Hygroscopic Properties of Six Tree Species with Four Tangential Thicknesses

The differences of hygroscopic property among six tree species with four thicknesses were examined. The density, chemical composition, crystallinity, equilibrium moisture content (EMC), and moisture absorption rate were measured by static saturated salt solution method, and the isothermal moisture absorption curve was fitted by the H-H model to analyze monolayer molecular adsorption and multilayer molecular adsorption. The results show that under the same relative humidity (RH), the EMC of Picea asperata and Populus deltoides were increased with increasing thickness, while that of Quercus spp. and Xanthostemon melanoxylon were decreased. The moisture absorption rate of P. asperata was the largest and that of X. melanoxylon was the smallest. When RH ranged from 0 to 97%, the monolayer molecular adsorption water amount of samples with different thicknesses of the six tree species gradually became close. With the increase of tree species density, the monolayer molecular adsorption water amount of the thinner sample is gradually greater than that of the thicker sample. The change of multi-layer molecular adsorption water content is consistent with that of EMC, Moisture absorption rate, monolayer molecular adsorption water, and multilayer molecular adsorption water are related to the chemical composition content, density, and thickness of tree species.