Fully bio-sourced catalyst-free covalent adaptable networks from epoxidized soybean oil and L-tartaric acid

Epoxidized vegetable oil (EVO)-based epoxy systems offer a promising avenue for replacing non-recyclable petroleum-based thermoset elastomers. Looking towards future prospects, they also hold potential to evolve into sustainable covalent adaptable networks (CANs). Typically, transesterification-based CANs require catalysts to achieve crosslinked structures that are reprocessable at relatively high temperatures (T ≥ 150 °C). In this study, epoxidized soybean oil (ESBO) was cross-linked with a eutectic hardener composed of L-tartaric acid (TAR) and ethyl lactate (in an aqueous solution), resulting in the development of a fully bio-based 3D covalent network capable of reprocessing without the need for an exogenous catalyst. In addition, it was demonstrated that the peculiar structure of L-tartaric acid, with –OH groups linked to its backbone, plays a prominent role in the reactivity of the system. These free hydroxyl functions facilitate both the ring-opening of epoxides and transesterification reactions, thus enhancing both curing and covalent exchange kinetics.