Effects of coupling agent on the physical properties of wood-polymer composites

Abstract

Wood-polymer composites based on two Australian commercial timbers, radiata pine (pinus radiata) a soft wood and fast growing plantation timber, and blackbutt (eucalyptus piluliaris), a hard wood which is also a plantation timber, were prepared using the vinyl monomer, methyl methacrylate (MMA).It has been established that polymethyl methacrylate does not form bonds with the hydroxyl groups of the cellulose fibres but simply bulks the void spaces within the wood structure. Coupling agents have been known to increase adhesion of wood fibre to polymer matrix. In this study wood samples were pretreated with the coupling agent, vinyltriacetoxysilane, before impregnation with MMA in order to evaluate the effects of the silane coupling agent on the physical properties of wood-polymer composites.These composites were prepared using a catalyst-accelerator method and the polymerisation process was initiated at room temperature. This method involves the impregnation of wood samples using MMA containing benzoyl peroxide (1%), lauroyl peroxide (0.5%) and the accelerator: N,N-dimethylaniline (0.5%). In contrast to the conventional catalyst-heat method, this method requires no heating in the initiation process and thus results in virtually no loss of monomer.In general, there were improvements in dimensional stabilities (positive effects in both anti-shrink and anti-absorption efficiencies), compressive strength and hardness of silane treated wood-polymer composites. The morphology of the composites was examined using scanning electron microscopy and improved adhesion was evident for composites treated with the coupling agent. Since WPC find greatest use in medium to high unit cost products such as flooring and secondary construction items, improvements in both physical and mechanical properties of WPC would have important implications for the wood industry.