Strength and Electrical Conductivity of Carbon Nanotube Yarns
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Strength and Electrical Conductivity of Carbon Nanotube Yarns Mark W. Schauer1, David S. Lashmore1, Diana J. Lewis1, Benjamin M. Lewis1, and Erick C. Towle1 1
Nanocomp Technologies, 162 Pembroke Rd, Concord, NH 03301, U.S.A. ABSTRACT The strength and electrical conductivity of Carbon Nanotube (CNT) yarns is dramatically affected by the handling of the material after the nanotubes are produced. Our nanotube production process involving Chemical Vapor Deposition (CVD) using the floating catalyst method produces a mass of entangled bundles of single-walled nanotubes in a gas suspension. Simply collecting and spinning this material produces a yarn with strength and electrical conductivity far less than the properties of the individual nanotubes due to the poor alignment of the bundles on the microscopic scale. We have developed methods of aligning the CNT material that are analogous to the techniques used in the textile industry for spinning staple yarns, but modified to be appropriate for nano-scale material. The result is a dramatic improvement in strength and electrical conductivity of our CNT yarns. INTRODUCTION The process to synthesize carbon nanotube (CNT) yarns and non-woven textiles by chemical vapor deposition (CVD) using a floating iron catalyst method is described. This process uses ferrocene, thiophene and ethanol and is similar to that used by others.1-7 The CNT material can be collected on a moving drum or belt to make non-woven textiles, or collected as a roving, and then processed into a yarn. Parameters associated with the injector and furnace control the length and diameter of individual nanotubes.8 Smaller diameter single-walled CNT’s will bundle in the furnace forming a staple fiber potentially longer than the individual tubes. The length of the nanotubes, as well as the bundles, affects the strength and electrical conductivity. However, the treatment of the material after nanotube growth has stopped also impacts material properties. The strength and electrical conductivity of the finished product depends not only on the length and diameter of the nanotubes, but also on bundle alignment. Parameters associated with these processes can be varied to optimize the strength and electrical conductivity of the resulting CNT yarn. In this paper the methodology of the yarn collection and processing is described. In our process the CNT material exits the furnace as dispersed webbing and then impinges on an anchor. Applying adjustable tension while the nanotubes are in this highly dispersed state as they are being pulled from the anchor is particularly effective at aligning the tube bundles. Once the material is collected onto a spool, as a roving, it can be processed to further improve alignment by immersing in a lubricant and pulling through a roller stretcher. The alignment imparted by careful stretching of the material, both in the collection of the roving and post processing, greatly enhances yarn strength and electrical conductivity. Strength can be further enhanced by adding a polymer matri
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