Carbon nanotubes have superlative strength and conductivity, but in the two decades since their discovery, it’s proved difficult to make long strands out of them that could take advantage of those properties. Now researchers at Rice University and Dutch materials company Teijin Aramid are making thread-like nanotube fibers that combine the electrical conductivity of metals with the strength of carbon composites, and are lightweight, flexible, and thermally conductive.
Carbon bright: This 46-gram light-emitting diode is held aloft by two 24-micrometer thick nanotube fibers. The fibers also carry electrical current to the bulb.
Teijin Aramid, based in Arnhem, Netherlands, and a leading producer of high-strength fibers, plans to commercialize the nanotube-based materials, likely first in wiring for planes and satellites, and eventually in electronic textiles and medical implants that resist corrosion.
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Individual carbon nanotubes are some of the strongest, most conductive known materials. But most attempts to build larger materials from them result in a tangled mess that has neither of these properties. The problem is that to make such materials, you need to align the nanotubes.
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In 2003, Rice University researchers led by Richard Smalley made the first carbon nanotube fibers by running a liquid suspension of nanotubes through a fiber-spinning machine of the same type used to make commercial polymer fibers like DuPont’s Kevlar and Twaron, which is made by Teijin Aramid. The rationale was that the nanotubes would flow through the liquid and line up with one another like logs floating on a river. This alignment should make the fiber stronger and more conductive. However, the properties of these early fibers were not very good, says Matteo Pasquali, who now leads the nanotube fiber project at Rice. While other groups turned to making nanotube sheets and fibers from dry materials, the Rice group stuck with its method.
At the time, it didn’t work very well with nanotubes, but Pasquali and Smalley believed if they could improve the spinning process, it would ultimately lead to fibers with better properties than the dry methods, and be amenable to large-scale manufacturing like that done with polymers.
Now that decision has paid off, says Pasquali. Working with Teijin Aramid, the Rice group has now made carbon-nanotube fibers that have more of the properties of individual nanotubes. They have an electrical conductivity close to copper’s, but are much stronger. They’re not quite as strong as conventional carbon fibers, but they’re much less brittle. And they’re more thermally conductive than metal or carbon fiber. That means nanotube fibers could replace these materials in existing applications in aerospace and electronics, and enable new technologies that take advantage of the fibers’ unique combination of strength, flexibility, and thermal and electrical conductivity. Pasquali envisions washable electronic textiles, lightweight wiring for planes, and eventually, more efficient wires for the electrical grid.
The filaments are about 25 micrometers thick and can be woven into thicker threads to hold up heavier loads, or to carry more current. Pasquali says the group can now produce the nanotube materials continuously, and that it takes a couple of hours to produce a few hundred meters. This work is described in the journal Science.
Marcin Otto, business development manager at Teijin Aramid, says that because the fibers are made using a wet-spinning process, they have better properties than those made from dry nanotubes. But, he concedes, Teijin Aramid will have to show it’s capable of manufacturing at larger scales.
Otto says Teijin Aramid is now looking into various potential markets. One possibility is lightweight multifunctional textiles for smart clothing that integrate medical sensors, antennas, and other devices, and can survive the stress of folding and resist corrosion in the washing machine. But early applications are likely to be in markets such as electrical wiring for aerospace and defense, where every ounce of weight is critical. First, the company has to do the necessary engineering and testing to make sure the fibers can be scaled up to make a reliable product.
