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

Thermal modification can enhance the color as well as improve the dimensional stability and decay resistance of wood without the use of chemical modifier, but the impact of extracts from thermally modified wood (TMW) on performance remains unclear. In order to utilize extracts to regulate the properties of the TMW or prepare the imitate TWM without mechanical loss, the effects of TMW acetone extracts on the color, dimensional stability, and decay resistance of TMW were investigated. The 180°C, 200°C and 220°C thermally modified spruce ( Picea asperata Mast.) and poplar ( Populus tomentosa Carr.)with or without acetone extract were used for CIELab system, anti-swelling efficiency(ASE), and decay resistance test. 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 the increase of temperature. The brightness difference ( ∆L* ) and the total color difference ( ∆E* ) of the TMW were reduced due to the removal of the extract, and the wood thermally modified at 180°C was the most significant. The removal of the extract will lead to the improvement of the dimensional stability of the TMW at 180°C and 200°C and the reduction of the TMW at 220°C. The decay resistance of wood thermally modified at 180°C, 200°C, 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, and can be used to adjust its properties or as a natural wood modifier.