Strength, repairability, and debonding of vitrimer structural adhesive joints

Introduction: Debondable and repairable epoxy-based vitrimer adhesives offer a sustainable solution to conventional epoxy adhesives for structural applications. This study evaluated the performance of a vitrimer adhesive in structural single-lap-bonded joints and investigated its repairability and debonding characteristics in comparison with those of a conventional epoxy adhesive. Materials and methods: Metal substrates, aluminum (Al6061) and stainless steel (SS303), were used to fabricate similar and dissimilar single-lap-bonded joints with vitrimer and conventional epoxy adhesives. Lap shear strength (LSS) testing was conducted to evaluate the mechanical performance. The debonding behavior was examined using a mixed solvent system of dimethylformamide (DMF) and ethylene glycol (EG) at different temperatures. Repairability was evaluated through repeated repair cycles, and the retained properties were investigated. Results: Results revealed that the vitrimer-bonded joints exhibited a maximum lap shear strength of 8.8 MPa. A mixed cohesive–adhesive failure mode was observed in the vitrimer-bonded joints for both similar and dissimilar substrate-bonded joints. The repaired vitrimer adhesive-bonded joints retained 89%, 82%, and 67% of their original lap shear strength after the first, second, and third repair cycles, respectively. Elevated temperatures significantly accelerated the debonding process, with complete debonding achieved within 90 min at 150 °C, whereas debonding required 5–6 h at 80 °C and approximately 36 h under ambient conditions. Conclusions: The results demonstrate the successful repair of vitrimer adhesive-bonded joints up to the second cycle with 82% retained properties, and easy debonding makes them a promising candidate for applications in sustainable structural adhesives.