Elastomer-Mediated Interparticle Coupling Promotes Low-Threshold Rheological Network Formation in EPDM-g-MA-Compatibilized PP/Talc Composites

Conventional compatibilization of polypropylene (PP)/mineral composites primarily improves local filler–matrix adhesion and dispersion. This study provides evidence for an elastomer-mediated interparticle bridging mechanism in which maleic anhydride-grafted ethylene propylene diene monomer (EPDM-g-MA) extends talc-associated polymer regions and promotes long-range elastic connectivity between neighboring platelets. Composites containing 5–40 wt% talc and 2.5–20 wt% EPDM-g-MA were characterized by frequency sweep, stress relaxation, strain sweep, and scanning electron microscopy. PP-g-MA and hybrid PP-g-MA/EPDM systems served as controls to distinguish conventional MA-mediated adhesion, independent elastomer addition, and their integration within EPDM-g-MA. PP-g-MA improved local interfacial continuity without promoting early network formation, whereas the hybrid systems failed to reproduce the low-threshold response of EPDM-g-MA. The apparent rheological network threshold decreased from approximately 40 wt% talc in the uncompatibilized system to approximately 30 wt% at 2.5–5 wt% EPDM-g-MA, 20 wt% at 10 wt%, and ≤5 wt% at 20 wt%. Effective interaction-volume analysis provides a geometric basis for the observed threshold reduction, while the combined rheological and morphological results support the development of talc-associated polymer regions into stress-bearing elastomer-mediated coupling. These findings establish compatibilizer architecture as a powerful strategy for controlling low-threshold melt-state network formation in PP/talc composites.