Balancing Mechanical Performance and Repair Ability of Epoxy and Its Composites via Dual Dynamic Mechanism

Introducing dynamic covalent bonds offers a promising strategy to enable the reprocessing and repair of epoxy resins and their composites, with efficacy tied to the type and extent of dynamic exchange. Although combining multiple mechanisms has received increasing attention, in most studies, these multiple mechanisms are independent of each other, lacking more efficient synergistic effects, and often exhibit worse mechanical performance along with elevated reprocessing temperatures. To overcome these challenges, we developed an epoxy vitrimer and its composites incorporating synergistic dual dynamic exchange mechanisms. This was achieved by combining an imine-containing epoxy resin with a curing agent featuring vinylogous urethane (VU) dynamic bonds, which is designed with excess amine groups to undergo dynamic exchange with both mechanisms. The resulting samples exhibit outstanding mechanical properties, including a tensile strength of 100.32 MPa, a glass transition temperature (T_g) of 125.07°C, and an elongation of 6.77%. Reprocessing near T_g allows tensile strength and elongation at break to recover to 75.54% and 52.14% of their original values, respectively, after two cycles. These epoxy vitrimers and composites optimally balance high mechanical strength and structural reversibility through dual dynamic exchange mechanisms. Additionally, this design enables rapid, non-destructive carbon fiber recovery at room temperature and effective shear repair of carbon fiber layers, offering insights for designing longer-lasting epoxy materials and repair strategies.