Effects of cyclic patterns of relative humidity on moisture sorption of Populus euramericana

Moisture changes during cyclic fluctuations of relative humidity (RH) usually affects wood service. To investigate the effects of different cyclic patterns of RH fluctuations on wood sorption, Populus euramericana was subjected to three dynamic sorption modes and a static adsorption-desorption loop. Moisture responses were measured automatically. Regarding the sorption amount, the average moisture content (MC), amplitude, and moisture sorption coefficient in a square pattern of humidity change were larger than those obtained from sinusoidal or triangular patterns, but all were less than those experienced in the static humid condition. For the sorption rate, the maximum phase lag was in the square pattern, and the corresponding value from sinusoidal pattern was about 1.5 times of that in the triangular pattern. The greatest dynamic diffusion coefficient (D) was also in square pattern, but less than the static value. Sorption kinetics were characterized by a mathematical model, which indicated that the highest dynamic MC gradient difference between center and surface was lower than that under the static condition, in the following order: square pattern > sinusoidal pattern > triangular pattern. The results could help with understanding the effects of cyclic RH changes on moisture change and the potential deformation during wood service.