Lightweight and Strength–Toughness Synergistic Polypropylene Microcellular Composites via Bamboo Fiber/Talc/ EPDM Interface Engineering and Hierarchical Design Under SCF ‐Assisted Injection Molding

ABSTRACT Driven by the urgent demand for automotive lightweighting and low‐carbon manufacturing, it is critical to replace conventional petrochemical foams with polyolefins reinforced by renewable plant fibers. In this study, we developed a hierarchically structured organic–inorganic hybrid microcellular composite by combining dual‐locking interfacial modification with the synergistic nucleation of talc (Talc) and ethylene–propylene–diene rubber (EPDM), integrated into supercritical fluid (SCF) microcellular injection molding. A synergistic design strategy was proposed for the interface, crystallization, and cell morphology of polypropylene (PP) composites. Specifically, alkali treatment combined with maleic anhydride‐grafted polypropylene (MAPP) generated a dual interphase of chemical bonding and mechanical interlocking, markedly improving load transfer between fibers and the PP matrix. Talc platelets and bamboo fibers (BFs) jointly promoted heterogeneous nucleation and enhanced melt strength, while EPDM imparted toughness through a cavitation–shear banding mechanism. When the Talc content was 5 wt% and EPDM 5 wt%, the composite exhibited optimal overall mechanical performance: tensile strength of 34.14 MPa and flexural strength of 51.07 MPa, representing improvements of 71.78% and 33.16% over neat foamed PP. In addition, tensile modulus, flexural modulus, and impact strength were enhanced by 40.26%, 58.21%, and 31.93%, respectively. Meanwhile, the optimized foam exhibited a density of 0.840 g cm −3 , corresponding to a relative density of 0.75 and a weight reduction of approximately 25% compared with its solid counterpart. These enhancements are attributed to the shear‐induced skin–core hierarchical structure, which reconstructs the crack‐tip stress field and enables the integration of lightweight and high mechanical performance without sacrificing processability. This strategy provides both a materials and process pathway for the low‐carbon manufacturing of automotive interior components and establishes a foundation for the engineering application of bio‐based foamed composites.