Second-Life Thermoset Manufacturing via Mild Solvolysis of Epoxy-Matrix Composites and Wet-Laid Mat Production

The growing use of carbon fiber–reinforced thermosets has led to the accumulation of significant composite waste, posing environmental and economic challenges, and threatening the long-term sustainability of these high-performance materials. In line with circular economy principles, this study explores a closed-loop strategy for high-fidelity carbon fiber recovery from fully cured pultruded epoxy–anhydride composites using a mild, low-temperature solvolysis process. The reclaimed fibers were subsequently reprocessed by wet-laid into nonwoven mats and used to fabricate second-life epoxy composites, which were benchmarked against analogous systems based on virgin carbon fibers. Single fiber tensile strength was retained after solvolysis, while the apparent interfacial shear strength with the epoxy matrix decreased by approximately 20%, attributed to partial sizing removal and fiber surface modification. Despite this reduction in interfacial strength, reclaimed-fiber composites exhibited mechanical performance close to their virgin-fiber counterparts, with a flexural strength of approximately 384 MPa, only 4% lower than that of the virgin-fiber composite that has a slightly higher fiber volume percentage. Thermal and dynamic-mechanical analyses revealed the same thermal degradation behavior and glass transition temperatures for both composite types. These findings demonstrate that the combined mild solvolysis and wet-laid processing route have the potential to become a scalable and industrially viable alternative to conventional high-temperature or aggressive chemical recycling methods, enabling the effective conversion of thermoset composite waste into valuable secondary raw materials and advancing circularity in the composites industry.