Equilibrium Moisture Content of Wood in High-Temperature Pressurized Environments

Experiments were conducted on the water sorption characteristics of three wood species, for both juvenile wood and mature wood, at conditions above and below 100°C. A pressurized chamber was constructed for this purpose. At 50°C, equilibrium moisture content (EMC) behavior deviated only slightly from predictions based on the published data for Sitka spruce. At 160°C, the sorption behavior was distinctly different from the 50°C data, or any extrapolation from published low-temperature data. The data suggested that a change in the sorptive properties of the wood occurred as temperature and moisture conditions exceeded the glass transition temperature for lignin. At 50°C, juvenile wood tended to equilibrate at a higher moisture content than mature wood. At 160°C, however, juvenile wood exhibited a markedly lower EMC than mature wood. Thermal degradation of wood was detected during the experiments. Reduction in the sorptive behavior as a result of thermal degradation is proposed as a possible explanation for differences in EMC behavior for juvenile and mature wood at 160°C.