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Dimensional stabilization of wood
This document discusses various methods for stabilizing the dimensions of wood, including thermal modification, acetylation, impregnation, and compression. Thermal modification processes like Plato and Staypak heat wood to temperatures of 160-190°C to reduce hygroscopicity and increase hardness. Acetylation increases the wood's natural acetyl content through impregnation with acetic anhydride and heat treatment. Impregnation and compression methods soak wood in thermosetting resins then cure it with or without compression to stabilize dimensions, increase strength, and reduce cracking. Comparison charts show the degree of dimensional stability achieved by different wood treatment methods.
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Dimensional stabilization of wood
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- 2. Problems of Wood •Hygroscopicity • Dimensional instability • Durability • Mechano-sorptive properties 2
- 3. How to solvethese problems? • Use wood with high natural quality • Availability • Sustainability • Use of wood preservatives • Use of new technologies for wood treatment!! 3
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- 5. Thermal modification The Platoprocess • Hydro thermal treatment / hydro thermolysis (160- 190ºC 6-8 bar) • Drying (10% MC) • Curing (heating of the altered wood) (160-190ºC) 5
- 6. Thermal modification Protected againstburning using steam as an inert gas Staypak 1.25 to 1.40 g/cc 10 to 18 times hardness 6
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- 8. Acetylation • Impregnation withacetic anhydride • Reaction at elevated temperatures • Post treatment (acetic acid) Increases naturally occurring acetyl content of wood (from 1-3% to 20%) 8
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- 10. • Wood(Veneer) treatedwith 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 10
- 11. • 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 11 Impregnation Process
- 12. Impreg has anumber of properties differing from those of normal wood and ordinary plywood 12 Properties of Impregnated Wood
- 13. Similar to impregexcept that it is compressed before the resin is cured within the wood. The resin-forming chemicals (usually phenol formaldehyde) act as plasticizers 13 Compreg
- 14. • 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 14 Compreg: Process
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- 16. Very high pressingpressure 50 to 80 MPa 1MPa Pressing Pressure (PF Resin) 1.16gm/cc MOE: 29GPa MOR: 307MPa NaOH 0.5% Aqueous NaClO2 2% Aqueous 16 High strength resin impregnated compressed wood
- 17. 17 Comparison of woodtreatments and the degree of dimensional stability achieved. Comparison of wood treatments Reduction in swelling (R) or Antishrink efficiency (ASE)
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