Parameters Affecting Dimensional Stability of Flakeboard and Particleboard

In order to determine how various processing parameters affect dimensional stability of flakeboard and particleboard, predictive regression models were devised in terms of linear expansion (.LE), thickness swelling (TS), water adsorption (WA), and the hygroexpansivity ratio (LE/WA). Relative humidity regime, furnish geometry, board specific gravity (SG), and resin type were the variables studied. The flakeboards and particleboards were made of Douglas-fir bonded with urea- or phenol-formaldehyde (PF) adhesive. Regression models for LE/WA and TS were able to predict approximately 88 and 96 percent, respectively, of all variability. Water adsorption, which was determined by the relative humidity regime (30 percent to 65 percent, 65 percent to 80 percent), was the dominant variable, with the other variables studied being of lesser significance. The regression models were used to define optimum conditions for minimum LE and TS in terms of particle geometry, board SG, and resin type. For a flakeboard with an SG of 0.70, the combined optimum for LE and TS occurred for flakes 0.30 mm (0.012 in.) and 20 to 50 mm (0.79 to 1.97 in.) in length. Board dimensional stability could be improved by decreasing SG or using PF adhesive. Whereas, the optimum dimensional stability for particleboard ‘could be obtained by using thin particles 0.15 mm (0.006 in.), by decreasing SG, and by using PF adhesive.

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