The influence of extractives on the sorption characteristics of Scots pine (Pinus sylvestris L.)

The sorption behaviour of extracted and un-extracted Scots pine (Pinus sylvestris L.) heartwood was analysed using dynamic vapour sorption apparatus. In addition to the sorption isotherm and hysteresis, the moisture increments and decrements were determined as well as the rate of sorption. Parallel exponential kinetics model was used for further analysis. The effect of cyclic humidity loading on the sorption characteristics was studied by exposing samples to ten repeated sorption cycles and by determining the amount of accessible hydroxyl (OH) groups before and after the cyclic humidity loading. Removal of extractives led to an increase in EMC both in adsorption and in desorption. Hysteresis decreased due to the removal of extractives. Cyclic humidity loading reduced the sorptive capacity of wood material for both extracted and un-extracted wood, but was more pronounced in un-extracted wood. However, despite the decrease in the sorptive capacity, the amount of accessible OH groups increased after ten repeated dry-humid cycles.