Researchers in US have produced electrically conducting yarns from bundle of carbon nanotubes and various powders and nanofibres. The yarns are made by a technique called biscrolling. The yarns are very strong and can be woven, sewn, knitted and braided into a variety of structures. They could find applications in energy storage and harvesting, structural composites, photo catalysis and intelligent textiles.

Current methods to transform powders with useful properties into yarns involve using polymer binders to fix the powders in place. The problem is that the resulting composites are not very strong and the desirable properties of the powder usually degrade during processing. CNT sheets are ideal for making such yarns because they are very light, stronger than steel and can be easily washed.

Researchers at the Nanotech Institute at University of Texas in Dallas have developed a new method of making electrically conducting, sturdy yarns using carbon nanotube (CNT) sheets, or webs, instead of polymers to transform nano- or micron-sized powders.

Technique

The technique is similar to conventional textile-spinning methods. In the developed process, CNT sheets are overlayed with selected powders using an electrostatic powder-coating gun and then twist-spinning the stack to form a biscrolled yarn of 10 nm diameter made of multiwalled carbon nanotubes deposited on a substrate while applying a twist at the same time. Structures of different shapes can be produced and can be made from a variety of powders for various final applications. By this method superconducting yarn has been made by biscrolling a mixture of magnesium and boron powders (up to 99 wt %) as the guest on CNT sheets, and then thermally annealing the biscrolled yarn.

Applications

The biscrolled yarns can be made from a variety of powders that can be chosen according to the final application. The technique avoids the 30 or more drawing steps needed in conventional powder-in-tube methods to produce millimetre-sized, iron-clad, superconducting wires from a magnesium/boron/CNT precursor. The yarn has a high gravimetric electrical conductivity, highly flexible and mechanically robust and hence could be used in applications like energy storage devices such as for lighter batteries and energy-generating clothing textiles called intelligent textiles. These yarns could be used for making weavable anodes for flexible lithium-ion batteries, electrodes for lithium-ion batteries using environmentally friendly LiFePO4, highly catalytic fuel cell cathodes using nitrogen-doped carbon nanotubes which can avoid expensive platinum.