Recyclable and Self-Healing Natural Rubber Vitrimers from Anhydride-Epoxy Exchangeable Covalent Bonds

Dynamic covalent networks (DCNs) contain exchangeable covalent bonds that can undergo dynamic structural changes under external stimuli. Employment of DCNs in elastomers instead of static cross-links provides a pathway for designing reprocessable and recyclable rubbers. Vitrimers are examples of DCNs that utilize associative covalent bond-exchanging chemistry to keep the total number of cross-links constant, making them recyclable, reprocessable, and self-healing. This study primarily investigated the design of a natural rubber (NR) vitrimer via anhydride-epoxy dynamic cross-linking using a scalable process and benign reagents, such as maleic anhydride (MA) or bisphenol A diglycidyl ether (DGEBA), which can be reprocessed and self-heal with heat stimuli. Reactive melt mixing was employed to synthesize the vitrimers, and the reaction success was confirmed by using various chemical analysis approaches. The rubber vitrimer possesses a high activation energy (139.7 kJ/mol) and low freezing topology temperature (65 degrees C), demonstrating a robust exchange network. The NR vitrimers could undergo multiple rounds of reprocessing, unlike peroxide- or sulfur-cured NR, due to their robust dynamical cross-linking networks generated by the adaptable covalent bonds. Moreover, the NR vitrimers exhibited unprecedented self-healing capabilities to maintain their original mechanical characteristics. The recyclability of NR is a significant achievement in reducing post-consumer rubber waste and virgin material utilization. The self-healing functionality is also appealing in applications that require on-site assembly or repair as well as to help increase the lifespan of the elastomers.