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 degreesC. A pressurized chamber was constructed for this purpose. At 50 degreesC, equilibrium moisture content (EMC) behavior deviated only slightly from predictions based on the published data for Sitka spruce. At 160 degreesC, the sorption behavior was distinctly different from the 50 degreesC 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 degreesC, juvenile wood tended to equilibrate at a higher moisture content than mature wood. At 160 degreesC, 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 degreesC.