L-Cysteine-Encapsulated MXene Nanosheet Possessing Ultra-Antioxidation in Aqueous Suspension for Electrophoretic Deposition Assisted Carbon-Fiber-Surface Modification

With recent progress in 2D materials, Ti 3 C 2 T x MXene featured high metallic electrical conductivity, high electromagnetic interference shielding effectiveness, and super in-plane stiffness, exhibits unique advantages in many fields, but is rarely applied as a sizing agent in long-time continuous processing of carbon fiber sizing because of its poor ambient stability in aqueous suspension. Herein, a new strategy to chemically encapsulate the reactive sites of MXene nanosheet with l -cysteine for restricting the attacking of water and/or oxygen in aqueous suspension is proposed. Based on the ultra-antioxidation, polarity, and electrical properties of l -cysteine-encapsulated Ti 3 C 2 T x MXene (LC-MX) nanosheet, the LC-MX, even if aging for weeks in aqueous suspension, can be deposited on the surface of high-modulus carbon fiber (HMCF) uniformly via the electrophoretic deposition assisted sizing. Benefiting from the enhanced surface energy, wettability, and roughness of LC-MX-sized HMCF (HMCF-LCMX) relative to that of unsized one (U-HMCF), the interfacial property of HMCF-LCMX/epoxy (EP) composites is also improved, for which the interlayer shear strength (ILSS) of the composite reached 88.5 MPa, 52.8% higher than that of U-HMCF/EP composite (57.9 MPa). This work makes an essential step toward the application of ultra-stable MXene nanosheet suspension in large-scale continuous carbon fiber sizing.