Hygroscopicity of heat-treated Norway spruce (Picea abies) wood

Hygroscopicity of heat-treated spruce wood is investigated in relation to the mass loss that occurs during the thermal treatment. It is found that the reduction in hygroscopicity is not only due to mass loss, but another mechanism exists. It is hypothesized that this mechanism is related to irreversible hydrogen bonding in the course of water movements within the pore system of the cell walls. Regarding batch experiments with constant amount of water and wood, such hornification occurs during a wetting and drying cycle induced by heating to a predetermined steady-state temperature, provided an intermediate relative humidity prevails at the isothermal stage.