Effects of manufacturing parameters on the linear expansion of densified wood composite panels II. Effect of board density, resin type and resin content on linear expansion of particleboard

The objective was to determine the relationship between the variables board density, resin type, and resin content and the dimensional stability prope rties of particleboard. Manufactured boards were exposed to three levels of relative humidity (RH) and to a vacuum-water-soak treatment. Changes in mo isture content (MC), linear expansion (LE), and thickness swelling (TS) wer e measured. Results obtained are summarized as follows. 1) Equilibrium moisture content (EMC) decreased as board density and resin content increased at all levels of exposure. EMC of methylene diphenyl diis ocyanate (MDI) resin board showed the lowest value and phenol-formaldehyded e (PF) resin board showed the highest value at the 95% RH exposure level. 2) Increases in board density increased LE per unit of moisture content cha nge (LE/MC) and TS per unit of moisture content change (TS/MC). The influen ce of resin type on LE/MC was not clear at 66% RH, but at 95% RH, PF showed the lowest value of LE/MC. Decreases in resin content increased TS, howeve r LE tended to decrease slightly. 3) Multiple regression analysis shelved that LE/MC could be predicted with TS/MC, board density, and internal bond strength (IB) as the explanatory va riables. 4) When exposed to an alternate vacuum-water soak and oven-drying treatment , TS increased, however LE decreased with increasing number of cycles, exce pt for the urea-formaldehyde (UF) board. Except for the UF board, the board length in the dry condition gradually became less than the initial length. PF resin showed superior dimensional stability.