Improving the Toughness of Recycled <scp>PET</scp> / <scp>HDPE</scp> Through Mixed Screws to Achieve High‐Performance <scp>3D</scp> Printing

ABSTRACT To improve the performance of mechanically recycled polyethylene terephthalate (PET)/highdensity polyethylene (HDPE) blends, it is necessary to reduce the number of melt cycles and enhance dispersive‐mixing efficiency. This study developed a mixing‐screw 3D printer (MSP) integrating an extensional‐flow‐field mixing element to enable one‐stop processing and modification, with a conventional single screw 3D printer (CSP) serving as a control. Through numerical simulations and 3D‐printing experiments, this study systematically investigated the effects of screw configuration and composition ratio on the performance of recycled PET/HDPE blends. The results showed that MS outperformed CS in pressure‐buildup capability, velocity distribution, and residence time characteristics, thereby improving the uniformity and degree of dispersion of the dispersed phase. Under identical composition ratios, MSP achieved better dispersion of the reinforcing phase within the matrix, resulting in enhanced mechanical properties relative to CSP, and the tensile‐fracture surfaces exhibited more pronounced microfibers. This study provides a theoretical basis for simplifying plastic recycling processes and improving the utilization of recycled materials.