Sustainable castor oil-based vitrimers: Towards new materials with reprocessability, self-healing, degradable and UV-blocking characteristics

Vitrimers with reversible cross-links are emerging promising sustainable materials with reprocessability and recyclability. Here, castor oil-based epoxy resin (EMCO) with epoxy group and carbon-carbon double bonds was prepared through a two-step process and then cured with itaconic acid (IA) through epoxy-acid ring-opening reaction and free radical polymerization to fabricate fully bio-based epoxy vitrimers containing reversible transesterification bond. The thermal-mechanical properties, reprocessability, repairability, and recyclability could be balanced by varying the molar ratio of EMCO to IA. When the carboxyl group/epoxy group molar ratio reached 1.0, the EMCO-IA_1.0 vitrimer exhibited the highest tensile strength of 14.39 MPa and T_g of 52.95 °C. Moreover, the vitrimer can be effectively remodeled (2 h at 180 °C) to prepare films and self-healing thanks to a rapid and mild stress relaxation process (2.56 min at 110 °C) and low activation energy (60.94 kJ·mol⁻¹). More significantly, EMCO-IA vitrimer could be degraded in ethanol solution and recycled to prepare films and also exhibited excellent UV blocking ability. Overall, the EMCO-IA vitrimer can achieve a highly efficient closed-loop recycling without significantly sacrificing the mechanical properties, which can extend the service life and facilitate the sustainable development of the castor oil-based polymeric material.