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Rice Team Make Breakthrough in Nanotube Processing

13 November 2009

This week, Rice University scientists have unveiled a method for industrial-scale processing of pure carbon-nanotube fibres, producing nanotube-based fibres that are several metres long, which could be used in a variety of applications.

The result of a nine-year program, the method builds upon tried-and-true processes that chemical firms have used for decades to produce plastics.

The new process builds upon the 2003 Rice discovery of a way to dissolve large amounts of pure nanotubes in strong acidic solvents like sulfuric acid. The research team subsequently found that nanotubes in these solutions aligned themselves to form liquid crystals that could be spun into monofilament fibers about the size of a human hair.

""That research established an industrially relevant process for nanotubes that was analogous to the methods used to create Kevlar from rodlike polymers, except for the acid not being a true solvent,"" said Wade Adams, director of the Smalley Institute and co-author of the new paper. ""The current research shows that we have a true solvent for nanotubes -- chlorosulfonic acid -- which is what we set out to find when we started this project nine years ago.""

Following the 2003 breakthrough with acid solvents, the team methodically studied how nanotubes behaved in different types and concentrations of acids. By comparing and contrasting the behavior of nanotubes in acids with the literature on polymers and rodlike colloids, the team developed both the theoretical and practical tools that chemical firms will need to process nanotubes in bulk.

""Kevlar, the polymer fiber used in bulletproof vests, is about five to 10 times stronger than our strongest nanotube fibers today, but in principle we should be able to make our fibers about 100 times stronger,"" says Rice's Matteo Pasquali, a paper co-author and professor in chemical and biomolecular engineering and in chemistry. ""If we can realize even 20 percent of our potential, we will have a great material, perhaps the strongest ever known.

""The electrical conductivity is already pretty good,"" he said. ""It's about the same of the best-conducting carbon-carbon fibers, and that could be improved 200 times if better production methods for metallic nanotubes can be found.""

The new research appears just as the Smalley Institute prepares for a 10th anniversary celebration Nov. 5 of the creation of Smalley's ""HiPco"" reactor, the first system capable of producing high-quality nanotubes in bulk. HiPco, short for high-pressure carbon monoxide process, broke the logjam on nanotube production and cleared the way for more scientific study and for industry to begin using them in some materials. Industrial nanotube reactors today generate several tons of low-quality carbon nanotubes per year, and the worldwide market for nanotubes is expected to top $2 billion annually within the next decade.

But a final breakthrough remains before the true potential of high-quality carbon nanotubes can be realized. That's because HiPco and all other methods of making high-end, ""single-walled"" nanotubes generate a mixture of nanotubes with different diameters, lengths and molecular structures. Scientists worldwide are scrambling to find a process that will generate just one kind of nanotube in bulk, like the best-conducting metallic varieties, for instance.

""One good thing about the process that we have right now is that if anybody could give us one gram of pure metallic nanotubes, we could give them one gram of fiber within a few days,"" Pasquali said.