Dual-Scale Synergistic Surface Modification of Carbon Fiber Fabric for Enhanced Interfacial Bonding and Mechanical Properties of PA6 Composites

Carbon fiber fabric (CFF)/polyamide 6 (PA6) composites suffer from poor interfacial bonding due to incomplete fiber wetting and void formation. This study presents a dual-scale synergistic surface modification strategy combining mild alkaline etching with 3-aminopropyltriethoxysilane (KH550) coating. Optimal etching parameters were established at 3 h with 5 wt% NaOH solution at 60°C. The synergistic mechanism operates at micrometer and nanometer scales: alkaline etching creates microscopic grooves and introduces oxygen-containing functional groups, while KH550 coating forms strong covalent Si  O  C bonds and hydrogen bonding with the PA6 matrix. CFF/PA6 composites were prepared using resin transfer molding (RTM) with in situ polymerization. The optimized K-CFF/PA6 composite exhibited superior mechanical properties: tensile strength of 688.1 MPa (29.6% higher than R-CFF/PA6 composite), Young's modulus of 29.2 GPa (18.7% higher), flexural strength of 472.3 MPa (75.5% higher), and flexural modulus of 23.1 GPa (43.9% higher). Most notably, the composite achieved the lowest porosity (0.498%) among reported materials, with interfacial layer thickness increasing from 540 to 930 nm. Comprehensive characterization confirmed the dual-scale synergistic mechanism. This strategy offers significant advantages over conventional oxidation methods by preserving fiber integrity while achieving superior mechanical performance, rendering it suitable for industrial-scale applications in aerospace and automotive sectors.