineering and Materials, Technical University of Denmark.
Heger, F., Groux, M., Girardet, F., Welzbacher, C., Rapp, A., Navi, P., (2004), Mechanical and
durability performance of THM-densified wood. Final workshop COST action E22
“Environmental optimisation of wood protection”.
Simpson, W., Rosen, H., (1981), Equilibrium moisture content of wood at high temperatures,
Wood and Fiber 13(3) : 150-158.
Rautkari, L., Hughes, M., (2009), Eliminating set-recovery in densified wood using a steam
heat-treatment process, In: Proceedings of the 4th European Conference on Wood modification.
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130
Cost-Workshop
Influence of the moisture content on the shear strength of welded woodto-wood connections
B. Stamm1, Y. Weinand, B. Hahn2, G. Rossmaier
1
Ecole Polytechnique Fédérale de Lausanne ENAC-IBOIS
[email protected]
2
Ecole Polytechnique Fédérale de Lausanne ENAC-IBOIS
[email protected]
Key words: spruce wood, friction welding, connection, shear strength, moisture, deformation,
temperature
Abstract
Friction welding of wood is an innovative process, able to join pieces of wood without additional
adhesives. Because of its hygroscopic properties, the wood matrix absorbs humidity at the surface from
the surrounding atmosphere. Its moisture content is strongly dependent on ambient conditions and
seasonal changes.
Former research showed that after samples passed a certain moisture content threshold, the creation of
welded wood-to-wood connections becomes difficult and shear strength is significantly reduced.
Tests carried out on spruce samples with different moisture content should help to spot the limits of the
materials moisture content, regarding the feasibility of establishing a welded wood-to-wood connection,
but also to calculate which conditions lead to the most solid welded joints. If specific moisture content is
needed to gain a satisfactory weld, this will have an impact on the storage conditions of the pieces to be
welded.
Figure 1: dimensions of the welded samples
Test series (12 samples each, dimensions according to Figure 1) with three different moisture contents
(0%, 9% and 12%) were welded. Young’s modulus of wood decreases with increasing moisture content
and the material becomes softer. This effect leads to an increase in compression of the sample. The
welding displacement, the sum of a displacement due to compression and a displacement due to
decomposition, is the stop criteria for the process. It is a function of the amount of thermally modified
material forming the interfacial adhesive layer. This has to be increased with increasing moisture content
to reach a satisfactory weld. For the three moisture contents the welding displacement was varied in 0.25
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mm steps (0%: 1 – 1.5 mm; 9%: 2.5 – 3 mm; 12%: 3 – 4 mm), in the ranges which gained the best results
for each particular moisture content.
The samples were analysed with regard to the shear strength of the connection. The results indicate that
moisture could have, contrary to former findings, a negative effect on the shear strength of the welded
connection. Oven dried wood showed 44% better results for interfacial shear strength (5.1 MPa), when
compared with moist samples (maximum value of 2.7 MPa). Standard deviation is also more even for
dry samples.
Figure 2: Shear strength of the test series (12 samples each) as a function of the moisture content
It is not yet clear, how and to what extend the presence of humidity can harm the process. During friction
welding, temperatures reach values of over 400°C. At this temperature, water evaporates immediately
and leaves the interface together with the smoke, or is driven into the cell structure. The high temperature
is beneficial for chemical reactions between the different compounds forming the wood matrix.
Further tests should show at which threshold the water starts to influence the formation of the welded
connection.
For the future application of this technology, welding of wood with low moisture content will lead to
deformation by swelling during the adaptation to the actual ambiant moisture content of the location,
where it is employed. The resultant stresses provoke cracks at the weld, which is quite brittle.
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References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
Ahuja, P., Kumar, S., Singh, P.C., (1996), A model of primary and heterogeneous secondary
reactions of wood pyrolysis, Chem. Eng. Technol. 19: 272-282
Gfeller, B., Pizzi, A., Zanetti, M., Properzi, M., Pichelin, F., Lehmann, M., Delmotte, L.,
(2004), Solid wood joints by in situ welding of structural wood constituents, Holzforschung 58:
45-52
Illing, S., (2002), Untersuchung des Verfahrens und der Produkteigenschaften beim PyrolyseSchweißen von Holz durch Reibschweißen. Diploma Thesis EPFL-IBOIS
Leban, J.-M., Pizzi, A., Wieland, S., Zanetti, M., Properzi, M., Pichelin, F., (2004), X-ray
microdensitometry analysis of vibration-welded wood. Journal of Adhesion Science and
Technology 18: 673-685
Möhler, K., Maier, G., (1969), Der Reibbeiwert bei Fichtenholz im Hinblick auf die
Wirksamkeit reibschlüssiger Holzverbindungen, Holz als Roh- und Werkstoff 27: 303-307
Stamm, B., Windeisen, E., Natterer, J., Wegener, G., (2005), Thermal behaviour of
polysaccharides in wood during friction welding, Holz als Roh- und Werkstoff 63: 388-389
Stamm, B., Natterer, J., Navi, P., (2005) Joining of wood layers by friction welding, Journal of
Adhesion Science and Technology 19: 1129-1139
Stamm, B., (2005), Development of friction welding of wood – physical, mechanical and
chemical studies, PhD thesis no. 3396, Ecole Polytechnique Fédérale de Lausanne
Ganne-Chédeville, C., Properzi, M., Leban, J.-M., Pizzi, A., Pichelin, F., (2008), Wood
Welding: Chemical and physical changes according to the welding time, Journal of Adhesion
Science and Technology 22: 761-773
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134
Cost-Workshop
Studies on self-bonded plywood
Jussi Ruponen1, Lauri Rautkari2, Mark Hughes3
1
Aalto University
[email protected]
2
Aalto University
[email protected]
3
Aalto University
[email protected]
Key words: auto-adhesion, binderless bonding, plywood, self-bonding, veneer
Abstract
Traditionally plywood is produced by cross-laminating wooden veneers using an adhesive to bond the
veneer layers together. However, plywood can also be manufactured from rotary-cut veneers, without
any additional adhesives. This novel, fossil resource adhesive free way of fabricating plywood applies
the same method as utilised since 1930s in the manufacture of hardboard and softboard: a proper
moisture content for the raw material, a high enough temperature and a high enough press pressure. The
method can be termed auto-adhesion, self-bonding or binderless bonding. By these means various
chemical bond types are formed between the veneers layers, e.g. covalent, hydrogen and van der Waals
bonds. It is also found out that greater bond integrity is obtained when the veneers are positioned parallel
to each other. [1-2,5]
This method was utilised within two studies where 5 ply Norway spruce plywood (Picea abies, L.) and 8
ply birch plywood (Betula pendula, L.) were manufactured. The veneers were rotary cut and the veneer
thicknesses were 3.5 mm for spruce and 1.5 mm for birch. Due to the high pressure applied, 6 MPa, the
final board thicknesses varied significantly from the nominal thicknesses of the lay-ups in both cases.
Following hot pressing the plywood underwent considerable compression, making its properties
comparable with the properties of compressed wood. As compressed wood can be stabilised
dimensionally with certain thermal treatments, the same method was studied to see if it could stabilise
binderless bonded plywood as well. Previously, it was shown that self-bonded plywood suffers from
dimensional instability as well as delamination when exposed to moist conditions. [3-4,7]
Considering the moisture exposure test thermally treated as well as untreated specimens were immersed
in water, and their bond integrity was observed as a function of time for the first 150 hours immersion.
The tests provided promising results considering an enhancement in the wet stability of self-bonded
plywood due to a post-manufacture thermal treatment. However, not all types of self-bonded plywood
were successfully enhanced by thermal post treatment, the original manufacturing method was found to
be important. Still, it is possible that another type of a post-manufacture thermal treatment could enhance
the wet stability of these specimens. [6]
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120
100
Aht
80
Aut
Bht
60
But
Cht
40
Cut
20
0
0
20
40
60
80
100
120
140
160
Soaking hours
Figure 1: Bond integrity degree results (%) from the water immersion test for the 5 ply spruce plywood. The three
upmost point groups refer to heat-treated (ht) specimens, whereas letters A, B and C to certain kind of plywood, [6]
References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
136
Cristescu, C. (2006). Bonding of laminated veneers with heat and pressure only. Proceedings
of the 2nd international conference on environmentally compatible forest products “Ecowood”.
Porto, Portugal : 339-348.
Cristescu, C. (2008). Bonding Veneers Using Only Heat and Pressure: Bending and Shear
Strength. Licentiate’s thesis, Luleå University of Technology, Skellefteå, Sweden.
Navi P., Heger F. (2004). Combined densification and thermo-hydro-mechanical processing of
wood. MRS Bulletin 29(5): 332-336.
Okuda, N. and Sato, M. (2006). Water resistance properties of kenaf core binderless boards.
Journal of Wood Science, 52 : 422-428.
Okuda, N. and Sato, M. (2007). Finely milled kenaf core as a natural plywood binder.
Holzforschung, 61 : 439-444.
Ruponen, J., Rautkari, L. and Hughes, M., (2010), Proceedings of the Fifth European
Conference on Wood Modification ECWM5 : Enhancing the properties of plywood produced
by auto-adhesion.
Viitaniemi, P., Jämsä, S., Kontinen, P. and Ek, P. (2002). Menetelmä puristettujen
puukappaleiden valmistamiseksi. Finnish Patent No. FI 110241 B.
Cost-Workshop
Study of impregnation of green wood by specific elastomer – Thermohydro-mechanical behavior of wood/elastomer composite.
Anne Lavalette1, Régis Pommier1, Patrick Castera1, Michel Danis2
1
US2B/ESB, Unity of Wood Sciences and Biopolymers (CNRS/INRA/University Bordeaux1, Cestas,
France) / Academy of Wood Science and technology, Nantes, France
2
LGM2B, Laboratory of material mechanics, Talence, France
Key words: Thermo-hydro-mechanical behavior – wood reinforcement – green gluing
Abstract
Wood is a porous, hygroscopic material which absorbs and desorbs moisture as a result of changes in
humidity. The influence of moisture on the strength properties and wood swelling/shrinking is
substantial.
Traditional wood panels are made from dried veneers. A recent study based on a new Polyurethane
adhesive revealed that wood panels can be green glued.
Following this technological development, the Polyurethane absorption in green wood and related
mechanisms has been investigated, as well as chemical and mechanical reinforcements. Experimental
investigations such as microscopy, bending and hardness tests are carried out to observe wood/polymer
composite stability. First results suggest that high moisture content in wood increase pre-polymer
penetration.
Due to the polymer inlaid in wood cells, the green-glued material is expected to be more durable than
dried-glued wood. Progress of this study will be focused on the effect of swelling/shrinkage stability for
durability of coating or stability of this material during thermal treatment.
References
[1]
Pommier, Compréhension de l’aboutage du bois vert : détermination du procédé et principes
physico mécaniques appliqués au Pin maritime, 2006.
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138
Cost-Workshop
Overheating process dynamics of chipboard with addition of waste chips
Agnieszka Kurowska1, Piotr Borysiuk1, Marcin Zbieć1
1
Warsaw University of Life Sciences – SGGW,
Faculty of Wood Technology,
ul. Nowoursynowska 159,
02-776 Warsaw,
Poland
[email protected]
[email protected]
[email protected]
Key words: overheating time, pressing time, waste chips, chipboards, plywood industry
Abstract
Wood industry during last years copes with lack of wood material. Because of that for chipboard
production waste wood is being used (pieces, sawdust, recycled wood). Tests performed in Division of
Composite Wood Products of Warsaw University of Life Sciences in Warsaw show that waste chips
differ significantly from technological chips, dimension wise, shape wise and by bulk density. Therefore,
it is necessary to test pressing regime of chipboard containing waste material [3,4].
Overheating time plays significant role in overall pressing performance. It should be short enough to
provide reasonable productivity but long enough to harden the glue, which is necessary for retrieval of
pressing load without bond defects. It is assumed that overheating time depends mainly on water in the
load, which means total water content of chips and glue [1,2,5].
Following work presents influence of waste chips addition on chipboard overheating time. Waste chips
were obtained by shredding of waste coming from edging of interior and waterproof plywood. Three
layer chipboard of 16 mm thickness and 650 kg/m3 density were produced, outer layer to inner ratio was
50%. Reference boards and boards containing 20, 40, 60, 80 i 100% of waste chips in the inner layer
were produced. An melamine-urea-phenol-formaldehyde adhesive (external layers: MUPF – 50 p.b.w.,
hardener – 3 p.b.w., water – 12 p.b.w., internal layer: MUPF – 50 p.b.w., hardener – 7 p.b.w., water – 8
p.b.w.) was used for bonding. Glue content of outer and inner layer reached 12 and 10% respectively.
Boards were pressed at 180°C in 3 MPa by 5 minutes.
Figure 1: Overheating process regime of 16mm chipboard of 650 kg/m3 density in dependence on waste chips content
in the inner layer.
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It was concluded that three-layer chipboard with addition of waste chips has shorter overheating time up
to 100oC measured in the middle of the board. No significant difference between interior and waterproof
plywood chips filling on overheating time was found. Bulk density of industrial and waste chips equals
183 and 275 kg/m3, respectively. Addition of waste chips of greater bulk density causes load thinning.
For reference and 100% waste chips in inner layer boards, load thickness equals 63 and 53 mm,
respectively. Lower load thickness lowers distance between press plates, which results in lower distance
from the plate to the middle of the manufactured board. Therefore quicker temperature increase occurs in
the boards with waste chips, causing significant production performance increase.
Acknowledgement: Presented problematic of applicability of waste plywood for chipboard production
is part of the research performed for PhD thesis on Faculty of Wood Technology of Warsaw University
of Life Sciences.
References
[1]
[2]
[3]
[4]
[5]
140
Dziurka, D., Mirski, R., Łęcka, J., (2006), The effect of pine particle moisture content on
properties of particleboards resinated with PMDI, Electronic Journal of Polish Agricultural
Universities 9(1), #16.
Hata, T., Subiyanto, B., S. Kawai, S., Sasaki H., (1989), Production of particleboard with
steam-injection, Wood Science and Technology 23(4) : 361-369.
Kozakiewicz, P., Nicewicz, D., (2003), Surowce włókniste i sposoby ich rozdrabniania,
SGGW Warsaw.
Lykidis, Ch., Grigoriou, A., (2008), Hydrothermal recycling of waste and performance of the
recycled wooden particleboards, Waste Management 28 : 57-63.
Palardy, R. D., Haataja, B. A., Shaler, S. M., Williams, A. D., Laufenberg, T. L., (1989),
Pressing of wood composite panels at moderate temperature and high moisture
content, For. Prod. J. 39(4) : 27-32.
Cost-Workshop
Possibilities and limitations of advanced radiation methods for imaging of
wood
David Mannes1, Eberhard Lehmann1
1
Neutron Imaging and Activation Group
Paul Scherrer Institut
CH-5232 Villigen PSI
[email protected]
[email protected]
Key words: X-ray imaging, neutron imaging, structure, density, moisture content
Abstract
Transmission measurement of radiation, be it electromagnetic waves such as X-ray or particles such as
neutrons, can be used to non-destructively investigate the inner structure and composition of an object.
While radiation can in principle penetrate matter, only a part of it is transmitted and passes the object
without interaction, while another part of the radiation interacts with the atoms inside the object. To
which extent the radiation interacts with the object depends on one hand of the radiation (type, energy)
and on the other hand on the material (elemental composition, density). The attenuation of radiation
follows in a first order approach Lambert-Beer’s-law :
I = I0 ⋅ e −Σ ⋅z
(1)
where I is the intensity of the incident beam, I0 the intensity of the transmitted beam, Σ is the attenuation
coefficient and z the thickness of the object/sample. The attenuation coefficient Σ, or µ in the case of Xray, is the main parameter describing to which extent radiation is attenuated by a material and it is highly
depending on the type of radiation a sample is exposed and on its energy. X-radiation has a strong
correlation with the atomic number, thus elements with a higher atomic number have a higher probability
to interact with this radiation, the attenuation coefficient is therefore increasing. Neutrons do not show
such a strict correlation. Here, some light elements such as hydrogen or boron show high interaction
probabilities (and attenuation coefficients) while some heavy elements such as lead are practically
transparent [1].
These differences in the interaction behaviour of neutrons and X-ray with matter result in different
sensitivities for the elements of the periodic table. Wood, consisting mainly of the elements carbon,
oxygen and hydrogen, has a relatively low attenuation coefficient for X-ray but due to its hydrogencontent a relatively high attenuation coefficient for neutrons. This results in different areas of application
for the different types of radiation.
X-ray based testing methods include a large variety of possible investigations at different scales: at
microscopic scale using synchrotron radiation or micro- or even nano-spot X-ray tubes allow for
investigations with a spatial resolution around or even below 1 µm; the macroscopic scale is available
with industrial CT-scanners allowing the assesment of large scale objects (several dm’s).
Neutron imaging yields due to its high attenuation coefficient a relatively good contrast; the method is
however limited with concern of the spatial resolution. Here, a resolution of 30 µm is available
(theoretically limited to 10 µm); this limitation is mainly due to the fact that neutrons can not be detected
directly, the detection has to fall back on indirect detection. The high attenuation coefficient of wood is
also limiting the size of the samples, which can be examined with this method to small and medium sized
samples with a thickness in beam direction to few centimetres. The high sensitivity for hydrogen results
in a considerably higher sensitivity for water compared to X-ray which allows for accurate qualitative
and quantitative investigations of moisture contents and moisture transport processes in wood [2].
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Within the scope of this work the possibilities and limitations of imaging with neutrons, X-ray and
synchrotron light will be presented on the basis of examples. The experiments serving as examples were
all carried out at the research facilities of the Paul Scherrer Institute (PSI) in Villigen (CH). Here, a
synchrotron (SLS) as well as a neutron source (SINQ) with beamlines dedicated for imaging (TOMCAT
@ SLS; NEUTRA & ICON @ SINQ) [3] are available. The neutron imaging beamline NEUTRA allows
experiments with thermal neutrons and also investigations with X-ray. Due to an identical experimental
geometry direct referencing/combining of neutron and X-ray data is possible.
References
[1]
[2]
[3]
142
Mannes, D., Josic, L., Lehmann, E., Niemz, P. (2009) Neutron attenuation coefficients for noninvasive quantification of wood properties. Holzforschung 63(4):472-478.
Mannes, D., Sonderegger, W., Hering, S., Lehmann, E., Niemz, P. (2009) Non-destructive
determination and quantification of diffusion processes in wood by means of neutron imaging.
Holzforschung 63: 589–596.
Mannes, D. Non-destructive testing of wood by means of neutron imaging in comparison with
similar methods. PhD thesis. ETH Zurich.
Cost-Workshop
Contact free measurement of complex shapes in the wood industry
Lars Blomqvist1, Jimmy Johansson1, Dick Sandberg1
1
Linnæus University
351 95 Växjö
SWEDEN
[email protected]
Key words: Optical scanning, bended laminated veneer products, 3D- coordinate measurement
Abstract (Times New Roman, bold, 10 pt, center)
There is an increasing need to update and correct information about product geometry in the wood
manufacturing industry. Changes in machinery or personnel can be the cause of that need. Manual
measurement takes time and different ways of digitizing the geometry of the products have therefore
been developed. In this study, two methods have been tested together in order to determine the position
of a product in relation to the processing machine, and to optically scan the product geometry. The aim
was to identify and evaluate methods to digitize product geometry into a CAD-model for the wood
industry. The seat shell measured was fitted in the CNC-machine where the processing later would be
performed, figure 1.
Figure 1: The seat shell used in the study.
The form of a seat shell changes when it is fitted into a machine. Therefore this seat shell was measured
when fitted, since the result should be used for future processing. One of the methods, 3D-coordinate
measurement, gave the coordinates of pre-placed markers used to determine the position of the product
in relation to the machine. Measuring points were indicated by placing markers in the form of circular
stickers on the seat shell and the machine. Reference objects were placed around both seat shell and
machine. Photographs were taken from different angles and associated software distinguished the
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Cost-Action FP0904
coordinates of all the markers. The second method, optical scanning, is chosen to get surface coordinates,
i.e. a very large number of object points over the surface. Through associated software, information from
the two methods resulted in a surface model, from which contour lines then were obtained. It was
required, however, to adjust certain coordinates manually in order to avoid getting uneven contour lines.
The processing of the contour lines was based on assumptions made from the surface model.
Furthermore, some parts of the model were obscured during the scanning, which resulted in lack of
information. Therefore, the final contour model was supplemented with a surface, figure 2. From this
surface it is possible to obtain the angle needed for the contouring [1]. The two methods used have
resulted in a CAD model, figure 2, which will be the basis for future contouring of the seat shell in a
CNC-machine. The CAD model has information in the form of directing lines describing the machine’s
x-, y- and z-axis. This helps to position the model into the CAM program.
Figure 2: Processed seat shell with lines describing the machine’s x-, y- and z-axis.
Changes over time, directly into machine code, have caused the seat shells to become asymmetrical.
Therefore it was now necessary to determine the exact shape of the seat shell to obtain a perfect fit to
connecting parts. The methodology used here has made it possible to create a CAD-model from the
physical model. Based on the experience from this methodology, it would be recommended to continue
by creating of a tool that minimizes the need for after processing, i.e. the adjustment of certain
coordinates manually.
References
[1]
144
Capture 3D (2010), http://www.capture3d.com/, 2010/10/29.
Cost-Workshop
Properties of microwave heat treated wood and impregnatet
with natural oils
Stergios Adamopoulos1, Tim Beaver2, Takis Bouras3
1
Technological Educational Institute of Larissa
Department of Forestry and Management of Natural Environment
Laboratory of Forest Utilization & Wood Technology
431 00 Karditsa, GREECE
[email protected]
2
Composites & Textiles Pera
Melton Mowbray
Leicestershire
LE13 OBP, UK
[email protected]
2
ELKEDE Technology & Design Centre S.A.
12th km National Road Athinon – Lamias
144 52 Metamorphoses – Attiki, GREECE
[email protected]
Key words: microwave heat treatment, natural oils, physical properties, mechanical properties, gluing
Abstract
The poster presents selected data on physical and mechanical properties, and gluing behaviour of
microwave heat treated wood and impregnated with natural oils.
Acknowledgement: This research has been funded by the project TORCHWOOD “Development of an
affordable heat treatment process for wood”, 7th EU Framework Programme.
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146
Cost-Workshop
Improving the performance of bended laminated veneer products
Lars Blomqvist1, Jimmy Johansson1, Dick Sandberg1
1
Linnæus University
351 95 Växjö
SWEDEN
[email protected]
Key words: bended laminated veneer products, grain angle, furniture, moisture content
Abstract
Laminated bending of veneers mean that dried, thin veneers or thin wood sheets are glued together under
influence of pressure and eventually increased temperature. At the same time the product is given its
desired shape, most often curved. This thermo hydro mechanical process offers several benefits. For
example thick bends of small radiuses of any species of wood may be formed and poor quality wood
containing knots, splits and other defects may be utilised. Laminated bends can usually be set more
readily and made to conform better to the shape of the form than similar bends of solid wood. Further no
softening treatment is generally required before the pieces are bent. However, there are also
disadvantages e.g. more technical skill and better equipment are usually required than for solid wood
bending. The presence of glue may be somewhat detrimental to the machines used for the final cleaning
up of the bent pieces. Further the glue lines which are usually visible on the sides may be an aesthetical
unappreciated effect [1],[2].
The quality of the laminated bended veneer products are obtained as an interaction between the process,
the veneers and the glue [3]. In industries designing and producing these products it is of interest to
obtain better understanding of how processing- and material parameters affect the product quality. With
an improved understanding of the material and processing parameters it may be possible to increase the
efficiency of wood utilisation and promote the development of new processes and products that
manipulate the viscoelastic nature of wood. In particular the possibilities to obtain narrower radius of
curvature and better possibilities of bending in more than one plane would be advantageous.
This study has focused on the moisture content (MC) and the grain angle orientation in the veneers.
These two specific aspects were assumed to have a great influence on spring-back and distortions of the
laminated bended veneer products. Spring-back and distortions were therefore studied in separate tests
where MC and the grain angle orientation was varied separately in manufactured laminated bended wood
products. After manufacturing the products were exposed to variations in humidity and temperature
whereupon the spring-back and distortions were measured
Three tests were performed. For the first and the second test a seat shell was selected as test product,
figure 1a. To the third test another product was selected, figure 1b. This product was a small bookshelf.
The company producing this shelf had experienced large problems considering distortions of this
product. Further the product was very simple in shape with only one bend and therefore suitable for
measurements.
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Cost-Action FP0904
(a)
(b)
Figure 1. a) Describes the seat shell used for measurements in study one and two. b) Describes the bookshelf that was
used for study three.
In the first test the influence of MC of the veneers was investigated. In the second and third test the
influence of grain angle of the veneers was studied.
For the study veneers of birch and beech were selected in the production. For the first and third study
only birch veneers were used. The veneers were initially conditioned to equilibrium moisture contents
(EMC) according to setups in different test groups. For the first study a test group was also built up from
veneers taken directly out of production to study the industrial conditions. The seat shells in this test
group contained veneers conditioned to EMC 4 %, except for the surface veneers that had been stored in
the production hall. The humidity and temperature conditions in this room corresponded to MC 7 %.
The manufacturing of the products were performed in industrial conditions. In the tests the products were
built up from a number of veneers and the studied factors were varied between the veneers in a
controlled manner.
The results from the first test showed that the MC of the veneers influenced the spring-back and the
distortions. A large moisture gradient between veneers and especially unsymmetrical placements of these
in the construction were especially critical. The results from the second and third tests showed that grain
angle deviation has large effect on the distortions of the products. Even a small grain angle deviation as
in study two (5°) resulted in large problems with distortions. The study also showed that when crossing
two or more veneers with deviating grain angles there were cases when these faults interacted and
multiplied the distortions. In production grain angle deviations can be a result of inaccurate placement of
the veneers during pressing, incorrect cutting of the veneers, inherent from the growth of the tree or a
combination of these factors. Deviations of the grain angle were, however, shown to have only small
effects on spring-back.
References
[1]
[2]
[3]
148
Stevens, W.C., and Turner, N., (1948), Solid and laminated wood bending, Department of
Scientific and Industrial Research, Forest Products Research Laboratory, Great Britain.
Stevens, W.C., and Turner, N., (1970), Wood bending handbook, Woodcraft supply corp.
Woburn, Massachusetts.
Ormarsson, S., and Sandberg, D., (2007), Numerical simulation of hot-pressed veneer products
- moulding - spring-back – distortion, Wood Material Science and Engineering, 2(3/4): 130137.
Cost-Workshop
Thermo-mechanical densification (TMD) combined with an Oil-HeatTreatment (OHT) of Norway spruce in laboratory and industrial scale
C.R. Welzbacher1, C. Brischke1, E. Melcher2, K. Brandt2, A.O. Rapp1
1
Leibniz University Hannover (LUH), IBW, Herrenhäuser Str. 8, D-30827 Hannover, Germany
[email protected]
[email protected]
[email protected]
2
Johann Heinrich von Thunen-Institute (vTI), Institute of Wood Technology and Wood Biology,
Leuschnerstr. 91d, D-21031 Hamburg, Germany
[email protected]
[email protected]
Key words: Compression-set recovery, densification, field test, heat-treatment, laboratory test, swelling,
spring-back
Abstract
Heat-treatments of timber to improve specific wood properties, e.g. durability and dimensional stability,
are meanwhile well established industrial processes in Europe. However, the main drawbacks of heat
treated timber are reduced strength and hardness. Consequently, a thermo-mechanical densification
process (TMD) was applied to untreated Norway spruce (Picea abies Karst.) to increase its initial
strength substantially prior the application of an oil-heat treatment process (OHT). The TMD in
laboratory scale was carried out in a temperature range from 140°C to 200°C for durations from 0.5h to
4h followed by a laboratory OHT-process at 180°C, 200°C, and 220°C for 2 and 4h. Mechanical
strength, swelling properties and biological properties were investigated on matched samples to identify
suitable combinations of TMD and OHT for use in loaded outdoor applications. Further on, the process
parameters assessed from laboratory scale were taken over for industrial scale production. The results
showed that compression-set recovery of laboratory and industrial TMD-OHT spruce was almost
completely eliminated by an OHT at temperatures above 200°C, as demonstrated in laboratory tests and
also after 72 months of natural weathering. However, the strength properties of TMD-OHT spruce from
industrial scale production fell short from the material quality expected from the results of the laboratory
trials. This was attributed to the impact of the non-optimized commercial OHT process. Thus, with
regard to the improved dimensional stability and durability, industrially produced TMD-OHT appears to
be suitable for non-loaded weathered applications out of ground contact. Nevertheless, if load bearing
applications of TMD-OHT are aspired, the up-scaling of the OHT-process must consider the specific
properties of densified timber to achieve a durable and stable material of high strength, as it was
achieved by the combination of adapted and sensitively controlled laboratory scale processes.
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150
Cost-Workshop
Enhancing the quality of high pressure steamed Robinia wood at
industrial scale
Róbert Németh1, László Tolvaj2, Sándor Molnár3
1
University of West Hungary, Institute of Wood Science, Bajcsy-Zs. U. 4., H-Sopron 9400, Hungary
[email protected]
2
3
University of West Hungary, Institute of Physics, Bajcsy-Zs. U. 4., H-Sopron 9400, Hungary
[email protected]
University of West Hungary, Institute of Wood Science, Bajcsy-Zs. U. 4., H-Sopron 9400, Hungary
[email protected]
Key words: steaming, Robinia wood, high pressure, internal stresses, case hardening
Abstract
Robinia wood is a highly appreciated material for different applications, especially for outdoor
conditions because of its outstanding biological durability and high mechanical stabiulity. The demand
on the wood market for dark materials is still a well noticeable trend. However the utilization of dark
tropical species is under heavy discussion, nevertheless because of the questionable sustainability of the
raw material supply.
Recognizing these developments some European companies started to produce dark steamed Robinia in
order to substitute dark tropical species for products like parquets and furniture. During the last decades
numerous scientific investigations and industrial tests were performed in order to create reliable
schedules for steaming of Robinia wood. Those investigations were mainly focusing on steaming at
atmospheric pressure and below 100°C. Under these conditions the really dark colours could not be
reached, or only during very time-consuming treatments, which are unrealistic for industrial applications.
The long treatment times at atmospheric pressure can be reduced effectively by using temperatures above
100°C in saturated steam atmosphere. The treatment above 100°C takes only days instead of weeks
compared to normal temperatures and pressure. Beside the desired dark colour other quality aspects like
internal stresses, cracks, deformations, colour homogeneity are very important factors for the yield and
value of the final product. Compared to softwoods, the high density of Robinia wood, the extremely low
permeability, and the high extractive content forecast a special behaviour during and after the treatment,
as numerous industrial experiences and sometimes claims prove this.
An industrial autoclave of a volume of 125m3 was investigated in this research work. The main target
was to minimize the number and size of cracks, to reach homogen colour, and to minimize the internal
stresses. Different influencing factors were defined like: steaming temperature, drying before or after the
steaming, cooling of the chamber, and dimension of the treated wood material.
5 different schedules (treatment combinations) were defined and tested. After the treatments the final
moisture content, the case hardening (internal stresses), the colour homogeneity, the number, size and
location of cracks were recorded and evaluated.
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152
Cost-Workshop
Simultaneous shaping and fixation of veneer by specific material
modification
Nadine Herold, Alexander Pfriem
Eberswalde University for Sustainable Development - University of Applied Sciences
Alfred-Möller-Straße 1
16225 Eberswalde, Germany
[email protected]
[email protected]
Key words: thermo-chemical modification, form fixation, forming, furfuryl alcohol, veneer
Abstract
The aim of a project at the Eberswalde University for Sustainable Development is to develop a process to
combine shaping and fixation of veneer by a wood modification procedure. The forming process occurs
near-net-shape, i. e. there are no fundamental following process steps necessary concerning the forming.
This procedure occurs by a combined process, where the process steps plasticization, shaping and
fixation of the shape occurs in one operation, e. g. in a heating press.
For this purpose the wood is impregnated with a two component solution consisting of furfuryl alcohol
and anhydrites of carbon acids. It undertakes the tasks of plasticization as well as the fixation of the
shape after the densification and shaping process. The fixation of the shape is reached as result of a
temperature induced acid catalytic polymerisation of furfuryl alcohol. Thereby covalent bonds to the
wood substance are linked [1].
By shaping tests based on the cupping test according to Erichsen (DIN EN ISO 20482 [2] - this test
method for testing veneer is described in detail by Wagenführ et al. (2006) [3]) could be demonstrated
that the forming path can be increased considerably by the impregnation. Fig. 1 shows Force-Forming
path-curves which describe the behavior of the modified material.
Figure 1: Impregnated vs. native Veneer by shaping based on the cupping test according Erichsen
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By investigations using a pycnometer it could be demonstrated that furfuryl alcohol penetrates the cell
walls and causes a bulking effect prior to curing. An in-situ polymerization to a furan resin could be
induced by temperature in the hot-press. The targeted level of loading and a resultant plasticization have
not yet been established and are also part of this research project.
Acknowledgement: The project this publication based on is financially supported by the German
Research Foundation (DFG, PF 686/4-1).
References
[1]
[2]
[3]
154
Nordstierna, L., Lande, S., Westin, M., Karlsson, O., and Furó, I., (2008), Towards novel
wood-based materials: Chemical bonds between lignin-like model molecules and poly(furfuryl
alcohol) studied by NMR, Holzforschung 62(6): 709-713.
DIN EN ISO 20482, (2003), Metallische Werkstoffe - Bleche und Bänder - Tiefungsversuch
nach Erichsen (ISO 20482:2003).
Wagenführ, A., Buchelt, B., and Pfriem, A., (2006), Material behaviour of veneer during
multidimensional moulding, Holz als Roh- und Werkstoff 64(2): 83-896.
Cost-Workshop
Comparative studies of sorption isotherms and swelling behaviour of heat
treatment and untreated hardwoods
Željko Gorišek 1, Aleš Straže1
1
Department of Wood Science and Technology, Biotechnical Faculty, University of Ljubljana, Slovenia
[email protected]
[email protected]
Key words: wood, heat treatment, hygroscopicity, sorption, GAB model, black locust, ash, maple, beech
Abstract
Heat treatment of wood is an effective method to reduce equilibrium moisture content and to improve its
dimensional stability. In recent time the use of high temperature treatment to alter the properties of wood
has become more and more acceptable also for hardwoods. Such treatment can be used to create a "new
material" with environmental friendly technology, without adding harmful chemicals.
At temperatures range from 160 to 260 °C the chemical structure of lumber is permanently modified and
therefore the physical and chemical properties of wood are changed [1]. In spite of reduction of some
mechanical properties [2] the improvement of dimensional stability [3], reduction of hygroscopicity [4]
and increase of bio-durability are more effective and pronounced for using it [5]. The industrial
processes of thermal heating vary due to kiln design, type and condition of the heating, and treatment
schedules.
The aim of our examination was to realise the effect of thermal treatment in industrial conditions on
some domestic hardwood species. For estimation the effect of heat treatment on wood properties we
examined:
the EMC of wood in adsorption and desorption process on seven steps in hygroscopic range;
the regression curve with fitting data with GAB sorption model.
Comparative analyze was made between industrial treated and control (untreated) samples of four
domestic hardwood species.
Before heat treatment the boards of four domestic wood species (namely: black locust (Robinia
pseudoacacia L, ash (Fraxinus excelsior L), maple (Acer pseudoplatanus L) and beech (Fagus slylvatica
L)) had been kiln-dried. Afterwards all wood samples were heat treated at the same time in an industrial
furnace. The samples were warm up in steam atmosphere and heated at temperature around 210 °C. The
treatment was finished with conditioning and cooling.
Two parallel samples were step by step equilibrated in adsorption and desorption process. The required
interval equilibration was achieved above nine saturated salt solutions in thermostatically controlled (21
± 0.1 °C) sealed containers with forced air circulation and mixing of solution. After each equilibration
mass (± 0.0001 g) and dimension (± 0.01 mm) of samples were measured for determining adequate
equilibrium moisture contents and shrinkage in radial as well as in tangential direction.
The EMC were calculated for desorption and adsorption process. The GAB models of sorption isotherms
were fitted to experimental data [6].
It was confirmed that heat treatment of wood is an effective method to reduce it equilibrium moisture
content (Fig. 1). The differences between treated and control samples were at ash and maple in all
hygroscopic range very high and constant at all examined relative humidities. At lower relative humidity
the difference of EMC between treated and control wood were for black locust and beech surprisingly
very small, with the ratio around 0,70. With increasing relative humidity the ratio dropped to 0,50. High
density of black locust and beech and nonuniform heating during process were probably the reason of
lower effect of treatment on EMC and on colour.
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Analyse of sorption characteristic showed quite good correlation with GAB model which confirmed the
lowering of wood higroscopicity after the thermal treatment. Noticeable much smaller was monolayer
capacity (u0) (Tab. 1). The “energy” constant (C) was statistically insignificant comparing treated and
untreated-control samples. Constant (K) was very inconsistent and explain greater variability of EMC at
higher relative humidity.
0,90
0,80
EMC T / EMC C
0,70
0,60
Black locust
0,50
Ash
0,40
Maple
Beech
0,30
0,20
0,10
0,00
28,1
37,1
49,6
64,9
78,3
87
96
Relative humidity RH [%]
Figure 1: The ratio of equilibrium moisture content between treated (EMC T) and control (EMC C) samples for black
locust, ash, maple and beech.
Table 2: Coefficients of GAB sorption model for treated (T) and untreated (C) species.
Wood species
Coefficients of GAB model
Coef.of det.
u0
C
K
R2
Black locust T
Black locust C
0,026
0,040
0,684
0,782
10,156
6,099
0,76
0,93
Ash T
Ash C
Maple T
Maple C
Beech T
Beech C
0,023
0,045
0,020
0,044
0,021
0,043
0,747
0,782
0,784
0,772
0,811
0,777
4,892
7,261
5,725
6,514
28,533
4,387
0,72
0,89
0,85
0,92
0,79
0,93
References
[1]
[2]
[3]
[4]
[5]
[6]
156
AKGÜL, M., GÜMÜSKAYA, E., KORKUT, S. 2007. Crystalline structure ofheat. treated Scots pine
(Pinus sylvestris L.) and Uludag fir (Abies nordmanniana (Stev.) subsp. bornmuelleriana
(Mattf.)) wood. Wood Sci TecImol, 41:281-289.
JOHANSSON, D., MOREN, T. 2006. The potential of colour measurement for strength prediction
ofthermally treated wood. Holz Roh-Werkstoff, 64:104-110.
ESTEVES, B., MARQUES, A.V., DOMINGOS, I., PEREIRA, H. 2007. Influence of stearn on the
properties of pine (Pinus pinaster) and eucalypt (Eucalyptus globulus) wood. Wood Sci
Technol, 41:193METSÄ-KORTELAINEN, S., ANTIKAINEN, T., VIITAINIEMI, P. 2006. The water absorption of
sapwood and heartwood of Scots pine and Norway spruce heat-treated at 170°C, 190°C, 210°C
and 230°C. Holz Roh-Werkst, 64(3):192197.
BOONSTRA, M.J., TJEERDSMA, B., 2006. Chemical analysis of heat treated softwoods. Holz
Roh- Werkst, 64: 204-211.
TIMMERMANN, E. O. 2003 Multilayer sorption parameters: BET or GAB values? Colloids and
Surfaces A: Physicochemical and Engineering Aspects, 220 (3): 235-260.
Cost-Workshop
Author
Index
157
Cost-Action FP0904
A
Abbasion Saeed
61
Adamopoulos Stergios
145
Allegretti Ottaviano
37
Almeida Giana
27, 47, 51, 119
Altgen Michael
17
B
Beaver Tim
Bergemann Holger
Blanchet Pierre
Blomqvist Lars
Bonarski Jan T.
Borysiuk Piotr
Botsis John
Bouras Takis
Brandt Karin
Brischke Christian
Brito José Otavio
C
Candelier Kévin
Carmeliet Jan
Castera Patrick
Chaouch Mounir
Clair Bruno
Cloutier Alain
Cuccui Ignazia
Cugnoni Joël
Czarniak Paweł
145
35, 41
93
143, 147
21
139
117
145
149
149
27
101
61
137
39, 101
73
93
37
117
109
D
Danis Michel
Derome Dominique
Dupleix Anna
137
61
115
F
Fang Chang-Hua
Fellin Marco
Ferrari Silvia
Fioravanti Marco
Froidevaux Julien
93
37
37
121
121
G
Gabbitas Brian
Gerardin Philippe
55, 87
39, 101
158
Girardet Fred
71
Gorišek Željko
155
Grigoriou Athanasios
31
Gril Joseph
73, 113, 121, 123
Grześkiewicz Marek
105, 109
H
Hahn Benjamin
131
Haller Peer
85, 95, 103
Hampel Uwe
85
Hecksher Thomas
81
Heiduschke Andreas
95
Henchoz Nicolas
71
Herold Nadine
153
Hofmann Tamás
35, 41
Holm Jens Kai
81
Huber Hermann
23
Hughes Mark
97, 115, 127, 135
J
Jamnani Behnam
Jirouš-Rajković Vlatka
Johansson Jimmy
Jones Dennis
79
25
143, 147
125
K
Kaliske Michael
Kamke Frederick A.
Kawai Shuichi
Kegel Edo
Kifetew Girma
Koubaa Ahmed
Kurowska Agnieszka
Kutnar Andreja
89
59, 65, 77
113, 123
125
67
93
105, 139
65, 77
L
Laflin Nick
Laine Kristiina
Läppanen Kirsi
Lavalette Anne
Lehmann Eberhard
Longis Lea
Lv Pin
Lykidis Charalampos
97
97
81
137
141
71
27
31
Cost-Workshop
M
Mannes David
Marchal Patrice
Marchal Rémy
Matsuo Miyuki
Melcher Eckhard
Miklečić Josip
Militz Holger
Molnár Sándor
Montero Cedric
141
47
115
113, 123
149
25
17, 49
151
73
N
Navi Parviz
Németh Róbert
Niemz Peter
Nilsson Jonaz
117, 121
151
35, 41
67
O
Olek Wiesław
Ormarsson Sigurdur
21
55, 87
P
Pearson Hamish
55, 87
Perré Patrick
27, 47, 51, 69, 119
Pervan Stjepan
25
Petrissans Anélie
39
Petrissans Mathieu
39, 101
Pfriem Alexander
99, 153
Pierre Floran
119
Plenzler Ryszard
21
Pommier Régis
137
Popescu Carmen-Mihaela
45
Popescu Maria-Cristina
45
Posselt Dorthe
81
Prekrat Silvana
25
R
Rapp Andreas O.
Rassam Ghonche
Rautkari Lauri
Rémond Romain
Rétfalvi Tamás
Rhême Martin
Rogenmoser Christian
Rossmaier G.
Ruponen Jussi
149
79
97, 127, 135
51, 69
35, 41
117
75
131
135
S
Saft Susanne
Salmén Lennart
Sandak Anna
Sandak Jakub
Sandberg Dick
Santos Diego V.B.
Schnabel Thomas
Schreiber Julia
Schwarz Ulrich
Serimaa Ritva
Sieverts Tom
Stamm B.
Straže Aleš
Sugiyama Junji
89
19
37
37
67, 143, 147
47
23
85
99
81
35, 41
131
155
113
T
Thoemen Heiko
Tolvaj László
91
151
U
Umemura Kenji
123
V
Vasile Cornelia
Volkmer Thomas
45
121
W
Wehsener Jörg
Weinand Yves
Weissensteiner Josef
Welzbacher Christian
Wetzig Melanie
Wieland Stefanie
Wilkowski Jacek
Willems Wim
Y
Yin Yafang
Yokoyama Misao
Z
Zbieć Marcin
Zürcher Ernst
103
131
59
149
35, 41
23
109
49
19
113, 123
139
75
159

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