Reprocessable and recyclable high-performance carbon fiber-reinforced composites enabled by catalyst-free covalent adaptable networks

Carbon fiber-reinforced composites (CFRCs) have been extensively applied in high-tech industry due to their superior mechanical properties. However, the permanent crosslinked networks of thermosetting matrices cause them difficult to reshape, repair and recycle. In this work, we devise a series catalyst-free covalent adaptable networks (CANs) by curing diglycidyl 4,5-epoxycyclohexane-1,2-dicarboxylate (DGEDC) with phthalic anhydride (PA) and glycerol. Benefiting from the rigidity of PA, the resulting DGEDC/PA/Glycerol (DPG) networks possess high mechanical and thermal properties, with glass transition temperature (Tg) of 140–165 °C, thermal degradation temperature (Td5%) of 289–322 °C, fracture strength of 65–78 MPa, and Young’s modulus of 3.2–3.9 GPa. More importantly, the multiple hydroxyl sites endow DPG networks with rapid transesterification reactions (the shortest relaxation time is only 205 s at 180 °C), which allows for material reprocessing, repairing, and degradation. In addition, taking DPG networks as matrix and carbon fibers (CFs) as reinforcement, the obtained DPG/CFs composite exhibits strong mechanical properties (tensile strength and modulus of 559 MPa and 8.5 GPa, bend strength and modulus of 420 MPa and 6.2 GPa) and good welding ability (shear strength of 19 MPa). Furthermore, the composite can be completely degraded in ethylene glycol at 190 °C, achieving efficient and non-destructive recycling of CFs. This research presents an alternative approach for the fabrication of reprocessable and recyclable high-performance CFRCs, which might have broad practical applications in aeronautic engineering and automobile equipment.