Heat treated wood is widely used in indoor and outdoor construction, decoration, and furniture because of its favorable dimensional stability, excellent corrosion resistance, and approximate padauk color. However, with many deficiencies in the existing heat treatment process of wood, such as excessive loss of mechanical strength and timber color being too heavy, this study was conducted to provide a reference during actual production for the feasibility and practical effect of low thermo-vacuum treatments with lower temperatures. Changes in physical and mechanical properties of three kinds of wood-okoume, basswood, and andoung, using the same thermo-vacuum treatment conditions were tested. The three woods were placed in a vacuum carbonization tank at 160℃ and 0 MPa conditions for 3 h. Then the timber was sawn according to experimental requirements with wood density, color deviation, toughness, bending strength, modulus of elasticity in static bending, static hardness, shrinkage, and swelling rate being measured. Results showed that dimensional stability of heat-treated andoung was greatly improved with its volume shrinkage coefficient decreasing 16.00%. Moreover, andoung had an increase in flexural strength and hardness, with increased bending strength (18.00%), hardness of its radial section (19.00%), tangential section (33.00%), and end surface (50.00%). Also, its impact toughness loss was less (24.00%). Overall, low thermo-vacuum treatment could improve dimensional stability of wood as it avoided loss of physical and mechanical properties of the timber.
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Ziqiao et al. (2019) studied this question.