Dual-Mechanism Enhanced Basalt Fiber/Polyphenylene Oxide (BF/PPO) Composites: Integrating Chemical Bonding and Mechanical Interlocking Through PPO-MAH/CNTs Hybrid Sizing

Basalt fiber (BF) has been regarded as a promising reinforcement material for high-strength composites because of its good mechanical properties, thermal stability, and eco-friendliness. However, the inherent interfacial incompatibility between inorganic BF and organic polyphenylene ether (PPO) resin severely limits the properties of basalt fiber-reinforced polyphenylene ether (BF/PPO) composites. This work employs maleic anhydride-grafted polyphenylene ether (PPO-MAH) and carboxylated multi-walled carbon nanotubes (CNTs-COOH) as a dual-functional hybrid sizing to improve the interfacial interaction of BF/PPO composites based on synergistic chemical bonding and mechanical interlocking. Compared with the unmodified BF/PPO composite, the interlaminar shear strength, flexural strength, and tensile strength of modified BF/PPO composites increase by 64.0%, 39.8%, and 63.4%, respectively. Furthermore, these modified BF/PPO composites exhibit excellent flame retardancy and display rapid self-extinguishing behavior and no dripping due to CNT-induced carbonization and a dense char layer. These results provide a practical, eco-friendly, and efficient approach to simultaneously improve the interfacial adhesion, mechanical properties, and flame retardancy of BF/PPO composites and enlarge their applications for aerospace, automotive, and defense applications.