Processability of End‐of‐Life Vehicle‐Derived Recycled Polypropylene–Glass Fiber Composites in Material Extrusion: Heterophase Blend Structure and Dimensional Stability

ABSTRACT Recycled polypropylene (rPP) composites recovered from end‐of‐life vehicles (ELVs) are expected to serve as additive manufacturing feedstocks; however, systematic characterization data on these materials remain limited. In this study, ELV‐derived rPP and glass fiber reinforced recycled polypropylene (rPP‐GF) composites obtained from two different recycling sources were characterized through thermal, rheological, morphological, and mechanical analyses, and their processability was evaluated via fused filament fabrication (FFF) and fused granular fabrication (FGF). DSC analysis revealed dual melting peaks at 126°C and 161°C, confirming a heterophase blend structure (PP/POE or PP/EPDM) characteristic of automotive bumper materials. This structure reduces the crystallizable fraction of PP, contributing to the suppression of crystallization‐induced shrinkage. TGA, rheometry, SEM fractography, and fiber length analysis further revealed source‐dependent variations in GF content, viscoelastic behavior, interfacial bonding quality, and fiber damage. FFF specimens printed on a laser‐textured build plate to enhance bed adhesion exhibited tensile strengths of 22–29 MPa with warpage of 0.34%–0.41%, substantially lower than that of commercial virgin PP‐GF30 (1.4%), attributed to the heterophase structure and shrinkage‐constraining effect of GFs. FGF‐processed rPP‐GF30 achieved a longitudinal tensile strength of 49.08 MPa and an elastic modulus of 3.84 GPa. This study provides systematic characterization data on ELV‐derived rPP composites, serving as a baseline reference for recycled PP composites in material extrusion additive manufacturing.