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Industrial Process Devised for Carbon Nanotube Fibers

Light bulb suspended and powered by carbon nanotube fibers (Rice University)

Light bulb suspended and powered by carbon nanotube fibers (Rice University)

Engineers and materials scientists from the U.S., Netherlands, and Israel developed an industrial-scale process for spinning carbon nanotubes into fibers for a range of commercial products. The team led by chemical engineering professor Matteo Pasquali at Rice University in Houston published its findings in this week’s issue of the journal Science (paid subscription required).

Pasquali, with colleagues from Rice, the Dutch industrial fibers company Teijin Aramid, Israel’s Technion Institute, and Air Force Research Laboratory, created a new type of carbon nanotube fiber that acts like a textile, yet conducts heat and electricity like a metal. “It looks like black cotton thread,” says Pasquali, “but behaves like both metal wires and strong carbon fibers.”

Carbon nanotubes — nearly as thin as a strand of DNA — are the basis for many recent breakthroughs in advanced materials. They are about 100 times stronger than steel, but one-sixth the weight. These properties, along with the ability to conduct electricity and heat have led carbon nanotubes to be used in new types of light-activated semiconductors, drug-delivery devices, and sponges to soak up oil.

But carbon nanotubes have other characteristics that make mass production difficult, including brittleness, lack of uniform quality, and clumping rather than maintaining fiber-like properties. Some labs have succeeded in growing nanotubes into fibers, but these processes are too slow for commercial production.

In this project, the team adapted a process called wet spinning that dissolves the carbon nanotubes in chlorosulfonic acid that allows a viscous nanotube solution to be squirted through tiny filters to form long strands. The late Richard Smalley, a nanotechnology pioneer at Rice, developed wet-spinning methods for nanotubes in the last decade, but Teijin Aramid adapted the technique to produce industrial-scale fibers, such as its Twaron used in bulletproof vests. In 2010, Teijin Aramid began a partnership with Rice, with the company’s wet-spinning experts collaborating with Rice scientists throughout the project.

The fibers created by the new process, say the researchers, have 10 times the tensile strength, and electrical and thermal conductivity of the best previously reported wet-spun carbon nanotube fibers, comparable to copper, gold and aluminum wires. Pasquali attributes improvements in strength and conductivity of the fibers to the help from Teijin Aramid. Co-author Junichiro Kono, a Rice electrical engineering professor says, “The research showed that the electrical conductivity of the fibers could be tuned and optimized with techniques that were applied after initial production.”

Pasquali says the light weight and flexibility of carbon nanotube (CNT) fibers have advantages over metal wires, particularly for data and low-power cables. “In many cases, people use metal wires that are far more thick than required for the electrical needs, simply because it’s not feasible to produce a thinner wire,” notes Pasquali. “Data cables are a particularly good example of this.”

Marcin Otto, Teijin Aramid’s business development manager and co-author of the Science paper says, “we have been very excited by the interest of innovative medical doctors and scientists exploring the possibilities to use CNT fiber in surgical operations and other applications in the medical field.” In addition to data and low-power cables, Otto anticipates carbon nanotube fibers used to integrate light weight electronic components, such as antennas, into composites, or replacing cooling systems in electronics where the high thermal conductivity of carbon nanotube fiber can help dissipate heat.

In the following video, Pasquali and colleagues demonstrate the wet-spinning process creating the fibers.

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