Comparative study on the mechanical behaviors of compression molded, additively manufactured, and injection molded recycled carbon fiber reinforced rHDPE composites

Adding fibers into recycled plastics and converting them into composites have drawn significant attention because of improved strength and modulus for the recycled plastic. This work focuses on developing recycled carbon fiber (rCF) reinforced recycled high-density polyethylene (rHDPE) composites using three common processing methods and comparably studying their mechanical behaviors. Compression molding (CM), additive manufacturing (AM), and injection molding (IM) were used to produce rCF/rHDPE composite samples with different fiber contents (10 wt% and 20 wt%) for tensile testing and thermal characterization. The mechanical performance varied significantly among composite samples from different processes. Tensile strength and modulus increased with higher rCF content in all samples. Adding 10% rCF led to tensile strength increases of 11.2%, 15.2%, and 72.1% for CM, AM, and IM samples, respectively, compared to neat samples. Doubling the fiber content to 20% rCF resulted in further enhancements of 29.3%, 58.2%, and 91.4%. Fiber alignment notably influenced tensile modulus, while void content had a greater impact on tensile strength. A combination of ductile and brittle fracture modes were found in both CM and IM samples. These findings emphasize the critical role of manufacturing processes and material composition in determining composite performance.