Effects of recycling and hygrothermal environment on mechanical properties of thermoplastic composites

Abstract

Recyclability of nine types of composites including natural and mineral fillers in polypropylene and nylon matrix have been studied through injection molding and mechanical grinding. No significant degradation in mechanical properties of natural fiber composites occurred after recycling or water absorption tests. In contrast, glass fiber composites showed decrease in tensile strength and modulus by up to 45% and 40%, respectively after five rounds of recycling mainly due to severe fiber attrition. Glass bubbles breakage occurred after recycling, which diminished its ability to provide lightweighting. Only glass fiber reinforced nylon composites were affected by hygrothermal conditioning, which were characterized as a function of recycling. At saturation point, water absorption for nylon composites was 7.7% by wt. after 45 days of immersion, which significantly affected the mechanical properties. Tensile strength and modulus of glass fiber nylon composites reduced from 88.4 MPa and 5.6 GPa to 36.2 MPa and 1.8 GPa, respectively.