Determination of some physical and mechanical properties of heat treated and thermo-mechanical densified eastern spruce (Picea orientalis) and black poplar (Populus nigra) woods

In this study, it was aimed to determine some physical, mechanical and technological properties of thermo-mechanical densified wood materials after heat treatment at different temperatures and durations. Specimens prepared from Eastern spruce (Picea Orientalis) and black poplar (Populus nigra) woods were subjected to heat treatment in atmospheric pressure environment at four different temperatures (140 °C, 160 °C, 180 °C and 200 °C) and two different duration (7 and 9 h). Heat-treated samples were then densified using a hydraulic press at 150 °C with compression ratios of 20% and 40%. In the test specimens, the spring-back ratio, air-dry density, water absorption and compression direction (radial) swelling ratio were performed to determine the physical properties while static bending strength, modulus of elasticity, compression strength parallel to fibers and Brinell hardness tests were performed in order to determine mechanical properties. According to the results of the study, the density and mechanical strength properties of the heat treated specimens decreased in general due to the increase in the process temperature and duration. In the densified specimens, the spring-back and the water absorption decreased due to the heat pre-treatments and an improvement of up to 60% in dimensional stability was achieved. On the other hand, in heat treated specimens where strength losses occurred, density, mechanical strength and hardness properties after densification modification demonstrated a significant increase depending on compression ratio. According to the obtained results, it can be suggested to use these two methods together in order to eliminate the negative effects of both heat treatment and densification modification on the wood material. Keywords: Wood material, Physical and mechanical properties, Heat treatment, Densification.