Reprocessable carbon fiber composites via disulfide-exchange epoxy vitrimers: experimental and molecular simulation insights

Abstract

The growing demand for carbon fiber-reinforced polymer (CFRP) composites in high-performance sectors such as wind energy and automotive underscores the urgent need for recyclable alternatives to traditional thermoset systems. Although disulfide-based epoxy vitrimers have shown promise for reprocessability, a clear correlation between dynamic bond exchange kinetics, network structure, and composite-level mechanical performance remains insufficiently understood. In this study, we present reprocessable and recyclable carbon fiber composites enabled by epoxy vitrimers dynamically crosslinked with 2,2′-dithiodibenzoic acid (DTBA). Among the tested formulations, the vitrimer with 2 wt% DTBA (EPD-2) exhibited optimal performance, combining high thermal stability (T_d5% = 396 °C), accelerated stress relaxation, and high self-healing efficiency (91%), indicating a balanced crosslink density and network mobility. Using vacuum-assisted resin infusion molding (VARIM), this EPD-2 matrix was integrated into carbon fiber composites (EPD-2-CF), which demonstrated high tensile strength (290 MPa), thermoformability, and shape recovery. The composites could be chemically degraded under controlled solvent-assisted conditions, enabling recovery of intact carbon fibers while preserving their structural integrity and enabling closed-loop fiber reclamation. Molecular dynamics (MD) simulations provided molecular-level validation of the composite mechanical response, with the simulated Young's modulus (2.74 GPa) in closely matching experimental results (2.69 GPa). Temperature-dependent creep simulations qualitatively reproduced experimental trends, revealing increased strain and delayed recovery from 130 °C to 170 °C due to activation of disulfide exchange mechanisms. This study establishes a vitrimer composite platform that correlates dynamic network design with composite viscoelastic behavior, advancing the development of recyclable high-performance CFRPS.