Thermal Modification Intensity of Heat-treated Poplar Wood. Part 2: Characterization and Predication from Outside to Core Layers

Based on the previous study of the heat-treated wood at 0-3 mm surface layer, this study focuses on the transition of thermal modification intensity on 160-220 °C heat-treated poplar from surface to core layers. The color change was evaluated by CIELAB, and surface hardness was detected via Shore D (HD) and pressing ball method (HR); furthermore, the FT-IR was applied to detect the thermal degradation of wood components. The results show that the degradation of cell wall components in the surface layer of heat-treated poplar wood is greater than that in the core layers, and the thermal degradation intensity of the surface layer of the heat-treated poplar wood is greater than that of the other inner layers. Surface color and hardness properties of the heat-treated wood between S0 and S1-S5 test surfaces were significantly different under the same heat treatment conditions; the surface hardness showed an increasing trend, and the HR value of the H220-2 core layer was 105.71 % higher than that of the surface layer. Heat treatment temperature is the main factor affecting the property of wood surface, while the effect of duration is smaller. The hemicellulose content change was mainly related to the degradation intensity on heattreated wood at different locations. An accurate prediction model of surface color, hardness, and other properties of the heat-treated wood at different locations was established by Table Curve 3D software.