Effect of Flake Dimensions on Properties of Particle Board

The study was made to provide information on the interrelationships of wood particle shape and a variety of board properties. Study variables included Douglas-fir flakes on levels of 0.65, 0.75, and 0.85 specific gravity; 1/2-, 1,- 2,- and 4-inch flake lengths; and 0.009, 0.012, 0.015, and 0.018 inch flake thicknesses; with resin levels of 3 and 5 percent. This combination of variables provided an experiment having a 3 x 4 x 4 x 2 factorial design. Three replications of each treatment combination were employed to provide a reasonable measure of the within-treatment variance. One-inch, rough, green, Douglas-fir lumber was flaked and segregated into 16 combinations of flake thickness and length. Each pile was dried to 5 percent moisture content and screened to eliminate fines. The test batches of flakes were sprayed with Amres 7500 and Paracol 404N and pressed into 1/2-inch boards of 0.65, 0.75, and 0.85 specific gravity. After pressing, the boards were conditioned at 70?F. and 50 percent relative humidity, and each board was sawn into suitable pieces for testing. Results were: 1) Modulus of Rupture.–Thickness: No significant difference between boards made from the four thicknesses of flakes. Length: Boards with 1/2-inch flakes were significantly poorer in bending strength than the remaining boards. Comparison between the remaining boards was not significant. 2) Internal Bond Strength.–Thickness: Boards with 0.009-inch flakes were significantly weaker than the remaining boards. Strength of boards increased as flake thickness increased. Length: Boards with 1/2-inch flakes were significantly stronger than the remaining boards. No statistical difference in strength between the remaining boards. Thickness Swell.–Thickness: After 2-hour immersion in water, no significant difference between boards containing the four flake thicknesses. After 24-hr. immersion, 0.009- inch flake boards swelled significantly less than the remaining boards. Length: After 2- and 24-hr. immersion, 1/2-inch flake boards swelled significantly greater than the remaining boards. Same results, to a lesser degree, for 1-inch flake boards compared to 2- and 4-inch flakes. 4) Water Absorption.–Thickness: After 2- and 24-hr. immersion, no significant difference between any of the boards. Length: After 2- and 24-hr. immersion, significantly greater absorption by 1/2-inch flake boards. 5) Linear Expansion.–Thickness: Boards with thicker flakes had significantly greater expansion. Length: Significantly greater expansion in 1/2-inch flake boards. 6) Length-Thickness Ratio.–Cannot completely predict the effect of flake dimensions on board properties. Optimum ratio: 150 – 250.

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