Modified Wood: Sustainable and Durable

by: Waldemar J. HomanSHR Timber Research

Sustainable Technologies for the

Production of Durable Wood

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Restrictions of Wood

• Durability (resistance against biological attack of fungi and insects)

• Shrinkage and swelling– anisotropy– unequal swelling in greater dimensions– adhesion problems with paints

• UV-degradation• Water adsorption and desorption

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“Classical” Wood Preservation

• Mechanism toxicity (f.i. heavy metals)• Disadvantages:

– emissions during production– emissions during use– emissions after use (waste stage)

• New legislation• Public image

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Alternatives to “classical” wp

• Durable tropical hardwood species– sustainable forest management– quality of plantation grown wood– availability

• Shift to other materials– pvc– steel– aluminium

• Alternative treatment methods

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Alternative treatment methods

• Lumina filling resin treatments

• Cell wall filling resin treatments

• True modification of the cell wall

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Wood structure and Distribution of the chemical components within the

woody cell wall

Cell wallCell wall

Association of Association of cellulose, polyoses and cellulose, polyoses and ligninlignin

Cell lumenCell lumen

Chemistry of the components

Cellulose– Long chains of

anhydroglucopyranose

– Native cellulose

DP 3.500 - 12.000

– Fibrils

– Crystallinity and amorphous zones

Mechanism of water uptakeSHR

Resin treatments

• Filling lumina no penetrationof cell wall

• Bulkingpenetration of cell wall cavities

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Modification of Wood

• Chemical alteration ofcell wall polymers– Substitution of

OH-groups

– Cross linking

– Degradation of polymers (undesired)

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Etherification of woodSHR

W o o d O H + C H 3 C l W o o d O C H 3 + H C l

W o o d O H + W o o d OO H

R

R '

OR R '

E t h e r i f i c a t i o n o f w o o d :

a . w i t h m e t h y l c h l o r i d eb . w i t h a n e p o x i d e

Esterification of woodSHR

W o o d O H +

O

R O H

O

OW o o d R+ H 2 O

W o o d O H +

O

R O R '

O O

OW o o d R+

O

O HR '

E s t e r i f i c a t i o n o f w o o d :

a . w i t h a c a r b o x y l i c a c i db . w i t h a n a l k y l i c a n h y d r i d e

Silanisation of woodSHR

W ood OH + W ood O S i

R

R'

R''

H XW ood O S i

R

R'

R''

X S i

R

R'

R''

+

S ilyla tion of wood with an a lkylsilane

R S i(OR)3 R S i(OH)3

R S i(OH)33 HO S i

OH

R

O S i

R

OH

O S i

R

OH

OH

HO S i

OH

R

O S i

R

OH

O S i

R

OH

OH

OH OH OH

W ood

Hydro lys is

C ondensa tion

100 °CHO S i

O

R

O S i

R

O

O S i

R

O

OH

W ood

-H2O

+ 3 + 3H2O ROH

-H2O

R eaction of wood with an a lkoxysilane (according to G oetha ls et a l., 1996)

Urethane treatmentsSHR

W o o d O H + R N C O W o o d O N

O

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R e a c t i o n o f w o o d w i t h a m o n o - i s o c y a n a t e

Resin treatments

• Non modifying– alkyds– acrylates– epoxides *– melamine

• Modifying– DMDHEU– epoxides *

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AcetylationSHR

+

H3C

H3C

O

O

O

WOOD O

CH3

O

+

OH

O

H3CWOOD OH

Sorption curves of acetylated wood

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0

5

10

15

20

25

30

0 20 40 60 80 100

humidity [%]

EM

C (

%)

Beech

WPG 10 %

WPG 18%

Soft rot resistance of acetylated wood

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-10

0

10

20

30

40

50

0 5 10 15 20

WPG (%)

We

igh

t lo

ss

[%

]

A two steps process:A two steps process:1 hydro-thermolysishydro-thermolysis 165 °C - 185 °C165 °C - 185 °C

dryingdrying conventionalconventional

2 curingcuring 170 °C - 190 °C170 °C - 190 °C

1 2

Selectively reorganizing theSelectively reorganizing thechemistry of woodchemistry of wood

Cellulose

Hemicellulose

Lignin

CCCCrrrroooo ssss ssss lllliiiinnnnkkkkiiiinnnngggg

Water resistant

structure

RRRReeee aaaacccc ttttiiiivvvveeee iiiinnnntttteeee rrrrmmmmeeee ddddiiiiaaaatttteeee ssss IIII((((eeee ....gggg .... aaaallllddddeeee hhhhyyyyddddeeee ssss ))))

RRRReeee aaaacccc ttttiiiivvvveeee iiiinnnntttteeee rrrrmmmmeeee ddddiiiiaaaatttteeee ssss IIIIIIII

Cellulose

(hydro) Thermal treatment(hydro) Thermal treatmentThe Process Principle of the “Plato process”The Process Principle of the “Plato process”

The Plato process chemically

ModifiedModifiedhydrofobichydrofobiccomplexcomplex

cellulosescelluloses

X

lignin

hemicelluloses

celluloses

acids

sugars

low-molecular-

weight fenolic units

aldehyds

+

+

X+

X

X

Desired reaction path

X unwanted reactions

Improved wood properties

• High durability (fungi, insects)

• Reduced shrinkage and swelling

• UV-stability

• Strength properties (both + and -)

• Reduced EMC

LOWER MAINTENANCE

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State of the Art 2002

• Laboratory research– reaction kinetics– mechanism of activity– ultrastructural research– adaptation of test methods

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State of the Art 2002

• Search for chemicals / processes– complexity– by products / co products– toxicity (human / eco)– price– technological feasibility

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State of the Art Europe 2002

• Commercial treatment plants:

– Thermowood (SF, > 10 production sites)– Plato (NL, constructed, restart)– NOW, Perdure (F, producing)– Acetylation plant (NL, blue print) – Other processes (NL, 3 plants in 2003)

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Future of modification

• New research networks• New networks with industry

– EU Network “wood modification”

www.woodmodification-network.org

• From technology push to market pull

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Challenges

• Up-scaling• Commercialisation:

– co-operation chemical process industry and wood industry

Production of high quality and durable wood products with wood harvested from sustainable managed forests of the moderate zones

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Challenges

• Up-scaling• Commercialisation:

– co-operation chemical process industry and wood industry

Production of high quality and durable wood products with wood harvested from sustainable managed forests of the moderate zones

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