Chemical changes of polysaccharides in heat-treated European beech wood

This work deals with the influence of different heat treatment temperatures (140, 150, 160, 170, 180, 190, 200, and 210 °C) on changes in sapwood and red heartwood of European beech (Fagus sylvatica L.). According to the results of wet chemistry methods, HPLC (high-performance liquid chromatography), FTIR (Fourier transform infrared spectroscopy), SEC (size exclusion chromatography), the wood constituents in sapwood and red heartwood behaved similarly to heat treatment, but the individual proportions were different. The loss of hemicelluloses and the increase in extractives with increasing temperature were more pronounced in sapwood. The amount of cellulose in sapwood and red heartwood showed similar behaviour with increasing temperature. Thermal treatment causes changes in cellulose crystallinity, and the formation of aromatic structures, mainly in beech sapwood. However, the increase in the lignin content of red heartwood was significantly lower than that of sapwood due to its auto condensation, and formation of pseudo-lignin. Among the carbohydrates, the most significant changes were observed in xylose content, which was almost twice as high in red heartwood as in sapwood. Other carbohydrates (glucose, mannose, galactose, and arabinose) reached similar values in sapwood and red heartwood.