Efficient degradation and recycling of carbon fiber reinforced epoxy composite wastes under mild conditions by constructing dual dynamic covalent networks

Abstract

The recycling of high-value cores from epoxy composite wastes is critical for environmental protection and sustainable development. However, the efficient degradation of epoxy resin under mild conditions remains a significant challenge due to its stable 3D crosslinked network structure. Herein, we propose an innovative strategy utilizing dual dynamic covalent bonds to achieve efficient, safe, and controlled degradation of epoxy resins in solvents. Specifically, a series of epoxy resins D_xBV_y/NMA containing dual dynamic covalent bonds (imine and ester bonds) were prepared by combining the bio-based epoxy monomer BV-EP, which contains imine bonds, with the commercial epoxy monomer DGEBA, followed by curing with nadic methyl anhydride (NMA). The results demonstrate that the incorporation of BV-EP maintains excellent thermomechanical properties and thermal stability in D_xBV_y/NMA systems. Remarkably, D₅BV₅/NMA achieved 100 % degradation in aminoethanol at 160 °C within just 25 min, indicating an extraordinarily high degradation efficiency. The degradation mechanism was elucidated using FTIR and ¹H NMR, revealing that both imine and ester bonds in the crosslinked structure can undergo exchange reactions with amino groups in aminoethanol. Importantly, the carbon fiber reinforced epoxy composite CF-D₅BV₅/NMA was also efficiently degraded in this system, allowing for recycling through a straightforward post-processing step, yielding virtually non-destructive carbon fibers (CF) and high-purity monomer 9,9-bis(4-aminophenyl)fluorene (BAPF). This work introduces a novel approach for the efficient and lossless recycling of CF from the carbon fiber reinforced epoxy composite wastes, thereby contributing to the sustainable development of the epoxy resin field.