Unveiling Interface Evolution: Degradation‐Induced Changes in Polypropylene/Calcium Carbonate Composites Upon Repeated Reprocessing

Establishing a high‐value circular economy for plastics is paramount for sustainable development. While recycling high‐load calcium carbonate (CaCO 3 )/polypropylene (PP) composites is critical, the evolution of the polymer‐filler interface during reprocessing, which governs performance, is poorly understood. This study investigates the microstructural evolution, particularly at the interface, of a high‐fill (65 wt%) PP/CaCO 3 composite subjected to 1, 3, and 5 (P1, P3, P5) melt‐reprocessing cycles. A suite of characterization techniques (GPC, MFR, FTIR‐Rheometry, SEM, TG‐DSC, XRD) was employed. Results demonstrate that PP matrix degradation, characterized by significant chain scission (confirmed by GPC and MFR) and thermo‐oxidation (confirmed by FTIR), is the primary event. This matrix degradation, in turn, dictates the interfacial behavior. SEM imaging directly revealed a transition from a well‐bonded interface in P1 to progressive interfacial debonding and filler agglomeration in P3 and P5. This study reveals that the degradation of the polymer matrix, which subsequently compromises interfacial integrity, is the root cause of performance deterioration. Consequently, strategies for improving the recyclability of these composites must prioritize stabilizing the polymer matrix to preserve interfacial integrity.