The Effect of Heat Treatment on the Chemical Composition of Ash Wood

Abstract

Common ash (Fraxinus excelsior L.) wood was heat treated in an oven at temperatures of 160, 180, and 200 oC, and under atmospheric pressure in the presence of air for a duration of 3, 6, 9, and 12 h. The impact of heat treatment on the chemical composition of wood was studied. The extractives content initially increased up to 200 oC and 3 h. However, with extended treatment duration it decreased. Hemicellulosic monosaccharide (D-xylose) degraded under all treatment conditions and resulted in a decrease of holocellulose content. In the case of lignin, demethoxylation and the formation of more condensed structures were observed. This led to an increase in lignin content at temperatures of 180 and 200 oC. The oxidation process already began at 160 °C. This resulted in the formation of new carbonyl or carboxyl groups that contributed to color change, i.e., wood darkening. From the beginning the increase in the cellulose crystallinity was observed, and then it decreased. The maximum was reached at the temperatures of 160, and 180 °C for 9 h of treatment and at the temperature of 200 °C for 6 h.