Dynamic Sorption and Hygroexpansion of Wood Subjected to Cyclic Relative Humidity Changes. II. Effect of Temperature

To investigate the effect of temperature on the dynamic sorptive and hygroexpansive behavior of wood, poplar (Populus euramericana cv.) specimens, 20 mm in radial (R) and tangential (T) directions with two thicknesses of 4 mm and 10 mm along the grain, were exposed to a sinusoidally varying relative humidity between 45 and 75% for 1, 6, and 24 h at 25 and 40 °C. Moisture changes, as well as radial and tangential dimensional changes measured during cycling, produced the following results: moisture and dimensional changes in the specimens were generally sinusoidal, and an increase in temperature led to decreased moisture contents and transverse dimensions, accordingly. The amplitude of moisture and dimensional changes was in positive correlation with temperature, while the phase lag was inversely related to temperature. Sorption hysteresis and swelling hysteresis decreased as temperature increased. Both moisture sorption coefficient (MSC) and humidity expansion coefficient (HEC) were supposed to share the approximate value for different thick specimens if cyclic period is sufficiently long. Transverse anisotropy could be found under dynamic conditions, and the T/R was about 1.65 to 1.75, varying sinusoidally with a phase difference of about a half cycle to the imposed relative humidity.

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