Secondary Network Formation in Epoxidized Natural\nRubber with Alternative Curatives

Epoxidized natural\nrubber (ENR) offers a unique combination of\nstrength, sustainability, and versatile structure, making it a good\ncandidate for creating sacrificial and reformable bonds via secondary\ncuratives. These curatives should be simple and compatible with other\nrubber ingredients and industrial mixing processes. Although many\nalternative curatives, including zinc chloride, zinc dimethacrylate\n(ZDMA), and sebacic acid (SA), have been proven to be successful,\nthey have never been compared in the same compound. Moreover, the\neffectiveness of these alternative curatives on network formation,\nincluding their interactions with the other ingredients of a rubber\ncompound, such as fillers, coupling agents, and traditional curatives,\nhas not been fully studied yet. Based on the current study, these\nsecondary curatives alone cannot provide a sufficient level of vulcanization.\nHowever, adding ZDMA or SA together with sulfur curatives allowed\nimproving the tensile properties and showed microlevel self-healing\nbehavior during cyclic loading. The addition of 10 phr (parts per\nhundred rubber) ZnCl<sub>2</sub> created weak, short, and rigid bonds\nin ENR detectable by simple Payne measurements. However, that led\nto active interaction with all compounding ingredients and deterioration\nof the physical properties. Reducing the ZnCl<sub>2</sub> load to\n1 phr allowed full recovery of stress after the cyclic test and fair\ntensile strength of the compound.