Meso through Nano Scale Characterization of CNT Yarn Strength

J. Severino, J-M Yang, L. Carlson
University of California Los Angeles, US

Keywords: carbon nanotube yarn strength composite fiber

Summary:

The ultimate goal of nanocomposite yarns is utilizing the extraordinary strength of carbon nanotubes to produce ultra-strong fibers that integrate into traditional composite systems. Single nanotubes have measured strength between 50 – 150 GPa; however, when combined to form macroscopic yarns the strength is below traditional carbon fibers. This disparity is caused by a variety of imperfections in the yarns. Therefore, we characterize the non-ideal features and how each contributes to strength reduction. In this work a top down approach is taken on standard and thermally annealed CNT yarns. First, at the meso scale, the yarns’ strength is tested in tension. Then internal structures and microscopic arrangements are observed with a focused ion beam (FIB) and a field emission SEM. Finally, the nanostructure is characterized with a high resolution TEM. The features observed include: multiwall nanotubes, bundles, bridges, porosities, folds, twist and non-graphitic contamination. Because each feature affects strength differently, the relative contributions are discussed. With this knowledge it is possible to focus future research on areas that will significantly increase yarn strength.