Chemical Changes in Wood due to Thermal Modification

There have been many studies that have attempted to elucidate the chemistry of thermolysis of wood by examining the thermal behaviour of isolated wood components, and much of the early work in this respect has been reviewed (Beall and Eickner, 1970). The use of thermal analysis techniques has shown that the results obtained are quite variable and 

Hardwoods are less thermally stable than softwoods and this is attributable to differences in the hemicellulosic content and composition. Pentosans (which are found in higher proportions in hardwood hemicelluloses) are more susceptible to thermal degradation than hexosans (Fengel and Wegener, 1989). Additionally, hardwoods, in general, have a higher proportion of hemicellulose, and the hemicelluloses of hardwoods also have a higher acetyl content compared to softwoods. 

Dry heat treatment of oak resulted in a decrease in the amount of ellagitannins and a simultaneous increase in ellagic acid the lignan lyoniresinol was unaffected by heat treatment 

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