High-performance and fully recyclable epoxy resins cured by imine-containing hardeners derived from vanillin and syringaldehyde

Increasing concerns about environmental protection have driven the rapid development of recyclable and sustainable thermosetting polymers. Herein, two biobased epoxy hardeners containing imine bonds were prepared from lignin-derived aromatic aldehydes (vanillin and syringaldehyde). The epoxy resins cured by these two hardeners showed comparable mechanical performances in comparison to traditional epoxy resins. Owing to the dynamic feature of incorporated imine bonds, both cured epoxy resins could be repeatedly reprocessed via hot pressing like thermoplastics, and were degradable in the amine solution. It is noteworthy that a closed-cycle chemical recycling process could be realized by utilizing the degradation products to prepare fresh epoxy resins. Notably, the flexural strength and modulus of the chemically recycled and thermally reprocessed epoxy resins were nearly 100% recovered. In addition, both cured epoxy resins showed acceptable glass-transition temperature, thermal stability and chemical resistance. Taken together, our work offered a simple method to develop biobased epoxy resins with versatile recyclability and high performance recovery rates.