Effects of extracts on color, dimensional stability, and decay resistance of thermally modified wood

Thermal modification can change the color and improve the dimensional stability and decay resistance of wood without the use of chemical modifiers. However, the impact of extracts from thermally modified wood (TMW) on the performance of TMW remains obscured. To achieve high-value utilization of TMW extracts and to regulate the properties of the TMW through extracts, the impacts of TMW acetone extracts on the color, dimensional stability, and decay resistance of TMW were investigated. The 180, 200 and 220 °C thermally modified spruce ( Picea asperata Mast.) and poplar ( Populus tomentosa Carr.) with or without acetone extract were used for CIELab color system, anti-swelling efficiency (ASE), and decay resistance assessments. Fourier infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to characterize extracted and unextracted TMW. The results indicated that the extract showed positive effects on the color, dimensional stability (220 °C), and decay resistance of TMW, and this effect weakened with increasing temperature. The removal of the extract resulted in a reduction in brightness difference ( ∆L* ) and total color difference ( ∆E* ) of the TMW, with the most pronounced impact observed at 180 °C. The removal of the extract enhanced the dimensional stability of the TMW at 180 and 200 °C but decreased it at 220 °C. The decay resistance of wood thermally modified at 180, 200, and 220 C decreased after extraction, and was most significant at 180 °C. The antifungal activity of the extract was related to the production of vanillin, isovanillic acid, syringic acid, and syringaldehyde. Extract from TMW played an important role in the properties of TMW, serving as a potential means for adjusting its properties or as a natural wood modifier.