Dynamic sorption and hygroexpansion of wood subjected to cyclic relative humidity changes

To investigate the behavior of sorption and hygroexpansion of wood at nonequilibrium, Sitka spruce (Picea sitchensis Carr.), 4-mm along the grain and 20-mm in radial and tangential directions, was exposed to sinusoidally RH between 45-75% at 20°C for 1, 6, and 24 h. Moisture changes and radial and tangential dimensional changes measured during the cycling gave the following results: moisture and dimensional changes of the specimens were generally sinusoidal but lagged behind the imposed RH. The phase lag decreased and amplitude increased with increasing cyclic periods. Furthermore, a mathematical model proposed in a previous study was modified to describe the dynamic sorption of wood exposed to cyclical RH. The model not only produced kinetics in good agreement with experiment results, but also can provide moisture gradient distributions developed throughout the wood during cyclical processes.