Saccharide Alterations in Spruce Wood Due to Thermal and Accelerated Aging Processes

This work is devoted to the changes in polysaccharides in thermally treated wood after its accelerated aging with the aim of its optimal utilization after its original use has ended. Spruce wood samples were treated by the Thermowood process at temperatures of 160 °C, 180 °C, and 210 °C and subjected to accelerated aging in wet mode. The influence of treatment temperature and accelerated aging was monitored by wet chemistry, high-performance liquid chromatography (HPLC), X-ray diffraction (XRD), size exclusion chromatography (SEC), and Fourier-transform infrared spectroscopy (FTIR). During thermal treatment, hemicelluloses are mainly degraded. At the temperature of 210 °C, aromatic compounds formed as degradation products of lignin and hemicelluloses bind to cellulose fibers and increase cellulose yield. Preferential decomposition of the amorphous portion of cellulose leads to an increase in its crystallinity, while higher temperatures cause degradation of the crystal lattice. The degree of polymerization in both cellulose and hemicelluloses decreases due to the cleavage of glycosidic bonds. Accelerated aging does not significantly affect the changes in polysaccharides. The results obtained can be used in the processing of cellulose and hemicelluloses from thermally modified wood at the end of its life cycle in various industrial fields.