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)

4

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)

0

5

10

15

20

25

30

35

40

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

20

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)

0

10

20

30

40

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)

0

5

10

15

20

25

30

35

40

45

01.

12.2

007

14.

12.2

007

27.

12.2

007

09.

01.2

008

22.

01.2

008

04.

02.2

008

17.

02.2

008

01.

03.2

008

14.

03.2

008

27.

03.2

008

09.

04.2

008

22.

04.2

008

05.

05.2

008

18.

05.2

008

31.

05.2

008

13.

06.2

008

26.

06.2

008

09.

07.2

008

22.

07.2

008

04.

08.2

008

17.

08.2

008

30.

08.2

008

12.

09.2

008

25.

09.2

008

08.

10.2

008

21.

10.2

008

03.1

1.2

008

16.1

1.2

008

29.1

1.2

008

12.

12.2

008

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)

4

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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1

5

6

7

4

1

4

8

10 °C-Isotherme

9

23

1

5

6

7

4

1

4

8

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