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Dimensional stabilization of wood
- 2. Problems of Wood • Hygroscopicity • Dimensional instability • Durability • Mechano-sorptive properties
- 3. How to solve these problems? Use wood with high natural quality • Availability (mid term, long term) • Sustainability Use of wood preservatives Use of new technologies for wood treatment!!
- 5. Thermal modification The Plato process • Hydro thermal treatment / hydro thermolysis (160- 190ºC 6-8 bar) • Drying (10% MC) • Curing (heating of the altered wood) (160-190ºC)
- 6. Thermal modification Protected against burning using steam as an inert gas Staypak 1.25 to 1.40 g/cc 10 to 18 times hardness
- 8. 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%)
- 9. Acetylation
- 10. 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
- 11. PROCESS • 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
- 12. Properties of Impregnated Wood Impreg has a number of properties differing from those of normal wood and ordinary plywood NB: Comparative properties will be shown later
- 13. COMPREG 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
- 14. PROCESS • 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
- 15. Properties of Compreg Wood NB: Comparative properties will be shown later
- 16. High strength resin impregnated compressed wood Very high pressing pressure 50 to 80 MPa 1MPa Pressing Pressure (PF Resin) 1.16gm/cc MOE: 29GPa MOR: 307MPa NaOH 0.5% Aqueous NaClO2 2% Aqueous
- 17. Comparative properties of modified woods Property Impreg Compreg Staypak Specific gravity 15% to 20% greater than normal wood Usually 1.0 to 1.4 1.25 to 1.40 Equilibrium swelling and shrinking 1/4 to 1/3 that of normal wood 1/4 to 1/3 that of normal wood Same as normal wood but slower Springback None Very small when properly made Moderate when properly made Face checking Practically eliminated Practically eliminated About the same Decay and termite resistance Better than normal wood Better than normal wood Normal but occurs slowly Compressive strength Increased Increased Increased Tensile strength Decreased significantly Increased less than proportional to specific gravity increase Increased about in proportion to specific gravity increase Hardness Increased 10 to 20 times that of normal wood 10 to 18 times that of normal wood Toughness About 1/2 of value for normal wood 1/2 to 3/4 of value for normal wood Same to somewhat greater than normal