Tribological properties of hemp fiber reinforced polylactic acid bio-composites: effect of different types of modification methods

Abstract

In this study, green composites are prepared with 30 wt.% hemp fibers reinforced polylactic acid (PLA) to enhance impact and tribological properties. Different surface treatments of alkali and silane, compatibilizer of maleic anhydride (MA), and blends of thermoplastic polyurethane (TPU) and poly (butylene succinate) (PBS) were applied to improve interfacial adhesion between fibers and matrix. Hemp reinforced PLA bio-composites were fabricated and characterized by hardness, impact strength, wear and friction properties. The tribological tests of the injection-molded components were performed under two different loads (10N and 20N) as dry-sliding linearly reciprocating motion per ASTM G133. Modified composites gave better tribological properties than unmodified composite. While no remarkable improvement was observed in the hardness value of untreated fiber reinforced composite, alkali treated composite reached up to 43% improvement in hardness value. In general, as the load increased, an increase in weight loss was observed in all composites. Unmodified bio-composite exhibited a very low weight loss, and specific wear rate (SWR) compared to neat PLA under 10N load. The SWR of the MA bio-composite had the lowest value for both loads (10N and 20N) compared to the other bio-samples. The TPU blended biocomposite exhibited the highest impact strength (22.96 kJ/m2) after pure PLA (26.5 kJ/m2). Therefore, due to surface treatments and blends applied to the fibers, some composites' hardness and wear resistance were increased while the impact strength and friction coefficient was decreased. Especially silane surface treatment and maleic anhydride compatibilizer application increased the wear resistance of composites. When the Scanning electron microscope (SEM-EDX) images were examined, it was revealed that the fiber and matrix interface bonding was good, and the fibers were firmly embedded in the matrix. Furthermore, forming a protective thin film layer formed by the polymer debris from the surface during dry-sliding increased the wear performance of the bio-composites.