Humidity Cycling Effects on Pine Veneer-Particleboard Core Structure Panels

The influence of three repeated high-low RH cycles on dimensional changes and certain mechanical properties of the following three types of structural sandwich panels is presented: a) a three-ply, 7/8-inch-thick panel with 5/8-inch urea particleboard type 1-B-2 for core faced with 1/8-inch southern pine veneers, b) a three-ply, 7/8-inch-thick panel with 5/8-inch phenolic particleboard type 2-B-2 for core faced with 1/8-inch southern pine veneers, and c) a five-ply, 7/8-inch-thick panel with 3/8-inch urea particleboard type 1-B-2 for core faced and crossbanded with 1/8-inch southern pine veneer. Specimens were subjected to the following sequence of RH changes: 65 to 90 to 65 to 30 to 65 percent. Dimensional changes and mechanical properties during and after cycling were determined. The effect of high and low RH cycling on specimens of the three panels was a reduction in stiffness and strength, and an increase in thickness swelling and linear dimensions. The greater reduction in properties and increase in dimensions occurred during the first RH cycle. If we compare the functional properties for single layer floor of the two equal thickness panels, five-ply urea core panel with the three-ply phenolic core, the five-ply is a better functional panel. It is 26 percent stiffer after cycling and remains flat at high RHs.

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