Fabrication of Highly‐Filled Waste <scp>PET</scp> Fiber/ <scp>PE</scp> Composites With Superior Fiber Length Retention and Enhanced Properties Using Short Mixing‐Section Elliptical Rotors in a Twin‐Rotor Continuous Mixer

ABSTRACT Research on fiber‐reinforced polymer composites has yielded significant achievements. However, with the continuous advancement of research and expansion of application fields, there is an urgent need to enhance the fiber loading capacity and improve fiber length retention in composites to further optimize material performance. In this study, the effects of rotor configuration and rotational speeds on the structure and properties of waste polyethylene terephthalate (PET) fiber/polyethylene (PE) composites in a twin‐rotor continuous mixing system were systematically evaluated. The rotor configurations included a long mixing section triangular cross‐section rotor ( R T ), a long mixing section elliptical cross‐section rotor ( R E ), and a short mixing section elliptical cross‐section rotor ( R S ). Notably, the fiber mass content in the composite materials can reach as high as 50%, which highlights the system's strong mixing capability. The results show that at the same rotational speed, fiber length retention follows the order R T &lt; R E &lt; R S , demonstrating an inverse correlation with shear strength, which follows the order R T &gt; R E &gt; R S . The optimized low‐shear design of the R S rotor exhibits the best comprehensive properties. Compared with the R T rotor with a rotational speed of 100 rpm, the tensile strength of the sample prepared using the R S rotor shows an enhancement of 25.4%, the flexural strength an improvement of 27.9%, and the impact strength an increase of 11.8%. In addition, the optimized low‐shear design of the RS rotor enables the production of composites with stable performance across a wide processing window. This study preliminarily explores the structure–property relationship between rotor configuration, fiber length preservation, and material properties. Overall, this capability provides both theoretical guidance and technical support for the high‐value recycling of waste textiles and, consequently, promotes the industrial‐scale production of fiber‐reinforced composites.