Bio-based epoxy vitrimers for sustainable thermosets

Vitrimers represent a new field of research because they open new ways of recycling cross-linked polymers, usually not recyclable [1]. In this project we aimed to prepare a bio-based vitrimer based on dynamic chemical reactions between epoxy and acidic groups. The prepared formulations are thermally cross-linked and then reprocessed by a transesterification reaction. The chemicals used for this research are Cardolite® NC-547, a bio-based epoxy monomer synthetized from cardanol oil obtained by the cashew nutshell liquid (Figure 1) [2], and itaconic acid, one of the most important organic acids that can be obtained by biomass. For the cross-linking and transesterification processes two catalysts are used: 2-ethyl-4-methylimidazole and zinc trifluoromethanesulfonate. The first one takes part in the cross-linking reaction between epoxy and acidic groups, while the second one has a role in both cross-linking and transesterification reactions. The use of a double catalyst system is quite innovative for the vitrimer field and allows to optimize the process (Figure 2). The crosslinking reaction is analyzed by using IR-ATR, DSC and gel content measurements: high conversion is obtained with a curing cycle of 2h at 120°C plus 2h at 140°C. The thermal reprocessability of the so-obtained cross-linked polymers is verified by mechanical tests, and the properties of the re-processed vitrimer are compared with those of the virgin material. LCA (life-cycle assessment) analysis is done in order to check the environmental impact of the system.