Molecular‐Bridge Interfacial Engineering of High‐Strength BF / PPO Composites Enabled by a Waterborne Self‐Emulsified Amphiphilic Sizing

ABSTRACT Basalt fiber (BF)–reinforced polyphenylene oxide (PPO) composites are promising for high‐performance wave‐transparent applications but are limited by intrinsically weak interfacial adhesion. To address this challenge, we developed a waterborne, self‐emulsified amphiphilic sizing agent inspired by reversible addition–fragmentation chain transfer (RAFT) polymerization, polymerization‐induced self‐assembly (PISA), and the “like‐dissolves‐like” principle. A styrene–maleic anhydride copolymer was grafted with triethanolamine to form an amphiphilic precursor that acted as a reactive emulsifier for styrene emulsion polymerization, ultimately yielding a self‐stabilized amphiphilic nanoemulsion. This sizing layer establishes a molecular bridge at the BF/PPO interface: hydrophilic PSMA‐g‐TEA segments covalently bond with surface SiOH groups to generate stable SiOC linkages, while hydrophobic polystyrene segments entangle with the PPO matrix. As a result, the tensile strength of BF monofilaments increased from 1.243 GPa (untreated) to 1.506 GPa, and the interfacial shear strength (IFSS) of the composites improved from 10.32 to 28.22 MPa. Requiring no additional emulsifiers or organic solvents, this environmentally benign and scalable strategy effectively overcomes interfacial incompatibility, providing an efficient route to high‐strength, low‐loss BF/PPO composites for advanced wave‐transparent structural applications.