Preparation of self-healing EPDM/ionomer thermoplastic vulcanizates with ionic network for automotive application: Effects of maleic anhydride grafted EPDM as compatibilizer

Abstract

This work evaluates the effects of maleic anhydride grafted ethylene-propylene-diene rubber (EPDM-g-MAH) on the processing characteristics, compatibility and mechanical properties of EPDM/Ionomer blends. Dynamic vulcanization process was used to fabricate thermoplastic vulcanizates (TPVs) of different compositions using EPDM polymers and high acid (HA60D) or mid acid (MA60D) containing thermoplastic ionomers. The addition of EPDM-g-MAH in EPDM/Ionomer blends had a predominant role as a compatibilizing agent, which affected the processability and properties of the final material. The tensile properties showed significant improvement with increasing the content of compatibilizer in the vulcanizates. The microscopical analysis of fracture surfaces further supported the heterogeneous nature of the blends and compatibility of the polymer phases. The concept was based on a simple ionic crosslinking reaction between carboxyl groups present in the ionomer and zinc oxide (ZnO), where the formation of reversible Zn2+covalent crosslinks exhibits the self-healing behavior. The combination of blending and ionic cross-linking improved not only mechanical properties but also improved self-healing performance. The self-healing nature of the TPVs has been identified by scratch resistance test, where the ternary blends (EPDM/Ionomer/EPDM-g-MAH) showed 100% healing efficiency of the scratch surface at 89°C for 24 h.