Polypropylene-based Wood-plastic Composites: Effect of Using a Coupling Agent Derived from a Renewable Resource

In this work, post-consumer polypropylene and wood flour from Pinus elliottii were used to produce wood plastic composites. The effect of polypropylene grafted with itaconic acid used as a coupling agent on mechanical properties, thermal stability and morphology of the composites was investigated and compared with the composite developed with polypropylene grafted with maleic anhydride, commonly used as coupling agent in wood plastic composites. Composites with 30 wt% of wood flour and 2 wt% of coupling agent were produced in a co-rotating twin-screw extruder and after were injection molded. The mechanical properties showed that flexural strength improved on 29% and 35% with addition of polypropylene grafted with itaconic acid and polypropylene grafted with maleic anhydride respectively, when compared with the wood plastic composites without coupling agent. On the other hand, the incorporation of polypropylene grafted with itaconic acid does not change the impact strength values significantly. Additionally, the temperature corresponding to 3 wt% of weight loss determined by thermogravimetry for composites with polypropylene grafted with itaconic acid increased by 14°C when compared with wood plastic composites without coupling agent, while addition of polypropylene grafted with maleic anhydride increased approximately 6°C the composite thermal stability. A morphological study revealed the positive effect of the polypropylene grafted with itaconic acid on the interfacial bonding of recycled polypropylene and wood flour.