A process has been developed that could lead to industrial production of nanotube fibers for threads and cables that are 100 times stronger than steel.
The process, developed by researchers at Rice University in Houston, Texas uses a strong acid to produce continuous fibers of single-walled carbon nanotubes.
“To produce large objects out of nanotubes, chemical processes must use a liquid that can disperse large concentrations of pristine tubes,” says Matteo Pasquali, assistant professor of chemical engineering. “Based on our findings, we believe superacids can be used to make macroscale fibers and sheets of nanotubes using methods that are quite similar to those in widespread use by the chemical industry.”
Carbon nanotubes are hollow cylinders of carbon just one atom thick.
Besides being 100 times stronger than steel, nanotubes are also one-sixth the weight. Kevlar, used in bulletproof body armor, is only about five times as strong as steel.
The strength and lightness of nanotubes has led to proposals for novel products. Plans are being developed, for example, for a space elevator that would use a carbon nanotube shaft.
Producing carbon nanotube fibers, however, is difficult because the tubes are attracted to each other and clump together.
To untangle them, researchers have used detergent and water solutions with less than one percent nanotubes by volume.
The concentration of nanotubes, however, is too low for industrial production, and the process produces impure nanotubes.
Pasquali and colleagues have found a solution.
They dissolve nanotubes in strong sulfuric acid to produce solutions with a concentration of up to 10 times more nanotubes than solutions produced using previous techniques.
“As the concentration increases, the nanotubes first align themselves into spaghetti-like strands and eventually they form tightly packed liquid crystals that can be processed into pure fibers,” says Pasquali.