High-performance yet sustainable epoxy composites: from Diels-Alder chemistry to hydrazinolytic degradation

Carbon fiber-reinforced epoxy composites, extensively used in high-performance applications, face significant challenges regarding their recyclability and fire safety. Phosphorus-containing dynamic covalent chemistry offers an effective strategy to address these issues. However, integrating these bonds into either the starting resins or curing agents of epoxy systems typically necessitates complex multi-step syntheses, leading to economic concerns. In this study, we propose a novel one-pot process that simultaneously builds dynamic networks via the phosphonate-containing Diels-Alder (DA) reaction and forms permanent ones via the curing reaction of amine-epoxy system. This innovative approach markedly simplifies the production process, eliminating the need for complex syntheses and additional separation/purification steps, thereby reducing costs and enhancing economic efficiency. The resultant composites exhibit superb flame retardancy, and favorable thermal and mechanical properties. Furthermore, inspired by the Gabriel synthesis, we are the first to employ hydrazinolysis to selectively cleave bonds in DA-based epoxy composite systems, facilitating the recycling of intact carbon fibers alongside the valuable monomers such as maleic hydrazide and 1,6-hexanediamine. This one-pot synthesis strategy represents a substantial step forward in the field of sustainable materials, offering a promising and cost-effective solution for the development of high-performance, recyclable composites.