Carbon nanotubes (CNTs) are attractive for a multitude of technological and life science applications because of their unique combination of mechanical, electrical and thermal properties. One important challenge for their incorporation into large-scale devices is the high-throughput and cost-efficient fabrication of high-quality, continuous CNT yarn. Now, Xiao-Hua Zhong and co-workers at Tianjin University in China1 have successfully fabricated kilometer-long, continuous CNT yarns that have high uniformity and an internal structure that makes them versatile for use in a wide range of applications.

Fig. 1: (Left) Continuous carbon nanotube yarns spun directly by catalytic CVD reaction synthesis. (Right) Scanning electron microscopy images of the hollow structure of the carbon nanotube yarn (upper) and the multiple layered carbon nanotube walls (lower).© 2010 nanowerk.com

The fabrication of these CNT yarns relies on the self-assembly of CNT fibers in a heated hydrogen gas flow from a chemical vapor deposition (CVD) reaction with a mixture of acetone and ethanol as carbon sources. Under the right conditions, at the outer edges of the heated furnace through which the gas flows, van der Waals interactions cause the self-assembly of CNTs into a sock-like structure. The ‘sock’ is extracted with water and acetone at the outlet of the reactor, where it immediately shrinks into a fiber that is spun into a CNT yarn (Fig. 1).

Commenting on the findings, Ya-Li Li, who leads the project, says: “The yarn produced is essentially continuous over kilometers in length.” The CNT throughput is high, up to 1200 meters per hour, and the as-spun fibers display macroscopic uniformity. They can be handled like conventional yarns and woven into designed fabrics.

Crucially, the specific internal structure of the yarn allows it to be tailored. “The novel aspect of our yarn is that it is made of several tens of multiple layers of carbon nanotubes with nanometer thickness,” explains Li. “It can be made either hollow or dense by controlling the spinning process.” In addition, the direction of the CNTs can be designed to be either parallel to the yarn axis or crossed. This has a profound effect on the mechanical and electrical properties of the resulting yarn, as evidenced in strength and tensile tests, as well as on its conductivity.

The process is ready for large-scale production, according to Li. “We are currently enlarging the process for the fabrication of quantity carbon nanotube yarns, increasing yarn strength, and developing woven fabrics and applications in composites, sensors, electrochemical systems and bio-applications.”