Optimizing electrochemical strategy from single to mixed electrolytes for enhanced carbon fiber-epoxy interfacial performance

To enhance the interfacial bonding between carbon fiber (CF) and epoxy resin (EP), this study employed electrochemical oxidation to modify the CF surface. Electrochemical oxidation of CFs was conducted using phosphoric acid (H 3 PO 4 ), ammonium dihydrogen phosphate (NH 4 H 2 PO 4 ), and a 1:1 mixed electrolyte, followed by systematic evaluation of their impacts on surface morphology, microstructure, chemical composition, tensile strength, and interfacial shear strength (IFSS). The results showed that H 3 PO 4 treatment led to significant etching and an increase in active functional groups but caused greater fiber strength loss. In contrast, NH 4 H 2 PO 4 treatment resulted in milder etching, less strength degradation, and the introduction of C-N functional groups, yielding higher IFSS compared to H 3 PO 4 -treated CFs. The mixed electrolyte achieved an optimal balance, combining effective surface modification with better strength retention. The IFSS of CFs treated with the mixed electrolyte increased to 60.20 MPa-a 55% improvement over the unmodified system-attributed to enhanced physical and chemical interactions at the interface. This work demonstrates a promising electrochemical oxidation strategy for surface modification of fibers, holding considerable potential for applications in advanced composite materials.