"Hygroscopicity of heat-treated wood, 2: Reversible and irreversible reductions in the hygroscopicity of wood due to heating."
2002
"Obataya, E. (Tsukuba Univ., Ibaraki (Japan)) | Tomita, B. "
"Spruce wood specimens were heated at 60-200 deg C for 2-48hours in the absence of moisture, and their equilibrium moisture content (M) was measured. The M of wood at 57% relative humidity (RH) was reduced by heating at 100 deg C or above, but it was largely recovered after moistening at 97% RH. Similar changes were observed regardless of wood species, and were also recognized in holocellulose, alpha -cellulose and milled wood lignin. The temporary reduction in M due to heating was interpreted as the effect of annealing of the amorphous molecules in the wood cell wall, and the recovery of M due to moistening was explained by the rapid rearrangement of amorphous molecules being mobilized at high RH. By heating above 140 deg C, the M of wood was reduced irreversibly. This effect was more remarkable at higher RH. The irreversible reduction in M of wood decreased clearly with the removal of lignin, but not with the removal of hemicelluloses. In addition, the irreversible reduction in M of milled wood lignin was evidently larger than that of wood and other wood constituents. It was suggested that chemical changes in the lignin were responsible for the irreversible reduction in the M of wood due to relatively mild heating."
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