Efficient reclamation of carbon fibers from epoxy composite waste through catalytic pyrolysis in molten ZnCl2

Abstract

Carbon fiber-reinforced polymer composites have been widely used in various fields and have inevitably produced large amounts of composite waste. The recycling of carbon fibers with high value has become an active research topic at related institutions and production enterprises. In this paper, the catalytic pyrolysis of T700 carbon fiber/epoxy composites in molten salt was studied. Due to the efficient solubility of molten ZnCl₂ for the epoxy matrix and catalytic fracture of the C–N bonds by the action of Zn²⁺ ions, the epoxy composites can be completely degraded at 360 °C in 80 min under standard pressure, and the reclamation efficiency was significantly enhanced compared with conventional pyrolysis reclamation without a catalyst. The types and contents of the main oxygen-containing functional groups on the surfaces of the fibers reclaimed with ZnCl₂ were similar to those of the virgin fibers, and the graphitization structure of the carbon fibers was not destroyed in the pyrolysis process. The tensile strength of a monofilament of the fibers reclaimed with ZnCl₂ was obviously higher than that of fibers reclaimed in air; it reached a high retention rate that was about 95% that of the virgin fibers. The fibers reclaimed with ZnCl₂ after sizing exhibited a desirable reinforcing effect on the flexure performance and interlaminar shear strength of unidirectional carbon fiber/epoxy composites which was close to the performance levels of composite samples containing commercial T700 carbon fibers. Therefore, efficient technology to reclaim high-quality carbon fibers from epoxy matrices has been devised.