Orthogonal imine and disulfide exchange in a biobased covalent adaptable network: toward healable and recyclable thermosets

The development of biobased thermosetting materials has garnered considerable interest as a promising alternative to conventional thermosets, which are often constrained by permanent cross-linking and dependence on petroleum-derived feedstocks. Nevertheless, both traditional and bio-based thermosets frequently exhibit limitations in reprocessability and recyclability. In this study, a novel epoxy covalent adaptable network (CAN) incorporating dynamic dual-crosslinking bonds (D-DCB) was synthesized from lignin-derived vanillin (VA) and glycerol propoxylate triglycidyl ether (GPTE). Specifically, a trialdehyde monomer (TAM) was first prepared from VA and GPTE, which subsequently reacted with disulfide-containing compounds (4,4′-diaminodiphenyl disulfide and cystamine) to form bio-based CANs (namely, TAM-APDS and TAM-Cys, respectively). This network synergistically combines imine and disulfide bonds as dynamic covalent units. The imine bonds not only provide fundamental mechanical strength and structural stability but also contribute UV-shielding properties due to their conjugated structure. The disulfide bonds impart reprocessability, self-healing capability, and degradability-enabling rapid disulfide exchange reactions within 1 h using a thiol/ethanol solution at 60 °C. Lap-shear adhesion tests on various substrates demonstrated that the resulting CANs exhibit a high strength of approximately 7 MPa on iron substrates, highlighting their potential as high-performance sustainable adhesives.