Investigating\nthe Crucial Role of 1,2-Dimethyl Imidazole\nin Developing Ferric-Mediated Recyclable XNBR Composites

To resolve the trade-off between permanent cross-linking\nand recycling,\nthe integration of dynamic metal-ligand coordination bonds into elastomer\nsystems is a burning topic of current research. This approach could\nprovide recyclable elastomeric materials that are otherwise not possible\nwith conventionally cross-linked elastomers. Therefore, proper utilization\nof such a dynamic bond could significantly contribute to sustainability\nas well as promote the principles of a circular economy. In this work,\nwe utilized a heterocyclic imidazole base (1,2-dimethyl imidazole,\nDMI) to achieve controlled cross-linking of carboxylated nitrile butadiene\nrubber (XNBR) via ferric-carboxylate interaction. This was investigated\nand confirmed by X-ray photoelectron and infrared spectroscopy. This\nis further supported by swelling and rheological studies. The resulting\ncomposites show multistep recyclability without any further deterioration\nof mechanical performance. Even after the third recycling, the DMI\ncontaining composites XNBR-DMI<sub>1</sub>-Fe<sub>1.5</sub> and XNBR-DMI<sub>4</sub>-Fe<sub>1.5</sub> demonstrate recycling efficiencies as high\nas 84 % and 90 %, respectively. This is well-supported in the creep\nstudy, where the deformation recovery for those composites at 130\n°C was found to be 53.4 % and 65.2 %, respectively. The development\nof such an excellent recyclable and ecofriendly elastomer material\nbecomes possible via the dynamic coordination network of the ferric\nion complex throughout the XNBR matrix. Furthermore, the formation\nof clusters, as evidenced by the small-angle X-ray scattering study,\nis believed to enhance the mechanical properties. A plausible mechanism\nis proposed that shows the critical role of DMI in the cross-linking\nprocess.