Effects of cyclic drying and moistening on the mechanical and physical properties of wood

Most wood products often undergo continuous changes in moisture condition caused by the surrounding environment. However, few studies have conducted experiments to verify the effect of cyclic changes in moisture condition on the macroscopic mechanical and physical properties of wood. In this study, two types of cyclic drying and moistening were repeatedly applied to Japanese cedar (Cryptomeria japonica D. Don) specimens to understand the effects of cyclic changes in moisture condition on the mechanical and physical properties of wood: one involved heating, and the other involved no heating during each treatment. After seven cycles of each treatment, their effects on mechanical and physical properties were verified. Material tests indicated that reductions in the resistance to shearing force were due to cyclic drying and moistening, regardless of heating in treatments. In addition, increases in strain energies, which indicated the occurrence of toughness enhancement, were due to drying and moistening without heating. Decreases in L* and increases in mass loss were also due to cyclic drying and moistening, regardless of heating. FTIR spectroscopy suggested that increases in cellulose crystallinity in microscopic regions in wood cell walls were due to cyclic drying and moistening.