Interfacial amide functionalization induces transcrystallization and enhances mechanical properties in carbon fiber/polyamide 6 composites

Poor interfacial adhesion limits the performance of carbon fiber/polyamide 6 (CF/PA6) composites. Here, we develop an epoxy-based sizing agent with amide-functional emulsifiers to construct a cross-linked interphase with tunable amide content on CF surfaces. This interphase enhances surface energy and wettability, promoting hydrogen bonding with PA6. Crucially, the abundant amide groups act as heterogeneous nucleation sites, inducing a PA6 transcrystalline layer at the interface, which optimizes stress transfer. Consequently, modified CF/PA6 composites exhibit improved tensile strength (+11.6%), impact strength (+49.5%), flexural strength (+16.2%), and flexural modulus (+16.6%). This work elucidates the mechanism of amide-induced interfacial crystallization, offering a new strategy for high-performance CF/thermoplastic composites.