Hygroscopic Thickness Swelling and Related Properties of Selected Commercial Particleboards

Thickness swelling as a result of cyclic exposure to various relative humidity conditions of ten commercial particleboards was determined. An exposure cycle of 40 – 93 – 40 percent relative humidity resulted in thickness swelling from 5.5 to 15 percent depending on board type. The nonrecoverable portion of this thickness swelling varied from about 1/3 to 1/2 of the total. Most of the thickness swelling occurred at relative humidities in excess of 80 percent. No correlation was found between board density and thickness swelling. Strong positive correlations could be established between the ratio of volumetric expansion over water volume absorbed and nonrecoverable thickness swelling, surface deterioration due to water soaking, and loss of stiffness. These corollary results suggest that density variations in the plane of the board lead to swelling stresses and partial failures during exposure to high humidity.

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