Controlled Release of Metal Ion Cross-Linkers and Development of Self-Healable Epoxidized Natural Rubber

Chemical cross-linking of rubber is a process to significantly modify the physical properties of the polymer. By this transformation, a highly viscous rubber compound is converted into an elastomer suitable for high-performance products like tires. Conventionally, sulfur or peroxide cross-linking is the preferred mode of vulcanization of the polymer practiced by different rubber industries. To fulfill the growing demand for more durable, high-performance rubber products, the development of self-healing rubber is considered one of the most promising approaches. The present study is an endeavor to mimic self-healing property in commercial epoxidized natural rubber (ENR) utilizing a mechanism that ensures the continuous supply of the healing agent to the affected area. With the advancement of metal coordination as a means of network structure, here, we report for the first time a different method for the preparation of self-healable ENR using mixed metals ions and diamine as cross-linking agents. The availability of a nitrogen coordination site of the diamine along with the reactivity of the oxirane group of epoxidized natural rubber toward metal ions enables the re-establishment of cross-linking sites in a damaged polymer network. A slow release of the metal ions from the metal amine complex to the ultra-active oxirane groups assists this reformation of the network. Additionally, some of the physical properties of the metal ion cross-linked samples are found to be comparable with those of conventional sulfur cross-linked samples.