Polyethyleneimine–Polydopamine Coating and NH2/COOH-Carbon Nanotubes Synergistically Reinforced Continuous Aramid Fiber/Unsaturated Polyester Resin Composites

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.