Effect of a carbon nanotube coating on friction and impact performance of Kevlar

Because surface treatments of high-performance fibers have previously resulted in increased friction and improved impact performance, it was of interest to evaluate the influence of multi-walled carbon nanotubes (MWNTs) on impact performance and contributing constituent properties of Kevlar. Kevlar K129 yarns and fabrics were modified via sonication in a solution of N-methylpyrrolidone (NMP) and MWNTs. This method has the potential to both improve the intrinsic properties of the fibers themselves as well as increase the friction, with very low mass addition. Tensile, static friction, and pull-out tests were performed to compare the properties of MWNT-treated materials to neat. As a result of MWNT augmentation, yarn modulus increased up to 15 %, and static and kinetic friction coefficients increased up to 30 %. Yarn pull-out tests revealed up to a 230 % increase in the forces required to pull-out yarns. To study the effects of MWNT augmentation on dynamic performance, low-velocity impact tests of steel spheres on a single ply of fabric were performed. These experiments demonstrated approximately 50 % increase in ballistic limit for MWNT-treated Kevlar with negligible (0.4–1.4 %) increase in mass. Entanglement among MWNTs along with increased surface roughness and surface area increased the resistance to motion, improving impact performance by increasing the energy required to pull-out yarns from the textile, while inhibiting textile windowing and driving a larger number of yarn failures. The observed changes in fabric response suggest that MWNT treatments have the potential to improve the ballistic limit of fabrics through increased interfilament and interyarn friction without compromising fiber strength or adding significant mass.