Medium Density Fiberboard from Mixed Southern Hardwoods

Medium-density fiberboards of acceptable quality were made from a mixture of barky chips from 14 southern hardwoods. Boards made from fiber refined at three different plate clearances did not vary significantly in bending, internal bond (IB), or linear expansion. But, lack of replications and the fact that the refiner was not loaded to capacity caused these results to be inconclusive. Increasing press time from 6.5 to 9.5 minutes did not significantly affect bending, linear expansion, or thickness swell, but did result in an improvement in IB from 64 to 73 psi (0.44-0.50 MPa). Bending properties (MOR and MOE) of the boards were predicted by weighing fiberboard properties for individual species according to the proportion of ovendry chips in the mixture. The averages ranged from 1 % below to 6% above the actual values. IB values were predicted less successfully. Additional predictions based on established regression of bending properties versus dry chip bulk density were also made. A weighted average dry chip bulk density of 11.84 Ib/ft3 (190 kg/m3) yielded values of MOR and MOE from 4% below to 1 % above the actual values. Values of MOR at densities of 0.62 and 0.83 were 3330 and 5550 psi (22.9-38.2 MPa), respectively; corresponding values for MOE were 325,000 and 469,000 psi