Room-temperature closed-loop recyclable high-strength epoxy resin composites based on dynamic boronate ester bonds

Abstract

The permanently crosslinked networks of conventional thermosetting epoxy resins endow glass fiber-reinforced polymer (GFRP) composites with excellent mechanical performance and enable their widespread application in aerospace, automotive, and other fields, but make efficient recycling extremely challenging. In this study, dynamic boronate ester (B-O-C) bonds were introduced as reversible crosslinking units to replace traditional irreversible covalent linkages, enabling the construction of recyclable thermosetting epoxy materials. A concise and effective strategy was developed to construct reversible boronate ester networks within epoxy resins. A hydroxyl-rich linear prepolymer was prepared via aniline-initiated chain extension of bisphenol A-based epoxy resin and was crosslinked with tripropyl borate under catalyst-free conditions, yielding a recyclable epoxy vitrimer (EAT) with high mechanical performance and room-temperature degradability. Owing to the rapid alcoholysis kinetics of B-O-C bonds, the cured EAT thermosets and their GFRP composites could be completely depolymerized in pure methanol within 2 h, enabling clean separation and recovery of the resin and glass fibers. XPS analysis suggested that excess boron-containing groups may react in situ with silanol groups on the glass fiber surface, likely giving rise to Si-O-B interfacial linkages, which may contribute to the excellent mechanical properties of the composites. Reprocessed materials fabricated from recovered resin and fibers retained more than 80% of their original mechanical performance after one recycling cycle. This work provides an efficient and feasible route for achieving closed-loop chemical recycling of high-performance GFRP under mild conditions.