Recycling of polypropylene-based eco-composites

Renewable resources and recyclable thermoplastic polymers provide an attractive eco-friendly quality as well as environmental sustainability to the resulting natural fibre-reinforced composites. The properties of polypropylene (PP)-based composites reinforced with rice hulls or kenaf fibres were investigated with respect to their recyclability. Rice hulls from rice processing plants and natural lignocellulosic kenaf fibres from the bast of the plant Hibiscus cannabinus represent renewable sources that could be utilized for composites. Maleic anhydride-grafted PP was used as a coupling agent to improve the interfacial adhesion between fillers and matrix. Composites containing 30 wt% reinforcement were manufactured by melt mixing and their mechanical and thermal properties were determined. The composites were then pelletized and reprocessed by melt mixing. Finally, structure/ properties relationships were investigated as a function of the number of reprocessing cycles. Results: It is found that the recycling processes do not induce very significant changes in flexural strength and thermal stability of the composites. In particular PP-based composites reinforced with kenaf fibres are less sensitive to reprocessing cycles with respect to PP-based composites reinforced with rice hulls. Conclusion: The response of PP-based composites reinforced with rice hulls or kenaf fibres is promising since their properties remain almost unchanged after recycling processes. Moreover, the recycled composites are suitable for applications as construction materials for indoor applications. In fact, the flexural strength and modulus of these materials are comparable to those of conventional formaldehyde wood medium-density fibreboards.