Catalyst-free self-healing fully bio-based vitrimers derived from tung oil: Strong mechanical properties, shape memory, and recyclability

Vegetable oil-based vitrimers are innovative renewable polymers that show promising applications. However, their applications are limited by their poor mechanical properties and the need for the use of a catalyst in their preparation. In this study, the renewable tung oil underwent the methyl esterification reaction, Diels-Alder reaction, and epoxidation reaction to obtain TOTGE with terminal epoxy groups. TOTGE was cured with citric acid (CA) to obtain catalyst-free, self-healing, high mechanical strength fully bio-based TOTGE-CA vitrimers. Due to the high reactivity of their terminal epoxy groups, the vitrimer networks have a high density of crosslinks, and thus show good thermal stability and mechanical properties. The curing agent CA introduces a large number of hydroxyl (-OH) groups into the vitrimers and these form abundant hydrogen (H) bonds. The -OH groups in the vitrimers act as a catalyst, allowing topological network rearrangement of the materials in the absence of an external catalyst. Due to their dynamic ester and H bonds, the vitrimers exhibit good self-healing, recyclability, and shape memory properties, making them promising candidates for use as repairable and recyclable adhesives.