Characterization of wood-polypropylene composite sandwich system

A new wood-polypropylene composite sandwich was made by bonding unidirectio nal continuous glass fiber reinforced polypropylene (UCGPP) composite to oa k wood using a thermoplastic tie layer. In order to evaluate the practical utility of wood-composite sandwich systems, the effects of moisture changes in both continuous and cyclic manner were investigated by monitoring the m odulus change. Dynamic mechanical analysis (DMA) of neat wood and wood-comp osite sandwich was carried out under controlled relative humidity (RH) and isothermal conditions to simulate moisture desorption/sorption processes. I t is observed that under continuous desorption condition the modulus increa se is less in the case of wood-sandwich (20%) when compared with neat wood (35%). However, under desorption/sorption cycle conditions the wood-sandwic h undergoes significant modulus change when compared with neat wood. It is inferred that while bonding wood with UCGPP composite helps reduce the vari ation in modulus under continuous desorption, it is not the case under cycl ic moisture condition. The modulus behavior of both dry and normal wood-san dwiches at different end-use temperatures is also studied using DMA. Optica l and environmental scanning electron micrographs show the distribution and penetration pattern of tie layer into wood as well as UCGPP composite, thu s demonstrating the significance of micro-mechanical interlocking for bondi ng.