Preparation and properties of wet-laid CF/AF hybrid-reinforced PA66 thermoplastic composites

Carbon fiber reinforced thermoplastic composites exhibit excellent properties such as low density and high strength. However, their performance is often limited by inhomogeneous fiber distribution arising from density differences between fibers and the resin matrix. This study addresses this limitation by fabricating high-performance AF/CF/PA66 composites using an innovative wet-laid hybrid approach. This method uniquely combines unconventionally long carbon fibers (4-8 cm) with short aramid fibers (AF). With the addition of 3 wt% and 3 mm length AF, the tensile strength, flexural strength, and impact strength reached 230.47 ± 5.2 MPa, 356.13 ± 8.7 MPa, and 72.49 ± 3.1 kJ·m -2 , respectively, representing increases of 37.86%, 47.91%, and 86.44% compared to the CF/PA66 composite without AF (167.53 ± 4.1 MPa, 240.77 ± 6.3 MPa, 38.88 ± 2.5 kJ·m -2 ). This enhancement is attributed to the formation of a carbon fiber-aramid fiber-carbon fiber (CF-AF-CF) interpenetrating entangled network by AF addition, which may facilitate stress transfer in the thickness direction and effectively enhances the stress transfer efficiency. Simultaneously, AF promotes the crystallization behavior of PA66 towards more favorable crystal forms, significantly enhancing the matrix’s structural properties. Consequently, the 3 wt% AF specimen exhibited the highest energy storage modulus of 10.01 GPa, indicating optimal interfacial bonding and structural stability. This work demonstrates a novel process-structure-property design strategy for high-performance thermoplastic composites.