Strong and recyclable soybean oil-based epoxy adhesives based on dynamic borate

Biobased and recyclable epoxy vitrimer adhesives (ESOBV) containing dynamic borate ester bonds were formulated from epoxidized soybean oil (ESO) and a dithiol borate ester curing agent (BDB) via a thermally-induced “thiol-epoxy” click reaction. The cross-linked ESOBV adhesives showed superior adhesion strength (3.84–9.61 MPa) on various substrates including steel, glass, wood, and bamboo plates. The reaction between the epoxy groups from ESO and the sulfhydryl groups from BDB generates a large number of hydroxyl groups, which could form hydrogen bonds with substrates. The cured ESOBV adhesives had high tensile strength (18.74–25.14 MPa) and superior thermal stability. The dynamic borate ester bonds in the network undergo topological rearrangement at evaluated temperature, enabling the ESOBV good reprocessability and reusability. The adhesives could be recycled via molecular rearrangement, and the recycled solid ESOBV had comparable lap-shear strength on substrates to the original liquid ESOBV. This study provides a simple method for preparing strong and recyclable vegetable oil-based adhesives.