Carnegie Mellon University scientists have developed an attractive way to make discrete carbon nanoparticles for electrical components used in industry and research. This method employs polyacrylonitrile (PAN) as a nanoparticle precursor.
Strong and versatile carbon nanotubes are finding new applications in improving conventional polymer-based fibres and films. For example, composite fibres made from single-walled carbon nanotubes (SWNTs) and polyacrylonitrile, a carbon fibre precursor, are stronger, stiffer and shrink less than standard fibres.
Nanotube-reinforced composites could ultimately provide the foundation for a new class of strong and lightweight fibres with properties such as electrical and thermal conductivity unavailable in current textile fibres.
"We are going to have dramatic developments in the textile materials field over the next 10 or 20 years because of nanotechnology, specifically carbon nanotubes," predicted Satish Kumar, a professor in Georgia Tech's School of Polymer, Textile and Fiber Engineering. "Using carbon nanotubes, we could make textile fibres that would have thermal and electrical conductivity, but with the touch and feel of a typical textile. You could have a shirt in which the electrically-conducting fibres allow cell phone functionality to be built in without using metallic wires or optical fibres."
Thanks to the work of Kumar and researchers at the Air Force Research Laboratory, nanotubes have already found their way into fibres known as Zylon, the strongest polymeric fibre in the world. By incorporating 10 percent nanotubes, research has shown that the strength of this fibre can be increased by 50 percent.
Recently, Kumar's research team has been collaborating with Richard Smalley, a Rice University professor who received a 1996 Nobel Prize for his work in developing nanotubes, which are of great interest because of their high strength, light weight, electrical conductivity and thermal resistance.
The researchers have developed a technique for producing composite fibres containing varying percentages of carbon nanotubes, up to a maximum of about 10 percent. Produced by Rice University and Carbon Nanotechnologies, Inc., single-walled nanotubes exist in bundles 30 nanometers in diameter containing more than 100 tubes.
To produce composite fibres, the bundles are first dispersed in an organic solvent, acid or water containing surfactants. Polymer materials are then dissolved with the dispersed nanotubes, and fibres produced using standard textile manufacturing techniques and equipment. The resulting composite fibres have the similar touch and feel as standard textile fibres.
Addition of carbon nanotubes to traditional fibres can double their stiffness, reduce shrinkage by 50 percent, raise the temperature at which the material softens by 40 degrees Celsius and improve solvent resistance. Kumar believes these properties will make the composite fibres valuable to the aerospace industry, where the improved strength could reduce the amount of fibre needed for composite structures, cutting weight.
"If you can increase the modulus (stiffness) by a factor of two, in many applications you can also reduce the weight by a factor of two," Kumar noted.
But the greatest impact of carbon nanotubes will be realized only if researchers can learn how to break up the bundles to produce individual nanotubes, a process called exfoliation. If that can be done, the quantity of tubes required to improve the properties of fibres could be reduced from 10 percent to as little as 0.1 percent by weight That could help make use of the tubes, which now cost hundreds of dollars per gram –feasible for commercial products.
Including individual nanotubes in composite fibres could help improve the orientation of the polymer chains they contain, reducing the amount of fibre entanglement and increasing the crystallization rate. That could introduce new properties not currently available in fibres.
"If we can do this, that would conceptually change how fibres are made," Kumar said. "Having a very tough temperature resistant material with a density of less than water seems like a dream today, but we may be able to see that with this new generation of materials."
Beyond breaking up the nanotube bundles, researchers also face a challenge in uniformly dispersing the carbon nanotubes in polymers and properly orienting them.
In addition to aircraft structures, Kumar sees nanotube composite fibres bringing electronic capabilities to garments, perhaps allowing cellular telephone or computing capabilities to be woven in using fibres that have the touch and feel of conventional textiles. But producing conducting fibres would require boosting the nanotube percentage to as much as 20 percent.
To advance these concepts, Kumar hopes to form a "Carbon Nanotube-enabled Materials Consortium" at Georgia Tech to conduct both basic and applied research in areas of interest to industry.
He expects composite fibres based on carbon nanotubes to bring about the most significant changes to the textile industry since synthetic fibres were introduced in the 1930s.
"In 1900, nylon, polyester, polypropylene, Kevlar and other modern fibres did not exist, but life today seems to depend on them," he said. "The rate at which technology is changing is increasing, so much more dramatic changes can be expected in the next 100 years. Every major polymer fibre company in the world is now paying attention to the potential impact of carbon nanotubes."