Superstrong Carbon Nanotube Yarns by Developing Multiscale Bundle Structures on the Direct Spin‐Line without Post‐Treatment

Super strong fibers, such as carbon or aramid fibers, have long been used as effective fillers for advanced composites. In this study, the highest tensile strength of 5.5 N tex(−1) for carbon nanotube yarns (CNTYs) is achieved by controlling the micro‐textural structure through a facile and eco‐friendly bundle engineering process in direct spinning without any post‐treatment. Inspired by the strengthening mechanism of the hierarchical fibrillary structure of natural cellulose fiber, this study develops multiscale bundle structures in CNTYs whereby secondary bundles, ≈200 nm in thickness, evolve from the assembly of elementary bundles, 30 nm in thickness, without any damage, which is a basic load‐bearing element in CNTY. The excellent mechanical performance of these CNTYs makes them promising substitutes for the benchmark, lightweight, and super strong commercial fibers used for energy‐saving structural materials. These findings address how the tensile strength of CNTY can be improved without additional post‐treatment in the spinning process if the development of the aforementioned secondary bundles and the corresponding orientations are properly engineered.