Facile Construction of Zn2+-Carboxyl Salt-Bonding as Sacrificial Unit in EPDM Rubber toward Mechanical and Sealing Resilience Performance Enhancement

In view of the facile reaction between carboxyl groups and zinc oxide (ZnO), Zn²⁺-carboxyl salt-bonding is constructed in ethylene propylene diene monomer (EPDM) rubber system by grafting reaction of glutamic acid (Glu), serving as sacrificial unit endowed EPDM-g-Glu/ZnO sample with excellent reprocessing and recycling ability. Through reaction of ZnO/methacrylic acid (MAA), EPDM-g-Glu/zinc dimethacrylate (ZDMA) composite is further prepared by in situ formation of ZDMA, and ZDMA is rapidly polymerized to form poly-ZDMA (PZDMA) containing massive Zn²⁺-carboxyl ion pairs once vulcanized, which exhibits fuzzy interface with the matrix. Relative to EPDM/ZDMA, the higher polymerization degree of ZDMA is achieved with the reduction of the size of PZDMA clusters, demonstrating the improvement of interfacial bonding, which results in the formation of a developed crosslinking network structure for EPDM-g-Glu/ZDMA. The mechanical strength, fracture toughness, and hysteresis loss of EPDM-g-Glu/ZDMA-40% show a significant increase in comparison with EPDM/CB-40% and EPDM/ZDMA-40%, meanwhile the relatively lower compression set and slower contact stress relaxation are achieved by energy dissipation mechanism of preferential rupture of Zn²⁺-carboxyl salt-bonding before breakage of covalent bonds during compression aging process, revealing the effective enhancement of durable sealing resilience performance.