Super Fibers: Nanotubes make tough threads

The superior mechanical and electrical properties of carbon nanotubes have intrigued materials scientists for a decade. But they’ve struggled to take advantage of the hollow tubes, just nanometers wide, for macroscopic projects.

FUTURISTIC FIBERS. Materials scientists used carbon nanotubes to make two electricity-storing supercapacitors (black threads) that they inserted into cloth. The woven area is a little more than 2 centimeters long. A. Dalton et al.

Now, researchers have spun the tubes into composite fibers that are tougher than steel, Kevlar, or spider silk. The new fibers appear to be tougher than any other synthetic or natural material, says Ray Baughman of the University of Texas at Dallas in Richardson. Toughness indicates how much energy a material can absorb before breaking.

By modifying a process developed by French researchers (SN: 12/16/00, p. 398), Baughman’s team spins fibers made of carbon nanotubes and polyvinyl alcohol, a common industrial polymer. In the June 12 Nature, Baughman and his colleagues describe the finished threads, which are the width of a human hair and 100 to 200 meters long.

The achievement is “very good news for the field of nanotubes,” says Philippe Poulin of the Paul Pascal Research Center in Passac, France, one of the researchers who developed the technique that Baughman’s team modified.

The Texas researchers tested their fibers’ mechanical properties and compared them with known values for 3,000 other materials. The fibers are 20 times as tough as steel wire, 17 times as tough as the Kevlar used in bulletproof vests, and 4 times as tough as spider silk–a natural material whose renowned toughness researchers have long tried to mimic (SN: 08/17/02, p. 100: Available to subscribers at Spinning Fine Threads: Silkworms coerced to make better silk). The nanotube fibers are also stronger than spider silk and Kevlar, meaning they can support more weight.

“The results are the best I have seen from nanotube-composite materials,” comments Otto Zhou of the University of North Carolina at Chapel Hill. “This is a big step toward eventual utilization of carbon nanotubes . . . in composites, which has been envisioned since the discovery of carbon nanotubes more than 10 years ago.”

“This fiber will provide for a new generation of high-strength fabrics and energy-absorbing materials, such as vehicle armor,” suggests Ken Smith of Carbon Nanotechnologies, a Houston company that supplies Baughman with carbon nanotubes.

The fibers’ extraordinary properties could also make them candidates for safety harnesses, explosion-proof blankets, or bulletproof vests, suggests Baughman. He cautions, however, that the fibers haven’t yet been tested for antiballistic capabilities.

Baughman and his coworkers have already fashioned the fibers into electricity-storage devices called supercapacitors, which they incorporated into ordinary cloth. This exercise demonstrates the fibers’ potential for electronic textiles, such as military uniforms with built-in antennas, sensors, or tiny batteries for powering communications equipment, he says.

The most exciting thing about the new nanotube work is that the supertough fibers can now be made available to many researchers, says James Von Ehr, the founder of Zyvex, a firm based in Richardson, Texas, that’s developing carbon nanotube composites and other nanotechnology products. Ehr personally donated the seed money that established the NanoTech Institute at the University of Texas where Baughman and his colleagues work.

Right now, nanotube researchers agree, the biggest hurdle to exploiting the new fibers is the cost and limited availability of the nanotubes Baughman uses, known as the single-walled carbon nanotubes.

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