Tight twist toughens nanotube fiber

Researchers from the University of Texas at Dallas and the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia have strengthened carbon nanotube yarn by introducing a tight twist as the nanotubes are spun. The method taps the secret of spinning discovered in the Late Stone Age: a tight twist produces a tough fiber.

Nanotubes are rolled-up sheets of carbon atoms that can be narrower than a nanometer and stronger than steel by weight. A nanometer is one millionth of a millimeter. Multiwall nanotubes contain several layers of successively larger tubes.

The researchers showed that it was possible to spin forests of multiwall nanotubes into multi-ply yarn that is as strong as 460 megapascals, which is close to the strength of fibers used in bulletproof vests. The technique produces yarn that can be knotted and that preserves the nanotubes' useful electrical and optical properties, according to the researchers.

The yarn could be used in flexible clothing that protects the wearer from ballistics, static discharge, and radio and microwave radiation. It could also be used in materials to dampen mechanical vibrations, provide structural reinforcement and efficiently dissipate heat. The yarn could also be used as filaments for incandescent light, flexible wires, electronic elements that could be woven into materials like textiles, artificial muscle, and supercapacitors that store large amounts of electricity.

The researchers grew dense forests of vertical nanotubes ranging from 8 to 15 nanometers in diameter and 300,000 nanometers, or 300 microns tall. A nanometer is one millionth of a millimeter. Pulling at the edge of the forest draws the nanotubes into filaments. Twisting the filaments produces fibers. A 200-micron wide forest edge yields a two-micron diameter fiber, and a 1-square-centimeter forest a 50-meter-long fiber, according to the researchers.

The work appeared in the November 19, 2004 issue of Science.