Abstract: We have been exploring how the exceptional properties of carbon nanotubes (CNTs) can be extended to macro-scale CNT-spun yarn to hasten their practical application. I will introduce our research on high-strength few-walled CNT (FWCNT) spun yarn as an alternative to commercially available carbon fibers.

We first established the key structural requirements of vertically aligned CNT arrays, including CNT height, density, and the number of CNTs, for reproducible and continuous yarn formation by direct drawing and twisting from CNT substrates. The untreated CNT spun yarns exhibited a tensile strength of approximately 1.5 GPa and a Young’s modulus of approximately 100 GPa. Therefore, a major challenge was to enhance their mechanical properties to those of high-performance aerospace-grade carbon fibers, which have tensile strengths of approximately 7 GPa and Young’s moduli of approximately 320 GPa.

To address this challenge, we developed a high-speed Joule annealing (JA) process in which an electric current is applied to CNT-spun yarns as they are continuously treated at 1 cm s-1. When the treatment temperature exceeded 3000 K, the intensity ratio of a graphitic G band (~1590 cm^-1) and a defect-induced D band (~1350 cm^-1) of the Raman spectra of the CNT-spun yarns increased markedly, indicating structural improvement in the CNTs, which contributed to enhanced tensile strength.

Furthermore, to suppress slippage between individual CNTs and CNT bundles, we developed a technique for introducing fine graphene oxide or graphene sheets into the nanoscale spaces within the CNT yarns. By combining this nano-space reinforcement strategy with high-temperature JA treatment, we achieved a tensile strength of 6.4 GPa and a Young’s modulus of 320 GPa. These values are close to those of the highest-strength commercial carbon fibers, demonstrating the potential of CNT spun yarns as next-generation lightweight, high-strength structural fibers．

Keywords: Carbon nanotubes (CNT), high-strength carbon nanotube spun yarn, Joule annealing, nano-space reinforcement

Acknowledgements: This work was partially supported by JSPS KAKENHI Grant Number JP24K00928.

Biography: Yasuhiko Hayashi received his B.E., M.E., and D.E. degrees in electrical and computer engineering from the Nagoya Institute of Technology (NIT) in 1990, 1992, and 1999. He worked on semiconductor device modeling at Motorola Japan from 1992 to 1996, then served as Research Associate (1999) and Associate Professor (2007) at NIT. Since 2012, he has been a Professor at Okayama University and served as Vice Executive Director for Research from 2021 to 2024. He has also been a visiting researcher at the University of Cambridge, the University of Surrey, and the Technical University of Denmark, studying nanomaterials and nano physical properties. His current research includes synthesizing carbon nanomaterials, investigating their properties and device applications, developing perovskite solar cells and new perovskite materials, and advancing multivalent ion batteries, as well as synthesizing 2D TMDs and fabricating transistor devices.