Enhancing the Interfacial Interactions and Thermal Oxidative Mechanical Properties of Aramid Fiber‐Reinforced Epoxy Composites Through Hyperbranched Epoxy‐Grafted Multi‐Walled Carbon Nanotubes

ABSTRACT Enhancing the interfacial properties of aramid fiber‐reinforced polymer (AFRP) composites while maintaining thermal stability remains a significant challenge in advanced composite engineering. This study introduces an innovative approach by incorporating carbon nanotubes (CNTs) functionalized with hyperbranched epoxy (HPEP) to construct multi‐level micro/nano interfaces in AFRP composites. The grafting efficiency of HPEP onto CNTs was confirmed to be 14.14%, facilitating superior dispersion and interfacial bonding. Incorporating 2 wt% CNTs‐g‐HPEP into AFRP composites resulted in remarkable increases of 41.3% in flexural strength and 30.9% in interlaminar shear strength. These composites, featuring multi‐level micro/nano interfaces, demonstrated exceptional retention of mechanical properties after thermal aging. This enhancement is attributed to the synergistic reinforcement effect of CNTs‐g‐HPEP on the matrix‐fiber interface. The epoxy groups in CNTs‐g‐HPEP co‐cured with the polymer matrix, while the flexible hyperbranched chains enhanced the mechanical interlocking with AFs. They also show exceptional thermal‐oxidative mechanical performance, with high mechanical retention ratios after thermal aging. The thermal failure analysis indicated that with the increasing temperature, the failure mode of the AFRP composite gradually shifted from fiber‐matrix debonding to matrix degradation. This study provides a robust strategy for the design and development of next‐generation high‐performance AFRP composites, offering significant potential for applications in demanding environments.