Dimensional stabilization of wood

Dimensional Stabilization of Wood

Problems of Wood• Hygroscopicity• Dimensional instability• Durability• Mechano-sorptive properties

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How to solve these problems?• Use wood with high natural quality

• Availability • Sustainability

• Use of wood preservatives• Use of new technologies for wood treatment!!

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Modification methods

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Thermal modificationThe Plato process

• Hydro thermal treatment / hydro thermolysis (160-190ºC 6-8 bar)

• Drying (10% MC)• Curing (heating of the altered wood) (160-190ºC)

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Thermal modificationDrying

6-10% MCHigh Temp.180-230 ̊C

Heating2-3Hours

Hotpressing6-10 MPa

Staypak

Protected against burningusing steam as an inert gas

Staypak

1.25 to 1.40 g/cc10 to 18 times hardness 6

Chemical modification

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Acetylation

• Impregnation with acetic anhydride• Reaction at elevated temperatures• Post treatment (acetic acid)

Increases naturally occurring acetyl content of wood(from 1-3% to 20%)

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Acetylation (cont’d)

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• Wood(Veneer) treated with a thermosetting, fiber-penetrating resin and cured without compression is known as impreg.

• Stabilizes dimensions, increases strength and resistance to water, moisture, and chemicals, and reduces cracking.

Impreg

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• Green Wood• Dry Wood• 25-35%

Weight Gain

Soaking

• 1-2 Days• For Uniform

Distribution of the Resin

Nondrying condition • Drying

(Moderate Temp)• Curing

(Higher Temp)Drying and

Curing

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Impregnation Process

Impreg has a number of properties differing from those of normal wood and ordinary plywood

15% to 20% greater Specific Gravity

1/4 to 1/3 Shrinkage/Swelling

1/10 Permeability to water vapor

Better Decay, Termite, Acid Resistance

Greatly increased heat resistance

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Properties of Impregnated Wood

Similar to impreg except that it is compressed before the resin is cured within the wood.

The resin-forming chemicals (usually phenol formaldehyde) act as plasticizers

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Compreg

• Green Wood• Dry Wood• 25-35%

Weight Gain

Soaking

• 1-2 Days• For Uniform

Distribution of the Resin

Nondrying condition • Drying

(Moderate Temp)• Curing

(Higher Temp)Drying and

Curing

7-10 Mpa

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Compreg: Process

Natural lustrous finish

Sp. Gravity usually 1.0 - 1.4

1/4 to 1/3 Shrinkage/Swelling

Permeability to water vapor: much less than impreg

Better Decay, Termite, Acid Resistance

Greatly increased heat resistance

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Properties of Compreg Wood

Very high pressing pressure50 to 80 MPa

1MPa Pressing Pressure (PF Resin)1.16gm/cc MOE: 29GPa MOR: 307MPa

NaOH

0.5% AqueousNaClO2

2% Aqueous

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High strength resin impregnated compressed wood

17Comparison of wood treatments and the degree of dimensional stability achieved.

Comparison of wood treatments

Reduction in swelling (R) or Antishrink efficiency (ASE)

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