A NEW METHOD FOR OBTAINING HIGH STRENGTH PHENOL FORMALDEHYDE RESIN-IMPREGNATED WOOD COMPOSITES AT LOW PRESSING PRESSURE

To obtain high strength phenol formaldehyde (PF) resin-impregnated compressed wood at low pressure, we investigated the effects of sodium chlorite treatment followed by sodium hydroxide treatment prior to low molecular weight PF resin impregnation. Sawn veneers of Japanese cedar (Cryptomeria japonica) were first treated with 2% aqueous solution of NaClO2 followed by 0.5% aqueous solution of NaOH. A total weight loss of 12% was obtained by the combination of these two treatments. It was found that the treatments showed potential for the marked deformation of PF resin-impregnated wood at low pressure. The result suggests that depolymerization or partial removal of lignin can be effective for the removal of hemicellulose, which softens the cell wall swollen by PF resin and makes it possible to compress wood remarkably at low pressing pressure. Pressure holding during compression caused creep deformation of resin-impregnated wood and resulted in density, Young’s modulus (MOE) and bending strength (MOR) of 1.16 g cm-3, 29 GPa and 307 MPa respectively at a pressing pressure of 1 MPa. This technique imparts high strength and attractive surface to plywood and other wood composite materials with conventional hot press equipment.