"The unique electrical and mechanical properties of a carbon nanotube are mainly exhibited along its axis direction," Shoushan Fan of Tsinghua University told nanotechweb.org. "If long nanotubes can be obtained, they can be used to create macroscopic nanotube structures that maintain the unique properties of the nanotube. It's difficult to infinitely increase the length of nanotubes by growth - our work offers an alternative method to obtain nanotube yarns of any desired length, which should help the remarkable properties of carbon nanotubes to be realized at a macroscopic level."

The scientists discovered the technique whilst attempting to pull a bundle of carbon nanotubes out of an array of nanotubes several hundred microns high on a silicon substrate. Instead, they managed to draw out a continuous yarn of nanotubes, a process they compare to drawing a thread from a silk cocoon.

The researchers found they could only draw continuous yarns from superaligned arrays in which the nanotubes are aligned parallel to one another and held together in bundles by van der Waals forces. The yarns appear as thin ribbons a few hundred microns wide that contain parallel threads with diameters of several hundred nanometres.

A light bulb filament made from the yarn emitted light for 3 hours at 70 V. After this treatment, the yarn's conductivity and tensile strength both increased, indicating that some welding may have occurred at the connection points between the tubes. The scientists also made a polarizer from the yarn.

"Our pure carbon nanotube yarn, after proper heat treatment, should be able to be woven into a variety of macroscopic objects for various applications, just like silk thread in the textile industry," added the researchers.

Now the team is working to increase the strength of the joints between the nanotubes in the yarn and looking at ways to extend the yarn's applications. The scientists reported their work in Nature.