Design of sacrificial network in modified natural rubber leads to strikingly improved mechanical performance with self-healing capability

In this first-of-its-kind report, we present a breakthrough in the field of self-healing rubber for tire applications, aiming to address sustainability concerns and enhance mechanical performance. By leveraging the principles of reversible association of polymer chains with available ionic stickers and the abundant natural resources of natural rubber, we have developed a novel sacrificial network concept that imparts excellent self-healing properties to the natural rubber. In the presence of 1,2-dimethylimidazole, epoxidized natural rubber (ENR) was reacted with various dicarboxylic acids of different chain lengths from two to twelve carbon atoms. It was found that ENR was crosslinked to a considerable extent by this treatment and exhibited remarkable mechanical and dynamic mechanical performance. The long-chain dicarboxylic acid was found to be more effective than its short-chain variant in developing a crosslinked structure. As evidenced by Fourier-transform infrared (FTIR) spectroscopy and electrochemical impedance spectroscopy (EIS) analysis, apart from ester and ether linkages, the crosslinked network structure between the rubber chains was found to be primarily attributed to the formation of ionic groups. Through careful material design and optimization, we have achieved a tensile strength of up to 30 MPa with self-healing capacity of the material meeting the stringent requirements of tire applications. The reversible network structure and its stability were supported by temperature scanning-stress relaxation (TSSR) studies, dynamic mechanical analysis, and Kelvin probe force microscopy studies. By utilizing natural rubber as the base material, our approach contributes to sustainability efforts by reducing the dependence on synthetic polymers and promoting the use of renewable resources.