In-situ synthesized aramid nanoparticles for multiscale fiber reinforcement of polymer composites

Aramid fiber has attracted much attention in the field of ballistic protection because of their exceptional energy absorption capabilities, but their application in fiber-reinforced polymer (FRP) composites for structural uses has been limited. The limitation is mainly due to their smooth and chemically inert surfaces, leading to poor dispersion and weak interfacial strength in FRP composites. Here, a novel approach to address the limitation by in-situ synthesized aramid nanoparticles (ANPs) within a styrene-butadiene rubber (SBR) matrix is reported. The ANPs are formed through polycondensation of p -phenylenediamine and p -phthaloyl dichloride directly in SBR-cyclohexanone/N-methyl pyrrolidone solution. Those ANPs not only serve as nanoscale reinforcements to significantly enhance the mechanical properties of the SBR matrix, but also act as “bridges” to dramatically improve the interfacial bonding strength between aramid fibers and SBR matrix. Pullout tests demonstrated a significant increase in interfacial load from 75.0 N to 140 N for aramid fiber-reinforced rubber sheets and from 70.9 N to 302 N for aramid fabric-reinforced rubber sheets. Hydrogen bonding and π-π stacking interactions between ANPs and aramid fibers enable effective stress dispersion and transfer, mitigating interfacial stress concentration. The study provides a rather practical process to enhance aramid fiber-polymer matrix interfacial strength in FRP composites. • A novel approach to enhance interfacial bonding force between aramid fiber and polymer matrix is presented. • PPTA nanophase was created by in-situ synthesis in styrene butadiene rubber matrix. • Created aramid nanoparticles (ANPs) can act as “anchor” to secure aramid fiber in polymer matrix.