"Hygroscopicity of heat-treated wood, 3: Effect of steaming on the hygroscopicity of wood."
2002
"Obataya, E. (Universite Montpellier II (France)) | Higashihara, T. | Tomita, B. "
"Spruce wood specimens were steamed at 120-180degC and their equilibrium moisture content (M) was compared with that of wood heated in the absence of moisture. Steaming gave larger losses in weight of wood (WL) than dry heating at the same temperature and duration. At low relative humidity (RH) (less than 57%), no reversible effect was recognized in the M of steamed wood while the M of wood heated dry recovered considerably after moistening. At 97% RH, the M of steamed wood was higher than that of wood heated dry at the same WL. The higher M value of the steamed wood was attributed to the hygroscopic nature of depolymerized hemicelluloses remaining in the wood. However, the M of the steamed wood was still higher than that of the wood heated dry, even after the removal of hygroscopic water-soluble substances. The water sorption isotherms of unheated and heated wood were analyzed by using the Hailwood-Horrobin adsorption equation. At the same WL, steaming and dry heating had the same effect on the reduction of hydrated water. On the other hand, steaming showed less effect on the reduction of dissolved water than dry heating. In addition, the amount of dissolved water increased by steaming to a 5% WL. It was speculated that steaming loosened the binding structure of the wood cell wall to increase the dissolved water, whereas dry heating tightened the cell wall structure to restrict moisture sorption and swelling of the cell wall components."
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