The effect of cyclic relative humidity changes on moisture content and thickness swelling behavior of oriented strandboard

This study examines the effect of cyclic RH exposure on MC and thickness swelling (TS) of oriented strandboard (OSB) made from fire-impacted trees. Two specimens were cut from the center of each OSB panel and one was edge-sealed. After being conditioned to 65% RH, specimens were placed in a climate-controlled chamber and subjected to three cyclic changes of 90-30% RH at 20°C. Experimental data were characterized by three time-dependent MC or TS models: logarithmic, power law, and exponential. The latter two models gave the best fits showing that edge-sealing reduced the extent of swelling during adsorption and reduced the moisture loss at desorption. The models also described the effect of burnt level and bark throughout the humidity exposure cycles. The exponential model revealed no significant effect of burnt level on the panel TS. Both the power law and exponential models indicated that addition of charred bark to the panels significantly decreased the maximum amount of moisture and thickness change. The exponential model revealed an increase in equilibrium TS at the end of each RH cycle compared with the end of precyclic desorption. True nonrecoverable TS was difficult to discern in Cycle 1 because of moisture hysteresis, but the nonrecoverable effect was evident in Cycles 2 and 3.