Waterborne Epoxy Sizing Agent of CF / EP Composites: Improving the Interfacial Properties and UV ‐Resistance Properties

The interfacial adhesion between carbon fiber (CF) and epoxy resin (EP) has a significant impact on the mechanical properties of carbon fiber reinforced epoxy resin (CFRE) composites. In this work, the terminal carboxyl hydrophilic polymer was prepared by esterification reaction between anhydride and hydroxyl, then the epoxy resin E51 was grafted with the terminal carboxyl hydrophilic polymer to synthesize the hydrophilic resin (UV‐WEP) of the sizing agent. The mechanical properties of the CF sized with sizing agent (UV‐WEP‐2.0) exhibited excellent enhancement effect, with the values of the interlaminar shear strength (ILSS) of CFRE composites increased to 99.66 MPa, compared with unsized CFRE composites, which had an increment of 40.9% (70.69 MPa). The interfacial shear strength (IFSS) was significantly boosted to 56.09 MPa compared to unsized CF, and the interface effect strength increased by 40.8%. The results of anti‐ultraviolet performance research showed that the mechanical strength retention rate (MSR) of CFRE composites remained about 95% after 7 days irradiated under ultraviolet aging lamps (wavelengths of 313 and 340 nm). The employment of the UV‐WEP sizing agent is able to effectively upgrade the interfacial adhesion between CF surface and the matrix resin, and expand the application field of CFRE composites.