Construction of Hydroxylated Interface Phase on Carbon Fiber Surface and Its Effect on PA6 Composite Performance

Strong carbon fiber/polyamide 6 (CF/PA6) interfacial adhesion is crucial, yet conventional sizing lacks sufficient polar groups. This study develops a novel epoxy-based sizing agent via emulsion technology to address it. Through a rationally designed emulsification process, not only was a highly stable epoxy emulsion achieved, but a flexible cross-linked interfacial layer with high oxygen content (31.5%) and elevated surface energy (79.0 mN·m −1 ) was successfully fabricated on the CF surface. The resulting composites exhibited a 41.0% improvement in tensile strength and a 48.6% increase in interfacial shear strength (IFSS). Furthermore, the compatibilization mechanism of the hydroxyl (  OH) functional groups within the sizing agent was systematically investigated. This work offers a promising pathway for engineering CF surfaces with rich polar functionality and advancing the development of high-performance CF/PA6 composites. Highlights Structure–property relation links sizing agent to interfacial phase. Tuned interfacial  OH content boosts interfacial and mechanical properties. Emulsifier structure controls stability and quality for defect-free composites.