Dual‐Interface Enhancement in Glass Fiber/PEN Composites via a PEN‐Based Sizing Agent for Superior Mechanical Performance

ABSTRACT High‐performance thermoplastic composites offer advantages such as lightweightness, high strength, recyclability, impact resistance, and rapid molding. However, they also face challenges, including high processing temperatures, weak interfacial bonding, and relatively high costs. This study addresses the interfacial issues of thermoplastic composites by innovatively developing a sizing agent for glass fiber‐reinforced poly(arylene ether nitrile) (PEN) thermoplastic composites, which is a carboxyl‐functionalized PEN. The surface morphology, composition, and roughness of the fibers were characterized to investigate the influence of fiber surface modification on composite performance and to elucidate the underlying mechanism to enhance the mechanical properties of the composites. The sizing agent chemically adheres to the fiber surface and subsequently forms semicircular protrusions during the nonsolvent‐induced phase separation process, increasing surface roughness to enhance the wetting of PEN resin on the fiber fabric, therefore synergistically enhancing the interfacial bonding strength through a dual mechanism of “chemical anchoring and physical interlocking.” After modification, the average surface roughness of the fibers increased from 10.2 to 117.0 nm, significantly improving the resin matrix's wettability on the fibers. Additionally, rheological experiments demonstrated that this interfacial reinforcement effectively suppresses the decrease in resin viscosity at high temperatures. The mechanical properties of the composite materials with PEN‐COOH‐sized fibers were substantially improved. Compared with untreated fibers, the modified composites exhibited a bending strength increase from 515 to 766 MPa (≈49% improvement) and an interlaminar shear strength increase from 69 to 85 MPa (≈23% improvement). This study provides a novel high‐temperature resistant sizing agent formulation for the preparation of high‐performance thermoplastic composites, thereby broadening the application of PEN in glass fiber composites.