Post on 22-Mar-2017
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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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