Abstract

The object of this study was to measure basic wood properties when water in wood is lost by heating under high temperature and high humidity. Using Sitka spruce (Picea sitchensis Carr.) specimens with dimensions of 110 mm (R)×25 mm (L)×8 mm (T), temperature and weight were measured and free-free flexural vibration tests were conducted in water vapor at 115–150°C and 75–98% relative humidity. The results were compared to those at high temperatures without humidity control under atmospheric pressure. Early in the drying process, the resonance frequency and loss tangent showed a minimum and maximum, respectively. Temporal changes in the temperature, moisture content and vibrational properties were similar to those in heating without humidity control, while the specific Young's modulus and loss tangent during the drying processes were much smaller and greater, respectively, than those in heating without humidity control. Hence, we concluded that the wood was remarkably softened by high temperature and moisture.