The effect of fibre and coupling agent content on the mechanical properties of hemp/polypropylene composites

Composites made from hemp and polypropylene were prepared in order to determine the effect of fibre and coupling agent content on their mechanical properties. The samples were prepared by compression molding after an initial melt blending and homogenization step in an internal batch mixer. Different fibre contents (0, 10, 20 and 30 wt%) and sizes (355 and 500 μm) were used with two coupling agents: maleic anhydride polypropylene (MAPP) pellets and wax. For each case, MAPP concentrations between 0 and 7 wt% (fibre basis) were added to determine the optimum amount maximizing mechanical properties. The fractured surfaces of these composites were investigated by scanning electron microscopic technique (SEM) to investigate the fibre/matrix interfacial bonding. The mechanical properties of the composites were characterized in tensile, torsion, and flexion and the results showed that coupling agent addition has a positive effect on all moduli with an optimum content ranging between 2 and 4 wt%. It was also found that the coupling agent wax was more effective that the pellets.