Biodegradable-Renewable Vitrimer Fabrication by Epoxidized Natural Rubber and Oxidized Starch with Robust Ductility and Elastic Recovery

Facilitating biobased epoxidized natural rubber (ENR) vitrimer with biodegradable-renewables and reprocessability is a facile strategy to reduce environmental pollution and the carbon emission evoked by waste vulcanized rubber. Herein, oxidized starch with 57% carboxyl content (OST-57) was fabricated by H2O2/Cu2+ oxidation and served as a bio-macromolecular cross-linking agent. When OST and ENR latex were mixed and subjected to thermal processing, the beta-hydroxyl ester bonds between OST-57 and ENR were formed and covalent topology networks were constructed. Consequently, the cross-linking density dominated the comprehensive performance of this novel biobased ENR vitrimer, and enabled it to achieve a high elongation at break (1108%), elastic recovery (90%), shape fixed ratio (99.5%), and shape recovery ratio (95.6%) when the content of OST-57 was 30 phr. Meanwhile, due to the low activation energy (E-a) (80.3 kJ/mol) of transesterification, the ENR/OST-57 vitrimer exhibited sound thermo-activated reprocessability, and its loss in mechanical properties was lower than 12% even after being subjected to thermal reprocessing twice. Noteworthily, different from those of the presented vitrimer, ENR/OST-57 showed a distinctive biodegradable-renewable feature when alpha-amylase was adopted and destroyed the cross-linking network. As a result, the biodegradable ENR with residual beta-hydroxyl ester bonds presented similar features as the neat ENR when diisopropylbenzene peroxide was utilized to form the chemical bond cross-linking topology networks. This novel strategy of fabricating biobased vitrimer will promote ENR for wide applications in the field of high ductility and recovery without environmental impact.