Characterization of Wood-Polypropylene Composite Sandwich System

Abstract

A new wood-polypropylene composite sandwich was made by bonding unidirectional continuous glass fiber reinforced polypropylene (UCGPP) composite to oak 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 modulus change. Dynamic mechanical analysis (DMA) of neat wood and wood-composite sandwich was carried out under controlled relative humidity (RH) and isothermal conditions to simulate moisture desorption/sorption processes. It is observed that under continuous desorption condition the modulus increase is less in the case of wood-sandwich (20%) when compared with neat wood (35%). However, under desorption/sorption cycle conditions the wood-sandwich undergoes significant modulus change when compared with neat wood. It is inferred that while bonding wood with UCGPP composite helps reduce the variation in modulus under continuous desorption, it is not the case under cyclic moisture condition. The modulus behavior of both dry and normal wood-sandwiches at different end-use temperatures is also studied using DMA. Optical and environmental scanning electron micrographs show the distribution and penetration pattern of tie layer into wood as well as UCGPP composite, thus demonstrating the significance of micro-mechanical interlocking for bonding.