Constructing robust C–N bonding interphases of carbon fiber/epoxy composites via the electrode-switching electrochemical surface treatment of carbon fibers

The interphase formed between carbon fiber (CF) and polymer matrix is crucial to improve the mechanical properties of carbon fiber reinforced polymer (CFRP) composites. Various surface treatment methods have been developed for grafting functionalized molecules on the CF surface to form robust covalent bonding interphase. However, the state-of-the-art strategies demand long reaction time, complex operation and harsh reaction conditions, which cannot meet growing demands for large-scale actual production. Herein, an electrode-switching electrochemical surface treatment (ESET) method was proposed for the efficient and controllable grafting of ethylenediamine (EDA) molecules on the CF surface within merely 180 s. The obtained o-r-CF@EDA was successively used as the anode and cathode for grafting EDA molecules on the surface. It exhibited a high surface N content of 18.74 at.% (with a maximum of 32.04 at.%) and surface energy of 52.61 mN m⁻¹. When combined with epoxy resin (EP) matrix, the average interfacial thickness of o-r-CF@EDA/EP composite reached 495.6 nm, resulting in an expected interlaminar shear strength (ILSS) of 126.5 MPa. Moreover, the reaction mechanism of ESET method and covalent C–N bonds enhancing the interfacial interaction were discussed in-depth. This work presents promising strategy for grafting targeted molecules onto the CF surface and developing high-performance CFRP composites.