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EFFECT OF STEAMING ON THE PERMEABILITY OF WOOD

Lu Jianxiong; Bao Fucheng; Jiang Xiaomei; Zhou Ming (Institute of Wood Industry, Chinese Academy of Forestrg Beijing 100091)  
The effect of steaming on the permeability of spruce (Picea jezoensis var. komarovii), fir (Abies nephrolepis) and pine (Pines koraiensis) woods were studied. The green and air-dried specimens (2 ×2 ×5cm) for treatment were steamed at 120℃(1kg/cm2) and 100℃ (1kg/cm2) for 8 hours under water vapor saturated conditions and then subjected to air-drying untill about 10% moisture content. A rising-water volume-displacement method was used to measure air permeability in the longitudinal direction of the wood. The gas permeabilities of the steamed specimens were compared with those of matched unsteamed controls (m. c. ≈10%). The result showed that the effect of steaming on the permeability of wood is variable due to that the change of wood structure and chemical composition caused by steaming is not the same in different wood species with different properties. The average permeability of steamed at 120℃ and 100℃ air-dried pine sapwood and heartwood was increased by approximately 60%, 90% and 40%, 130%respectively. The average permeability of steamed at 120℃ green sprucesapwood and steamed at 100℃ air-dried spruce heartwood were increased by approximately 326% and 80%. The increase in permeability of steamed wood was attributed to produce crack in pit membrane and torus after steaming.Paired comparison analyses (t) were carried out between the steamed and the matched unsteamed specimens. Significant was at the 90-99.9% level.However, steam treatment had no effect on the permeability of steamed green spruce heartwood, air-dried sapwood and heartwood, as well as steamed green fir heartwood, air-dried sapwood and heartwood.
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