Properties of Structural Particleboards

Phenolic-bonded particleboards were made to study effects of particle geometry, resin content, and panel density on strength, durability, and, dimensional stability properties. All panels were 1/2 by 24 by 28 inches in size and pressed for 10 minutes at 350?F. Flake lengths of 1/2, 1, and 2 inches, thicknesses of 0.015 to 1.045 inch, resin contents of 3 to 9 percent, and panel densities of 37.5 to 52.5 pcf were studied. Most panels were of homogeneous construction, but several three-layer panels and panels with oriented-flake construction or veneer faces also were prepared. A resin spread of 1 pound of resin solids per 1,000 square feet of flake surface area was found to be an optimum level for overall panel properties. Optimum durability (as determined from ASTM D 1037 accelerated aging), strength, and stability properties were obtained from panels made of large, thin flakes (2 inches by 9.02 inch), 5 to 6 percent phenolic resin, 1 percent wax, and pressed to 37.5 to 42.5 percent. A 42.5 pcf panel with 5 percent resin had the following properties with percent of strength retention after accelerated aging shown in parentheses: bending strength = 4,880 psi (85), stiffness = 663,000 psi (91), and internal bond = 102 psi (65). Panels of equivalent properties were produced using high-quality flakes only on the surfaces and using lower quality flakes as core material. Use of long flakes also resulted in linear expansion values in the range of 0.09 to 0.12 percent in 30 to 90 percent relative humidity exposure. Use of 0.045-inch thick flakes improved resin spread, but panels of lower strength and durability resulted. Panels with increased bending strength and stiffness in one panel direction were obtained by orienting the flakes on panel surfaces or by applying veneer overlays at time of pressing. In the direction of flake orientation or veneer grain direction, bending strengths of 6,550 to 13,380 psi; and apparent stiffness values of 1,202,000 to 2,009,000 psi were obtained. This panel construction did sacrifice some strength in the alternate panel direction.

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