A comparison of mechanical properties of recycled high-density polyethylene/waste carbon fiber via injection molding and 3D printing

Recycled high-density polyethylene (r-HDPE) was combined with waste carbon fiber by loading 6 k, 12 k, and 24 k tows through an extruder to create thermoplastic/carbon pellets with fiber volume fractions of 11.2%, 18.9%, and 29.5%, respectively. Tensile and flexural coupons were subsequently produced via injection molding and novel 3D printing. The addition of carbon into r-HDPE in all cases showed increased mechanical properties. Maximum increases were observed through the inclusion of 29.5% fiber volume fraction. Increases in tensile and flexural modulus of up to 2.9 GPa (+505.9%) and 5.8 GPa (+711.0%) respectively were observed for r-HDPE/carbon fiber (CF) samples. Increases in tensile and flexural strengths of up to 57.9 MPa (+311.8%) and 47.7 MPa (+188.0%) respectively were observed for 29.5% r-HDPE/CF samples. Some variance in mechanical performance between injection molded and 3D printed samples was observed indicating production methodology might influence final material performance.