Evaluation of the mechanical properties of injection moulded hemp fibre reinforced polypropylene composites

In recent years, industrial hemp fibre reinforced thermoplastic composites have attracted substantial interest as potential structural materials. These composites have been subject to intense study for use in lightweight, recyclable and low cost applications. The aim of this research was to improve and evaluate the composite tensile strength and fibre/matrix interfacial adhesion by means of fibre treatment and addition of a coupling agent. Hemp fibre was digested in a small pressure vessel with a solution of 5wt% NaOH / 2wt% Na2SO3. Single fibre tensile tests were performed on treated and untreated fibres, and it was found that the alkali treatment resulted in an increase in fibre strength and an improvement in fibre separation. Composites containing either treated or untreated fibre, polypropylene and a maleic anhydride modified polypropylene (MAPP) coupling agent were then compounded in a twin-screw extruder and injection moulded into tensile test specimens. Tensile tests revealed that significant improvements in composite strength were made by using treated fibre and MAPP. The effect of MAPP on the interface of treated hemp fibre/polypropylene composites was assessed by means of the single fibre fragmentation test, and the interfacial shear strength was determined thereafter.