Dynamic sorption and hygroexpansion of wood by humidity cyclically changing effect

In order to investigate dynamic sorptive and hygroexpansive behavior of wood under cyclic relative humidity condition,poplar(populus euramericana Cv)specimens,in the size of 20mm(T)×20mm(R)×4mm(L)and 20mm(T)×20mm(R)×10mm(L),were exposed to sinusoidally relative humidity between 45%-75%at 25℃for 1,6,and 24h.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 humidity.The phase lag decreased and the amplitude increased with increasing cyclic periods,while specimen thickness had an opposite effect on the phase lag and amplitude.Under dynamic conditions,the specimens showed sorption hysteresis and swelling hysteresis as well,and moisture sorption coefficient and humidity expansion coefficient of them were in positively correlation with cyclic period, but inversely related to specimens thickness.The dynamic sorption model proposed by aprevious study based on softwood obtained good agreement with experiment results in this study for hardwood species and different specimen thickness.