Characterization of Wood Surface Elemental Compositions after Thermo-vacuum Treatment and Superheated-steam Heat Treatment

This research investigates the mechanisms behind color changes, hygroscopicity reduction, and mechanical strength loss in pine wood (Pinus kesiya var. langbianensis) and birch wood (Betula alnoides). Elemental composition changes to the surfaces of pine wood and birch wood that had undergone high-temperature heat treatment were investigated with X-ray photoelectron spectroscopy. The O/C (oxygen/carbon) ratios of the wood surfaces were reduced after the thermo-vacuum and superheated steam heat treatments, which indicated a decrease in the amount of oxygen-containing functional groups. The content of C1 (carbon atoms bonded to carbon or hydrogen atoms) increased, and that of C2 (carbon atoms bonded to one oxygen atom) decreased after the thermo-vacuum and superheated steam heat treatments. The results also indicated that the relative lignin content increased and the hydroxyl group (-OH) content in the cellulose and hemicellulose decreased. The ratio of O2 (oxygen atoms bonded to carbon atoms with a double bond) to O1 (oxygen atoms bonded to carbon atoms with a single bond) increased remarkably. Thus, the content of carbonyl groups in the lignin increased.