Dimensional Stability of Oak Flake Board as Affected By Particle Geometry and Resin Spread

The boards used in this study contained 3.27, 6.54, and 13.07 grams of resin solids per square meter. Panels were composed of oak flakes that were 0.006, 0.012, 0.025, and 0.050 inch thick, and flake lengths of 0.5, 1, 2, and 4 inches. Specimens were conditioned to constant weight in atmospheres of 15, 21, 83, and 92 percent R.H. at 90?F. (corresponding to 3.3, 4.5, 16.8, and 21.3 EMC, respectively). The results show that up to an equilibrium moisture content of about 15 percent, flake thickness had very little effect on stability and that the greatest effect of flake thickness occurred between 16 and 21 percent equilibrium moisture content. Flake thickness had a much more important effect than either flake length or resin spread. From a practical standpoint, it appears that any board which will not be subjected to conditions above 16 percent equilibrium moisture content can be manufactured with thicker flakes. Thickness dimensional changes will be no more of a problem in thick-flake boards than if thinner, more expensive particles are used. If higher equilibrium moisture content conditions are to be encountered, it is clear that the thinner flakes and higher resin spreads will produce the most stable product. Dimensional changes beyond 83 percent relative humidity, at 90?F., were extreme, apparently due to complete release of internal forces inherent in the compressed mass of wood particles, known as springback.

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