Biobased and Reprocessable Vitrimers Based on Cardanol-Derived Epoxy for More Sustainable Thermosets

Abstract

Vitrimers, permanently cross-linked polymers with dynamic covalent bonds that allow the network to change its topology, represent an intriguing field of research as they open new ways of recycling cross-linked polymers that are usually not recyclable. The aim of this work is to prepare an innovative biobased vitrimer starting from the reaction between epoxy and acidic groups. The formulations are thermally cross-linked and then reprocessed by a transesterification reaction. The chemicals used are Cardolite NC-547, a biobased epoxy monomer synthesized from cardanol oil, and itaconic acid. Two catalysts are used: 2-ethyl-4-methylimidazole and zinc triflate. The first one mainly takes part in the cross-linking reaction, while the second one plays a role in both cross-linking and transesterification reactions. A conversion of 86% and a gel content of 82–84% are obtained when both catalysts are used. The thermal reprocessability of the cross-linked polymers is verified by mechanical tests, and the properties of the reprocessed vitrimers are compared with those of the virgin materials. Results show that a good reprocessability is obtained, with no significant change in conversion and gel content values, when a proper amount of zinc triflate is used. A slight increase in cross-linking density values and mechanical properties is observed after reprocessing. A preliminary life cycle assessment (LCA) is performed with the aim of guiding research with relevant environmental information. LCA results suggest that biobased vitrimers could lead to the production of more sustainable products compared to fossil-based ones.