High-temperature drying of scots pine. A comparison between HT- and LT-drying

In order to study the influence of high temperature on wood properties, boards from Scots pine were dried at three different schedules, two high-temperature-schedules (HT) and one at low temperature (LT). Strength properties as hardness, cleavage- and shear-strength were determined and sorption/desorption behaviour were studied. Material was analysed concerning carbohydrate and extractive content and mould growth test at wooden surfaces. Results showed a significant influence of temperature on decreasing shear strength and equilibrium moisture content (EMC) in sorption/desorption tests. Sorption/desorption tests resulted in up to 2.4% lower EMC for HT dried material at the same climate compared with LT-dried and the hysteresis effect seems to be more pronounced in HT-dried material. Mould growth test showed an inhibiting effect of HT-drying on mould susceptibility at wooden surfaces. Carbohydrate analysis revealed a lower content of hemicelluloses in HT-dried boards which indicates a decomposition of the hemicelluloses explaining the decrease in shear strength and hygroskopic moisture uptake seen in the HT dried boards.