Recycling and its effects on the physical and mechanical properties of wood fibre reinforced polypropylene composites

This study investigates the effect of recycling/reprocessing on the physical and mechanical properties of composites based-on radiata pine (Pinus Radiata) fibre and polypropylene (PP) with a maleated polypropylene (MAPP) coupling agent, produced using a twin-screw extruder, followed by injection moulding. Composites containing 40wt% fibre and 4wt% MAPP were assessed mechanically and thermally, as well as for moisture absorption after being recycled up to eight times. Both the tensile strength (TS) and Young's modulus (YM) of composites were found to decrease linearly from 41 MPa and 4556 MPa respectively to 31 MPa and 3800 MPa for composites recycled eight times. However, the elongation at break was found to increase with increased recycling due to fibre damage that occurred during reprocessing and the associated reduction of average fibre length, found to decrease from 2.36mm to 0.37mm after recycling eight times. Thermal stability and moisture resistance of composites improved with recycling due to the improvement of interfacial bonding between fibre and matrix.