Water sorption hysteresis in wood: I review and experimental patterns - geometric characteristics of scanning curves

The origin of sorption hysteresis in the wood-water system is still under debate. In nanoporous-fluid systems, in general, hysteresis is explained as the manifestation of metastable states in a single pore-fluid system and that is further complicated by the pore connectivity. Cell walls are considered as micro-mesoporous materials and capillary condensation in the entire hygroscopic region is proposed as an alternative sorption mechanism. In the present work, the woods of Douglas-fir, aspen and western red cedar were in focus and the pore connectivity has been investigated by observing five experimentally generated hysteresis patterns comprised by up to 4th scanning curves at 25 and 40 degrees C. Special attention was given to the congruency property from one pattern as it is known from the literature that deviation from this property can reveal the extent of pore connectivity. Consistent patterns were found for the species-temperature combinations. Further, the high extent of congruency property indicated the dominance of independent cell wall pores.