Comparison of thermal modification method with air and oil on physical and mechanical properties of Paulownia wood

One of the ways to supply wood raw material is to plant fast-growing species, with regards to the lack of forest resources and the increase in demand for wood and its products. One of the fast-growing species cultivated in our country is Paulownia fortune, which has unique characteristics. Nowadays these valuable materials are modified in various ways, due to the importance of optimal use of wood in various applications.. Thermal modification, as an efficient and environmentally friendly method, is a suitable option for improving the characteristics of fast-growing wood species. Therefore, in this study, the effect of thermal treatment in air and oil on some physical and mechanical properties of Paulownia fortunei wood was investigated. The wood used in this research was three trunks of Paulownia tree (Paulownia fortune) from Shasat Kalate forest of Gorgan University of Agricultural Sciences and Natural Resources. The wood was dried in the open air after turning into boards. Then wooden samples with straight fibers and flawless appearance were prepared from them. The samples were modified by two thermal modification methods in air and oil. Thermal modification in air was done according to Thermo-D process (at 212 ± 3 ◦C and 2 hours). Also, thermal modification with rapeseed oil was used for the treatment of samples with the same temperature conditions as the method of thermal modification in air. Then colorimetric test, bending strength, hardness, impact resistance, water absorption and thickness shrinkage tests were performed on the samples. Results revealed that heat treatment with both methods had a significant effect on density, volumetric shrinkage and water absorption, colorimetry, impact resistance, hardness resistance, modulus of rupture and modulus of elasticity. In general, heat treatment with both methods caused a decrease in density, water absorption and elongation, brightness index, impact resistance, hardness, modulus of rupture and modulus of elasticity. The density, water absorption and volumetric shrinkage of the samples treated in oil were higher compared to the samples treated in air. The impact resistance, hardness resistance, modulus of rupture and modulus of elasticity of the samples treated in oil were significantly higher compared to the samples treated in air. In general, Paulownia fortune treated in oil showed relatively better physical and mechanical properties compared to the one treated in air. Therefore, heat treatment in oil is a more effective method to improve the physical and mechanical properties of Paulownia fortune wood compared to heat treatment in air.