Polyethyleneimine–Polydopamine Coating and NH ₂ /COOH‐Carbon Nanotubes Synergistically Reinforced Continuous Aramid Fiber/Unsaturated Polyester Resin Composites

ABSTRACT Aramid fiber (AF)‐reinforced composites face significant limitations in applications such as deep‐sea equipment and aerospace due to their poor interfacial compatibility and low bonding strength. This study presents an innovative and scalable strategy for constructing a nano‐hierarchical reinforcement interface on AF to fundamentally address this issue. A multifunctional interlayer was first constructed using polyethyleneimine (PEI) and polydopamine (PDA), on which both carboxylated and aminated carbon nanotubes (COOH‐CNTs and NH 2 ‐CNTs) were co‐anchored to produce the final product, denoted as C/N‐CNTs‐PP‐AF. The distinctive dual‐CNT configuration produced a stable electrical resistance in the range of 51.57–84.20 MΩ by forming a continuous conductive network. More importantly, C/N‐CNTs‐PP‐AF/unsaturated polyester (UP) composites exhibited significant enhancement in properties, which corresponded to an interfacial strength of 39.60 MPa (an 81.15% increase) and tensile strength of 1404.25 MPa (an 89.45% improvement). The approach leverages multifaceted interfacial interactions to enable stable CNT grafting and enhanced adhesion. This work not only effectively addresses weak bonding at the AF/UP interface but also establishes a new paradigm for the design of high‐performance fiber‐reinforced composites with integrated functionalities.