The Behaviors of Endothermic and Exothermic of Wood and Wood Components between 100°C and 200°C

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To clarify the mechanism of the heat-treatment for wood between 100°C and 200°C, the behaviors of endothermic and exothermic of wood and wood components (cellulose, hemicellulose, lignin) between 100°C and 200°C under the dried air condition were measured using the temperature-modulated DSC. The measurement were carried out in the heating processes under stepwise heating and cooling cycles (100°C→140°C→100°C→160°C→100°C→180°C→100°C→200°C, ±5°C/min). The total heat flow (THF) and the nonreversing heat flow (NRHF) curves of wood, cellulose and hemicellulose in the 1st heating process (100°C→140°C) were found in the exothermic side compared with the curves in other heating processes. The reversing heat flow (RHF) curves of wood in the 4th heating process (100°C→200°C) were found in the exothermic side compared with the curves in other heating processes. However the RHF curves of cellulose and hemicellulose were observed on the almost same line. The THF and NRHF curves of lignin were shifted to the exothermic side with the stepwise heating and cooling cycles. On the other hand, the RHF curves of lignin were shifted to the endothermic side with the cycles. These results suggest that the effects of the heat-treatment for wood between 100°C and 200°C are based on the thermodynamic stabilization of the conformation of cellulose, hemicellulose and especially lignin due to the heating history.