The Effect of Hygroscopic Wood Structure on Some Properties of Heat Treated Products Formed with the Thermowood Method

Abstract

Changes were determined for the values ​​of physical and mechanical properties resulting from hygroscopicity in some wood species after heat treatment (HT), and to reveal statistically the relationships between the properties. For this purpose, aspen (Populus tremula) and fir (Abies nordmanniana subsp. bornmuelleriana) species were evaluated for weight loss (WL) during HT as well as water thickness swelling (WTS) and weight and volume change rates upon water imersion. The amounts and density values ​​of longitudinal, radial, tangential, and volumetric contractions and expansions, static bending resistance (MOR) and static bending modulus of elasticity (MOE) were examined. From the results and correlation analysis, it was determined that while WL increased in all variations with HT, the WTS values ​​from the HT samples in water for 24 h decreased with the increase in temperature and time, while water retention was at similar rates in all variations, including UT. At the same time, HT resulted in significant decreases in all density values ​​and contraction and expansion values, and the dimensional stability improved. On the other hand, it was understood that HT did not negatively affect both MOR and MOE resistance values ​​at the 180 °C and 200 °C conditions. These results showed that heat-treated wood products can be a good alternative to avoid problems caused by hygroscopicity under the influence of intense water contact.