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

ABSTRACT 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.