Reinforcement of carbon fibers: γ-irradiation induced microporous modulation and surface defect repairing with graphene quantum dots

Abstract Due to the presence of numerous defects both internally and on the surface, carbon fiber exhibits mechanical properties far below theoretical predictions. Finding a rapid and effective method for reinforcing the matrix remains a challenge. To address this, we have conducted structural reinforcement of carbon fiber by improving the orientation of internal micropores and eliminating surface defects. On the one hand, we subjected the carbon fiber to a dose of 100 kGy of gamma-ray irradiation in the air. After testing, the mechanical properties of the carbon fiber improved by 5.59%. Analysis using techniques such as small-angle x-ray scattering revealed that gamma rays can slightly alter the orientation of the fiber’s internal micropores and enhance graphitization to some extent. On the other hand, we introduced graphene quantum dots (GQDs) onto the surface of the carbon fiber using electrostatic spraying and electrophoretic deposition techniques to fill the defect sites. Compared to untreated carbon fiber, the mechanical properties improved by 10.65% and 9.40% when GQDs were grafted using electrophoretic deposition and electrostatic spraying methods, respectively. This improvement can be attributed to the adsorption of GQDs on the surface of the carbon fiber, which disperses stress during tensile loading and delays fracture. Finally, grafting of GQDs onto the surface of gamma-irradiated carbon fibers by electrophoresis improved the mechanical properties of the carbon fibers by 15.53% compared to unmodified carbon fibers. This work provides a more comprehensive perspective for repairing carbon fiber structures.