Controlled Release of Metal Ion Cross-Linkers and Development of Self-Healable Epoxidized Natural Rubber
Subhradeep Mandal, Frank Simon, Shib Shankar Banerjee, Lewis B. Tunnicliffe, Charoen Nakason, Chayan Das, Mithun Das, Kinsuk Naskar, Sven Wießner, Gert Heinrich, Amit Das
Abstract
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.