Enhanced Mechanical Properties of Carbon Fiber Reinforced Phthalonitrile Resin Matrix Composites at Elevated Temperature via Cyano‐Functionalized Graphene Oxide

ABSTRACT Phthalonitrile (PN) resin matrix composites exhibit outstanding heat resistance owing to their highly crosslinked network and rigid aromatic heterocyclic structure. However, the intrinsic brittleness of PN resin and weak fiber–matrix interfacial adhesion severely impair the load‐bearing capacity of PN composites under high‐temperature conditions, especially with respect to interlaminar shear strength (ILSS). To address this inherent limitation, a new reinforcement strategy was developed. Cyano‐functionalized graphene oxide (GO‐CN), showing excellent thermal stability and good compatibility with PN resin, was prepared. Chemical structure, rheological properties, thermal stability, free volume fraction and dynamic mechanical properties of GO‐CN/PN blends were characterized. The results demonstrate that GO‐CN simultaneously improves the stiffness and toughness of PN resin through stronger load transfer capacity and looser chain packing, while enhancing the interfacial adhesion by promoting the conversion of aromatic heterocyclic products, thereby reinforcing the mechanical properties of PN composites at elevated temperature. Compared with PN composites, GO‐CN/PN composites exhibited a highest 103% enhancement in ILSS after 450°C/2 h exposure, while its flexural modulus and flexural strength were also improved. Notably, the addition of GO‐CN has no negative effect on glass transition temperature (Tg). This work suggests that GO‐CN is a kind of highly promising heat‐resistant nanofiller for carbon fiber reinforced PN composites designed for long‐duration, high‐temperature load‐bearing applications.