Surface Modification versus Bulk Wood Modification – Properties...
Transcript of Surface Modification versus Bulk Wood Modification – Properties...
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1st Workshop COST Action FP 1006 “Bringing new functions to wood through surface modification”
Holger Militz
Wood Biology and Wood Products
Georg-August-University Göttingen
Germany
Surface Modification versus Bulk Wood Modification –
Properties and Challenges
Content of presentation
• Why and how (principles)
• Status quo industrial applications
• Bulk treatment versus surface treatment
• Challenges and limitations
Wood modification
Photos: BASF, Titanwood
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Wood: material of the future
• Ecological
• Sustainable
• Renewable
• Esthetical
• Energy efficient
• End-of-life: energy
• Traditional and modern
Wood, not just perfect…
Maintenance problems of wood due to:
•Moisture sensitive
•UV-stability
•Dimensional movements
•Resistance against fungi
•Soft surface
Photos: Grosser, Evans, Militz
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What is wood modification?E
inle
itung
Illustration: Wepner
History of wood modification
• 1930´s: Acetylation etc. (Stamm et al., USA)
• 1970´s: heat treatment production plant FWD (Giebeler et al., D)
• 1990´s:
– Heat treatment processes (TMT)• Plato
• Thermowood
• French processes
– Acetylation with acetic anhydride• R. Simonson (Chalmers, SE)
• H. Militz (SHR, NL)
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0
50
100
150
200
250
0 12 24 36
t(h)
T(C)
Phase 1 Phase 2 Phase 3
ThermoWood ® process
Thermo treatment (TMT, Thermowood)
Photos: Plato process
- no chemicals
- temperature 180°C to 220°C
- many wood species used
- difference between producers:
-technology used
Modification technology based on liquids
• Belmadur® Technology
– (DMDHEU)
• Kebony® Technology
– (Furfurylation)
• Accoya® Titanwood
– (Acetylation)
• Silanes/ Silicones
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Kebony® production
Autoclave: 13 m length, 3.25 m diameter (0.1 - 13 bar)
Production plant, Arnhem, NL
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Use class 1-2 (EN 335)(Photos by Mitteramskogler/ Austria)
Use class 3 (EN 335) (Photos by Thermowood Association, Finland)
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Use class 3 (EN 335) (Photos by Mitteramskogler/ Austria)
Kebony® Products
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Accoya® products
Wood modification in research phase
• Silicones/ siloxanes
• Aldehydes
• Phenols
• Anhydrides
• Others…
– See several presentations during conference
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Color?
Reduced equilibrium moisture content
Improved durabilityagainst decay
Thermal conductivity?
Improved stability
Resinremoved
Strength properties?
UV stability?
Wood properties gained with modification treatment
Surface modification
Challenges and limitations
- material properties
- applications
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Color? Just on surface
Reduced equilibrium moisture content
Improved durabilityagainst decay?
Thermal conductivity: no effect
Improved stability?
Resinremoved: no effect/ limited
Strength properties? limited...
UV stability?
Wood properties gained with surface modification
Sorption properties changed (Tjeerdsma, Boonstra 1990´́́́s)
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0 10 20 30 40 50 60 70 80 90 100
Relative Humidity (%)
Equ
ilibr
ium
Moi
stur
e C
onte
nt (
%)
Heat-treated adsorption
Heat-treated desorption
Non-treated adsorption
Non-treated desorption
Scotch pine
Non-treated
Heat-treated
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0
5
10
15
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Teak Oak Meranti Beech Pine
Belmadur® Wood
Swelling/ Shrinkage [%]
Swelling/ shrinkage
Swelling/ shrinkage: improvement of surface?
• Any effect of a solid/ building part because of thin layer?
• Possible effect on performance of a coating or adhesive?
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Water repellency (Weigenand 2004)
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0 2 4 6 8
ASE 8730
ASE 8730
ASE 8730
ASE 8130
ASE 8130
ASE 8130
Control
Time (h)
Wat
er u
ptak
e (%
)
Degussa
Moisture content variation in field tests
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Moisture content in field tests (pine)
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Ho
lzfe
uch
te [
%]
unbehandelt DMDHEU Siloxane Wasserglas
Moisture content in field trials (PhD A. Gellerich)
treatment m.c. above >30%
[days]
pine beech
Untreated 52 95
DMDHEU 5 3
Siloxan 0 2
Waterglas 10 7
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*1: very few cracks; 2: few cracks; 3: moderate cracking;
4: considerable cracking; 5: many cracks
Treatment
Water-borne / acrylic Oil-based
Roughness (Ra) [µm]
Waviness [µm]
Crack level*
Roughness (Ra) [µm]
Waviness [µm]
Crack level*
Untreated 6.0 (0.8)164.8 (15.3)
4 5.5 (1.7)126.5 (10.1)
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Treated 1.0 (0.0) 17.5 (2.6) 1 1.3 (0.5) 17. 7 (6.4) 2
Surface roughness and waviness(Xie et al. 2008)
Water related properties
• Reduced liquid (water) uptake
– Positive effect on end product
– Negative effect on raw/ semi-product
• Glueability?
• Paintability? (Tingaut et al., 2005)
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Resistance against degrading fungi (brown rot, white rot, soft rot) in EN 113, Env 807, EN 252
0%
5%
10%
15%
20%
25%
30%
35%
40%
0% 5% 10% 15% 20%
weight gain after reaction
mas
s lo
ss
Interlace Treatment "A"
Interlace Treatment "B"
Interlace Treatment "C"
Coriolus versicolor, Beech
Silicones
Si O
CH3
A
CH3
Si O
R
CH3
Si O
CH3
CH3
Si
CH3
CH3
A
nm
Polydimethylsiloxane
SMA
SMI
Ø <2nm
Y
OSi
OSi
OSi
OSi
OSi
X
N
RCH3CH3
X
N CH3CH3
RY
Silicone Quats Functional groups:
CH3 / OCH3
(CH2)3 NH2
(CH2)3 NH (CH2)2 NH2
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Growth reducing activity (Ghosh et al. 2004)C
on
iop
ho
ra p
ute
ana Tram
etes versicolo
r0.05, 0.1,
0.2, 0.4, 1% QSMiE with control after
7 days
0.05, 0.1, 0.2, 0.4, 1% ASMaE with control after
7 days
0.05, 0.1, 0.2, 0.4, 1% AmSMaE
with control after 7 days
Type of fungi in field test with Pine (Gellerich 2009)
fungi Untreated Siloxan Waterglas DMDHEU
Trichoderma sp. x x x x
Epicoccum sp. x x x x
Aureobasidium
pullulans
x x
Lewia sp. x
Chaetomium sp. x
Fusarium sp. x x
- x
- x
- x
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Outside weathering of uncoated wood (Xie et al. 2008)
Effect of UV-degradation/ weathering of surfaces(photos by P. Evans)
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Change in Klason-Lignin content due to weathering of spruce veneers(by P. Evans)
Lignin degradation
1800 1600 1400 1200
1700 1505
50% DMDHEU
Wavenumber [cm -1]
1800 1600 1400 1200
1732 1505
72 h
96 h
120 h
144 h
3 h
6 h
24 h
48 h
0 h
Untreated
Rel
. Abs
orpt
ion
Wavenumber [cm -1]
FTIR Infrared-Spectroscopy (Xie et al 2005)
absorption at 1505 cm -1 representative for lignin
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Effect of DMDHEU on performance outside (22 months) (Xie et al. 2008)
8/02 11/02 3/03 5/03 9/03 12/03 3/04 6/04
30%
DM
DH
EU
untr
eate
d
Micro veneers after weathering(Xie et al. 2005)
• After 144 h artificial weathering (QUV)
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SEM (cross cut) of weathered veneers (Xie et al. 2005)
AA CB
IHG
D E F
0h 48h 144h
Untreated
10% DMDHEU
50% DMDHEU
Before QUV
SEM (radial) of weathered veneers (Xie et al. 2005)
A B C
D E F
After QUV After QUV
Untreated
30% DMDHEU
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treatment curing modifiedwood
Room temperature
wood
Temperature > 100 - 140°C
Solution
Process of bulk wood modification
Photos: BASF
Processes of surface modification
• Easier than bulk because thin layers only…but…
• Application?– Batch?
– Run through?
– Atmospheric pressure/ vacuum/ over pressure?
• Reaction conditions?– Reaction speed?
– Temperature?
– Catalysts?
– Other conditions? (N, UV-curing? Plasma?)
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Plasma treatment of wood
Patent-Nr. DE 199 57 775.7, Patent-Nr. EP 1233 854, Patent-Nr. US 10/ 148,505, Patent-Nr. J 2001-541662, Patent-Nr. Ca 2,393,952
Improved wetting and spreading
untreated Plasma treated
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X-ray-Photoelectron-Spectroscopy(XPS)
Wolkenhauer, A., Meiners, A., Rehn, P., Avramidis, G., Leck, M., Viöl, W. (2005) Haftverbesserung von Holzbeschichtungen durch Plasma-Vorbehandlung. Holztechnologie 46: 40-47
untreated plasma treated
Creation of electronegative groups
Wolkenhauer, A., Militz, H., Viöl, W. (2008) Increased PVA-glue adhesion on particle board and fibre board by plasmatreatment. Holz als Roh- und Werkstoff 66: 143-145
Improvement of adhesion
Testing of adhesion forces with peel-of test
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Wolkenhauer, A., Militz, H., Viöl, W. (2008) Increased PVA-glue adhesion on particle board and fibre board by plasmatreatment. Holz als Roh- und Werkstoff 66: 143-145
Improvement of adhesion
untreated plasma treated
WPC and wood composites: improved surfaceadhesion of glues and paints
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Processes of surface modification
• Easier than bulk because thin layers only…but…
• Penetration depth/ treated zone is just some nm-mm!!
• How to handle raw/ sawn/ semi-planed surfaces?
• How to treat complex shapes?
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10 °C-Isotherme
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10 °C-Isotherme
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Future research
• Basic research on chemicals/ processes to improve wood surfaces
- UV-stability
- water related properties
- hardness/ scratch resistance
- dimensional stability
- biological resistance
• Applied research and process development
• Include researchers from wood modification/ chemistry/ wood coatings research
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Good forum for discussion: COST FP 1006 !
Any questions?
For photos/ information thanks to:
-Carsten Mai -Yanjun Xie-Susanne Bollmus -Antje Gellerich -Phil Evans-Wolfgang Viöl