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Longest Nanofibres Bring Textile Advance

19 March 2004

Scientists at the University of Cambridge Have Manufactured Fibres Out of Strawlike Carbon Nanotubes.

They have developed a new method of making nanotube fibres similar to spooling yarn out of a ball of wool. Using ethanol as a source of carbon, the researchers reacted it with the chemicals ferrocene and thiophene and shot the mixture into a furnace heated to more than 1,000 degrees.

“Initially we were looking for high-efficiency methods of producing carbon nanotubes that could be scaled up commercially,” said Alan Windle, who led the research. “To this end, we focused on a vapour-phase synthesis route instead of involving substrates and surfaces. We then found that by thinking in terms of polymer technology we had the opportunity of withdrawing carbon nanotubes from the CVD [chemical vapour deposition] furnace as a continuous fibre and winding this up.”

The starting material for generating the nanotubes was ethanol containing 0.23 to 2.3 wt% ferrocene, and between 1.0 and 4.0 wt% thiophene. Windle and colleagues injected this solution from the top of a furnace into a hydrogen carrier gas. Iron nanoparticles catalysed the reaction: nanotubes grew in the furnace’s hot zone at a temperature of 1050- 1200 °C. The nanotubes formed an aerogel, which the scientists say appeared as “elastic smoke”.

The team found that they could wind the aerogel onto a rotating rod, creating either a single fibre or a continuous aligned film. The researchers were also able to control the proportions of multiwalled and single-walled nanotubes by altering the thiophene concentration and adjusting the hydrogen flow rate. Multiwalled nanotubes formed for a thiophene concentration of 1.5 to 4 wt% in ethanol, a hydrogen flow rate of 400-800 ml/min and a synthesis temperature of 1100-1180 °C. Single-walled nanotubes, on the other hand, formed when the thiophene concentration was around 0.5 wt%, the hydrogen flow rate was about 1200 ml/min and the temperature was up to 1200 °C.

The multiwalled nanotubes were about 30 nm in diameter and roughly 30 µm long, while the single-walled tubes had diameters of 1.6-3.5 nm and were grouped into bundles about 30 nm across. Windle and colleagues also coated a square-shaped wire frame with an aligned nanotube film by rotating it normal to the furnace axis. Then they infiltrated the nanotubes with a resin, making a composite shell that they were able to remove from the wire former.

""The present direct spinning process opens a novel way of one-step production of nanotube fibres, ribbons and coatings with potentially excellent properties and wide range applications”, said Windle.

Windle hopes that by tweaking the reaction conditions, characteristics such as strength and electrical conductivity can be improved. If the tiny tubes can be better aligned, the resulting fibres will be much stronger. Once refined, the authors note that ""if this new fibre can challenge conventional high-performance fibre for properties, its vastly simpler method of production will commend it on both cost and environmental grounds.""

Now, Windle and colleagues plan to collaborate with industry to scale up the process and develop materials applications. They also want to optimize the synthesis and properties of the product, as well as improving their basic understanding of the rapid synthesis reaction.