Processing and bending behavior of wood-plastic laminated timber

Abstract: The mechanical performance of common wood plastic composites was poor and couldnot be used as structural member. Structural wood-plastic laminated timber was prepared with domestic fast-growing poplar wood veneer and thermoplastic plastic alloy by the flat-pressed method. The plastic alloy was composed with polyethylene and polypropylene film with the weight ratio of 1:1 and acting as adhesive in laminated timber. The hot pressing temperature, ranging from the melting temperature of plastic alloy measured by differential scanning calorimeter to the pyrolysis temperature of wood materials, could be determined preliminarily. Secondly the effects of the hot pressing temperature, the wood-plastic ratio and the concentration of maleic anhydride on the bonding strength of wood-plastic laminated timber were studied. Then the tests on the effects of the above 3 factors on the bending behavior of wood-plastic laminated timber were carried out. The results showed that, the interfacial damage mode of wood-plastic laminated timber with coupling agent under tension and shear forces was wood failure, while that of controlled specimens was interfacial delamination between wood and plastic. Compared with controlled specimens, the bonding strength of wood-plastic laminated timber pretreated with coupling agent was the highest, and increased by 16.7% at 180℃, wood-plastic ratio of 3/2 and maleic anhydride concentration of 4%. Wood-plastic laminated timber exhibited better mechanical properties with the flat pressing preparation method, and could be used as a structural wooden member. Bending strength was negatively correlated with modulus of elasticity for wood-plastic laminated timber. In the experiment, bending strength of wood-plastic laminated timber increased with the increasing of the wood density and the ratio of wood to plastic at the density of 0.6 and 0.8 g/cm3, while modulus of elasticity decreased, and the microstructure of wood kept integrated. Compared with the densities of 0.6 and 0.8 g/cm3, wood-plastic laminated timber was stronger at a density of 1.0 g/cm3. Bending strength decreased with the increasing of wood-plastic ratio at the density of 1.0 g/cm3. The resistance of wood-plastic laminated timber increased with the density and the wood-plastic ratio. There was much discontinuous crack at the direction of cross grain of wood veneer, so the structural integrity of wood decreased at a wood-plastic ratio of 3/3. The bending properties of wood-plastic laminated timber met the demands and reached the 100E level according to the national standard of China when the hot-pressing temperature was 190℃, the wood-plastic ratio was 3/2 and 3/3, the concentration of maleic anhydride was 4%, and the density was 0.8 g/cm3. The study may provide valuable information for the structural applications of wood-plastic laminated timber.