Improved interfacial shear strength in carbon fiber/polyamide 6 composite via a novel two‐component waterborne polyurethane sizing agent

Abstract The rise of continuous carbon fiber (CF) reinforced polyamide 6 (PA6) composites has put forward higher requirements for the tailoring of thermoplastic composite interphase. In this work, a novel two‐component waterborne polyurethane (WPU) sizing agent was prepared to improve the interfacial strength of CF/PA6 composite. One of the components was carboxyl terminated polyurethane, the other one was blocked isocyanate. Both of the components were designed to react with the CF surface, as well as the matrix resin during composite fabrication. This sizing agent with excellent storage stability was homogeneously coated on CF surface, introducing abundant reactive groups and improving the CF surface energy remarkably. A linear regression method was applied to determine the interfacial shear strength (IFSS) from the micro‐droplet test. Results showed that the IFSS of the WPU sized CF increased to 51.8 MPa, which was 22% and 47% higher than that of the unsized and epoxy‐compatible sized CF, respectively. That value was also higher than that of the same materials reported in literature. This sizing agent provides a promising method for improving the interfacial strength of thermoplastic composites.