Effects of element size and orientation in the production of high strength resin impregnated wood based materials

The effects of low molecular weight phenolic resin impregnation and high pressure hot pressing (150 degrees C, 30-100 MPa) on the physical and mechanical properties of wood were first investigated by using sawn wood prepared from a block of Japanese birch (Betula meximowicziana). Subsequently, the effects of element size and orientation were examined by using sliced veneers, particles and powder prepared from the remaining portion of the block. Due to the combination of resin impregnation and hot pressing under high pressure, the specific bending strength at 20 degrees C and 65 % RH of sawn wood increased 50 % accompanied by enormous decreases in moisture content, and bending strength reached around 400 MPa. The mechanical properties of veneer laminated product did not differ significantly from those of sawn wood product. Among isotropic products, the highest bending strength at 20 degrees C and 65 % RH of plywood, par ticleboard and powderboard was 242 MPa, 166 MPa and 175 MPa, respectively. The difference of bending strength between plywood and other isotropic products could be explained by the difference in element orientation, cross lamination and random distribution. Furthermore, the results for the particleboard and powderboard showed that when the resin impregnated elements were hot pressed under high pressure, a decrease in element size did not result in a decrease in bending strength.