Moisture affects most physical properties of wood. Like other porous materials, wood exhibits sorption hysteresis, i.e. the equilibrium moisture content depends on both ambient climate and moisture history. If equilibrium is attained by desorption, the moisture content is higher than if it is reached by absorption to the same ambient climate. This difference in moisture content between desorption and absorption increases with increasing relative humidity (RH) in the hygroscopic range (0 to ~95 % RH) (Fredriksson and Thybring 2018). In the over-hygroscopic range (~95 to 100 % RH), both moisture content and sorption hysteresis increase due to capillary condensation in the wood structure. According to traditional wood literature, the presence of significant amounts of capillary water indicates that the wood is above the fibre saturation point and cell walls are saturated. However, it is unknown if cell walls are indeed water-saturated or whether sorption hysteresis persists in the over-hygroscopic range.
Keywords: moisture, sorption hysteresis, cell wall water
Authors
Emil Engelund Thybring
University of Copenhagen, Frederiksberg, Denmark
Maria Fredriksson
Login to download the PDF