Constructing regulable soft‐rigid active interface structure of CF / PEEK composites using aqueous sizing agent with HA nanomaterial

Abstract The increasing demand for carbon fiber/polyether‐ether‐ketone (CF/PEEK) composites in marine and aerospace engineering is driven by their potential for weight reduction and enhanced structural flexibility. However, the inherent weak interface poses a challenge, leading to stress concentration and structural failures. Herein, aqueous PEKC‐COOH sizing agent on CF as a soft unit (SCF) and hydroxyapatite (HA) nanomaterial as a rigid unit establish a regulable active interface structure, synergistically enhancing the interface adhesion through mechanical interlocking and chemical bonding of the CF/PEEK composites. Under external loading, the PEKC‐COOH sizing agent allows for uncurling of molecular chains at the interface, promoting slip of HA nanomaterials and dissipating a significant amount of energy during fracture progression. The SCF‐HA/PEEK composites exhibited significant enhancements in interlaminar shear strength and flexural strength, with an increase of 65.1% and 49.8%, respectively, compared with the pristine composites. Meanwhile, the salt‐spray resistance of the composites has been significantly improved. Following a 72‐h salt spray test, the ILSS retention ratios of modified SCF‐GB/PEEK composites were determined to be 91.7%. Remarkably, the use of cationic, non‐ionic, and zwitterionic surfactants reduced the growth time of HA on the fiber surface in simulated body fluids to 15 min compared to several days using conventional methods. This study not only improves production efficiency and reduces manufacturing costs but also provides a research foundation for industrial manufacturing. Furthermore, the novel interface structure design broadens the applicability of CF/PEEK composites in hygrothermal and salt‐spray environments. Highlights Regulable interface was formed by in situ growth of HA on fiber sizing agent. HA nanomaterial growth time in SBF was reduced from several days to 15 min. Modified composites increase ILSS by 65.1% and flexural strength by 49.8%. Modified composites maintain 91.7% ILSS after a 72‐h salt‐spray resistance test.