Carbon Fiber-Reinforced Dynamically Cross-linked Epoxy Resin Composites with Excellent Self-healing and Recycling Performance via Autocatalyzed β-Hydroxyl Ester Bonds

Abstract

Employing epoxy resins containing dynamic covalent bonds to fabricate carbon fiber-reinforced polymer (CFRP) composite materials provides a solution to solve the challenge that traditional epoxy resin composites are difficult to degrade and recycle. The curing reaction between anhydride and epoxy monomer will generate hydroxyl and ester groups, which can undergo transesterification, endowing the epoxy resin with degradation performance. Large amounts of catalysts and an extra alcoholic compound are often required to break down the cross-linked networks for complete degradation, which results in the difficult separation of the degraded product. To solve this dilemma, we synthesized an autocatalytic high-performance recyclable epoxy resin with a tensile strength of 91.9 MPa, Young’s modulus of 2.85 GPa, and a T_g of 91.3 °C. The fully cured epoxy resin can be completely degraded in hot N,N-dimethylformamide due to the fast exchange reaction between the β-hydroxyl and ester bonds autocatalyzed by the formed ternary amine in the network, which may induce loop formation and result in degradation. This fast dynamic exchange reaction also endows the fabricated CFRP composites with a strong interlaminar shear strength of 58.65 MPa and excellent self-healing capacity with a healing efficiency of 99.5%. Moreover, the CFRP composites can also be completely degraded in N,N-dimethylformamide after being heated at 140 °C for 20 min. The recycled fibers can be reused to fabricate new composites with properties comparable to those of the original ones. The degraded product can be recycled into polyurethane with excellent mechanical performance, realizing full recycling of composite materials.