Linear Hygroscopic Expansion of Selected Commercial Particleboards

Sorption isotherms and the hygroscopic expansion of 10 different commercial particleboard types were determined. Isotherms were determined by cyclic exposure of specimens to atmospheres over saturated salt solutions. Linear expansion was determined by means of an optical comparator. All particleboards tested showed large sorption hysteresis and some heat stabilization. The average expansion coefficient of all 10 board types was 0.041 percent per 1 percent moisture content change. The lowest expansion coefficient was 0.010 percent and the highest 0.063 percent per 1 percent. In response to a relative humidity change from 40 to 93 percent the average board would expand 0.4 percent, the board with the lowest expansion coefficient would expand 0.1 percent, and the board with the highest expansion coefficient would expand 0.7 percent. There is some indication that boards made from large flakes have lower expansion coefficients.

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