The sorption properties of some thermally treated hardwoods analysed by thermodynamics, surface fractality and FT-NIR spectroscopy

The sorption-­- and chemical properties of ash-­- and beech wood after industrial heat treatment in a water-­-vapour atmosphere were analysed by sorption thermodynamics, adsorbing surface fractality from sorption isotherms and by FT-­-NIR spectroscopy. A considerable reduction in water vapour sorption capacity after heat treatment of wood was confirmed for both wood species, more significantly in beech wood in the middle hygroscopic range. The fractal dimension of the internal adsorbing wood surfaces increased with the amount of sorbed water and also after thermal processing. FT-­-NIR spectroscopy highlighted that the most significant differences in chemical properties were in the hemicelluloses and revealed regions and bands, where considerable changes appeared due to changed water sorption characteristics of heat-­-treated ash-­- and beech wood.