A reprocessable elastomeric vulcanisate based on Epoxidised Natural Rubber with 50 mol-% epoxide content (ENR-50) was evloved by applying a self-assembled network based on thermochemically exchangeable ester crosslinks to the system. Hydrolysed Maleic Anhydride (HMA) as crosslinking substance in the presence of 1,2-DiMethylImidazole (DMI) as esterification accelerator and Zinc Acetate Dihydrate (ZAD) as transesterification catalyst was employed to generate the exchangeable ester crosslinking system. A sulphur-cured ENR-50 vulcanisate possessing a permanent sulphide crosslinking network was prepared as reference. Based on the results from cure characteristic and chemical structure analyses, the ENR-50 crosslinked with HMA behaves as a dynamic network because of a transesterification reaction catalysed by ZAD, promoting an exchangeable crosslinking network in the system. This dynamic network contributes to an intermolecular rearrangement of the ester crosslinking bonds at elevated temperatures, enabling interfacial self-adhesion and so reprocessability of the vulcanisates. The obtainable vulcanisates can be reprocessed, yielding relatively high retention of mechanical properties compared to their pristine counterpart. The interfacial self-adhesion and reprocessability of the vulcanisates have shown to significantly be improved with a higher loading of ZAD and elevated temperatures. This concept essentially shows a prospect towards developing e.g. novel recyclable and selfhealing systems for elastomers.

The property retentions of silica-reinforced natural rubber vulcanizates with various contents of a self-healing modifier called EMZ, which is based on epoxidized natural rubber (ENR) modified with hydrolyzed maleic anhydride (HMA) as an ester crosslinking agent plus zinc acetate dihydrate (ZAD) as a transesterification catalyst, were investigated. To validate its self-healing efficiency, the molecular-scale damages were introduced to vulcanizates using a tensile stress–strain cyclic test following the Mullins effect concept. The processing characteristics, reinforcing indicators, and physicomechanical and viscoelastic properties of the compounds were evaluated to identify the influences of plausible interactions in the system. Overall results demonstrate that the property retentions are significantly enhanced with increasing EMZ content at elevated treatment temperatures, because the EMZ modifier potentially contributes to reversible linkages leading to the intermolecular reparation of rubber network. Furthermore, a thermally annealing treatment of the damaged vulcanizates at a high temperature, e.g., 120 °C, substantially enhances the property recovery degree, most likely due to an impact of the transesterification reaction of the ester crosslinks adjacent to the molecular damages. This reaction can enable bond interchanges of the ester crosslinks, resulting in the feasibly exchanged positions of the ester crosslinks between the broken rubber molecules and, thus, achievable self-reparation of the damages.

Carbon black-reinforced rubber compounds based on the blends of natural rubber (NR) and butadiene rubber (BR) for tire sidewall applications were formulated to investigate the self-healing efficacy of a modifier called EMZ. This modifier is based on epoxidized natural rubber (ENR) modified with hydrolyzed maleic anhydride (HMA) as the ester crosslinking agent plus zinc acetate dihydrate (ZAD) as the transesterification catalyst. The influence of EMZ modifier content in sidewall compounds on processing characteristics, reinforcement, mechanical and fatigue properties, as well as property retentions, was investigated. Increasing the content of EMZ, the dump temperatures and Mooney viscosities of the compounds slightly increase, attributed to the presence of extra polymer networks and filler–rubber interactions. The bound rubber content and Payne effect show a good correction that essentially supports that the EMZ modifier gives enhanced filler–rubber interaction and reduced filler–filler interaction, reflecting the improved homogeneity of the composites. This is the key contribution to a better flex cracking resistance and a high fatigue-to-failure resistance when utilizing the EMZ modifier. To validate the property retentions, molecular damages were introduced to vulcanizates using a tensile stress–strain cyclic test following the Mullins effect concept. The property retentions are significantly enhanced with increasing EMZ content because the EMZ self-healing modifier provides reversible or dynamic ester linkages that potentially enable a bond-interchange mechanism of the crosslinks, leading to the intermolecular reparation of the rubber network.