Component Variables on Properties of Particleboard for Exterior Use

This study of exterior-type particleboard was designed to evaluate the influence of the major component variables and end-use properties. A “standard” 40 lb./cu.ft. Douglas-fir flakeboard was manufactured, containing 6 percent phenolic resin and 1 percent wax. The uncompressed mat was prepressed at 400 psi and hot pressed at 350?F. After pressing for 15 minutes, the board was cooled, conditioned to equilibrium at 80?F., 65 percent relative humidity, and sanded on both faces. The variables chosen for evaluation were resin and wax content, board density, mat moisture content, flake length and thickness, and particle geometry. In addition, post treatments of paint, paper overlay, and water repellent were included. Boards of redwood, aspen, and southern pine, as well as boards of several special constructions were included. Results show that resin content is the most important single variable affecting exterior performance. At lower resin contents, performance can be improved by increasing the capacity to shed free water–paint, paper overlays, and water repellents are useful. Sanding the surfaces of flakeboards also proved desirable, and thin flakes produced tight faces. Boards made from planer shavings exhibited good thickness swell properties but reduced linear stability. The addition of wax improved weathering resistance, but no differences were detected between 1, 2, or 4 percent wax contents. It was observed that the most severe conditions of environmental exposure were present at Olympia, Wash., while the least severe were at Fresno, Calif. The net effects at the Harrison, Miss. site were less pronounced than those at Olympia but more so than those at Madison, Wis. The ASTM accelerated aging test resulted in thickness swell trends similar to those obtained by soaking in water for 30 days. These trends, however, were not always in agreement with those established in exposure site conditioning.

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