Analyzing reversible changes in hygroscopicity of thermally modified eucalypt wood from open and closed reactor systems

Abstract

Eucalyptus nitens was thermally modified in either an open or a closed reactor system at different temperatures and water vapor pressures. Reversible changes in equilibrium moisture content (EMC) and volumetric swelling (Smax) were analyzed during cycles that included repeated conditioning at 20 °C/65% RH, water-soaking and vacuum-drying at room temperature. These cycles partially diminished the reduction in EMC and Smax measured directly after the modification process. The recovery of drying-related annealing effects of amorphous polymers was considered the main effect during water-soaking cycles of wood from the open reactor system, while the removal of the cell wall bulking effect was the main effect in the wood modified in the closed system in nearly saturated water vapor. Water-soaking cycles also changed the dynamic vapor sorption behavior to a considerable extent, leading to a lower reduction in EMC by thermal modification over the entire RH range measured. Exposure of the samples to 95% RH during the dynamic vapor sorption measurements was incapable of removing reversible effects to the same extent as repeated water soaking.