Abstract
Thermal modification (TM) improves the hydrophobicity, dimensional stability, and durability of wood, but TM commonly results in severe color change and mechanical strength loss as wood is treated at higher temperature. In this study, Pterocarpus macrocarpus Kurz wood was thermally modified at moderate temperature (150 °C) and higher temperature (200 °C), and subsequently TM wood at 150 °C was subjected to wax impregnation (WI), the effect of a combination of TM and WI on the hygroscopicity, dimensional stability, and mechanical properties, as well as the micro-structure of wood, were investigated and compared. The results showed that the mass loss of wood was slight at 150 °C TM, while it became severe at 200 °C TM conditions. TM conditions affected the amount of the subsequent wax impregnation; the equilibrium moisture content (EMC), water absorption ratio, and adsorption and absorption swelling of the 150 °C TM + WI group were lower than that of 200 °C TM, and presented the lowest value. Moderate temperature TM could improve the hydrophobicity and dimensional stability of wood, but WI played a key role in the improvement. TM decreased the modulus of rupture (MOR) of wood, while WI improved the MOR. TM increased the modulus of elasticity (MOE) of wood, but WI had little effect on MOE; Scanning electron microscope (SEM) observation showed that the wax was successfully impregnated into the wood interior, and presented an even distribution on the internal surfaces of wood cells; Fourier-transform infrared spectroscopy (FTIR) spectra verified the changes of –OH and C=O after TM and TM + WI, which contributed to decreasing hygroscopicity and improving the dimensional stability of the wood. Impregnated wax improved wood mechanical strength, but decreased the lightness, and deepened the color of wood. The combination of thermal modification at moderate temperature with subsequent wax impregnation is a practical approach for improving wood properties.
Highlights
Wood is a natural and reproducible material
Thermal modification (TM) specimens decreased by 28.32% and 36.16%. These results show that TM decreased the equilibrium moisture content (EMC) of the wood, and the reduction became greater due to more severe TM, which is in agreement with a the wood, and the reduction became greater due to more severe TM, which is in agreement with a previous study [33]
Pterocarpus macrocarpus Kurz wood was thermally modified at 150 ◦ C and 200 ◦ C, and subsequently moderate temperature (150 ◦ C) TM specimens were impregnated with wax
Summary
Wood is a natural and reproducible material. It has been widely used in constructions, buildings, and woodworks, due to its natural advantages, such as high strength-to-weight ratio, insulating properties, sound insulation performance, lack of electrical conductivity, and temperature stability.In contrast, wood has natural defects, such as drying shrinkage, poor dimensional stability, Appl. Wood is a natural and reproducible material. It has been widely used in constructions, buildings, and woodworks, due to its natural advantages, such as high strength-to-weight ratio, insulating properties, sound insulation performance, lack of electrical conductivity, and temperature stability. Wood has natural defects, such as drying shrinkage, poor dimensional stability, Appl. Sci. 2020, 10, 8231 and durability [1,2,3], limiting its extensive utilization. The amount of water, especially the bound water in wood, influences the dimensional stability, and physical and mechanical properties of wood-based products [4]. Wood mainly contains three components: cellulose, hemicellulose, and lignin
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