Construction of Aramid Nanofiber-Based Interphase by In Situ Controlled Polymerization and Mechanism for Interfacial Reinforcement of Aramid Fiber Composites

Aramid Fiber Reinforced Composites (AFRCs) rely on a strong interfacial bond between aramid fiber and polymeric matrix to yield the high strength and toughness expected by a composite material. But they tend to have poor interfacial bonding between the chemically inert fibers and the matrix polymers. In order to construct a strong interphase in aramid fiber composites, we present a novel interphase construction strategy that leverages in situ synthesized aramid nanofibers (ANFs), which are synthesized directly in natural rubber (NR) via a one-step polymerization. The ANFs then, in constructing the AFRCs, serve both as functional fillers within the NR matrix and as nanoscale surface modifiers for aramid fibers and fabrics. The ANFs exhibit compact morphologies and excellent dispersion, and they form a rigid three-dimensional network in NR that improves tensile strength, modulus, and toughness. Through dip-coating, ANFs are anchored onto aramid surfaces, which significantly increases surface roughness and functional group density without altering the bulk fiber structure. The excellent compatibility between ANFs and NR gives rise to a gradient interfacial region that enhances stress transfer via physical entanglement and hydrogen bonding. Multiscale characterization reveals improved interface behavior and mechanical integrity, and under the optimal conditions, the pull-out force increases by 207.4% and 286.8% for the fiber-based and fabric-based composites, respectively. This dual reinforcement approach is a scalable route to tailor interfacial properties and lays the groundwork for the cross-scale design of high-performance aramid fiber composites.