Heat Treatment of Exterior Particleboard

Describes the effects of post manufacturing heat treatment of phenolic resin bonded particleboard. All measurements were made on laboratory boards that were made to approximate commercial particleboard. The basic composition of the boards were: Thickness: 7/16 inch. Wood Material: Aspen flake core with jack pins flake faces. Resin: Commercial phenolic – 50 percent solids; faces contained 12-1/2 percent resin; core contained 7 percent resin. Sizing: Commercial wax emulsion – 50 percent solids; faces and core contained 0.5 percent wax. Density: 44 lb./cu.ft. Pressure: 400 lb./sq.in. Pressing Temp: 370?F. Press Time: 8 min. Post heat treatment was conducted for 30 minutes, 1 hour and 2 hours at 350?F. and 425?F. and measurements of the dynamic modulus of elasticity, internal bond strength, and thickness swelling based on 2 and 24 hour soaking were made. It was concluded that short heat treatments can improve the performance (i.e., physical properties) of exterior particleboard. Thickness swelling was reduced to a minimum at 0.5 to 1.0 hour of heating time. Modulus of elasticity was not significantly reduced and internal bond strength increased to a maximum at 0.5 hour. It was further concluded that heat treatments caused a relaxation in built-in compressive stress which is reflected by reduced thickness swelling and improved surface smoothness and strength retention after exposure to high humidity.

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