Production, structure and properties of twistless carbon nanotube yarns with a high density sheath

Carbon nanotube web drawn from a vertically aligned carbon nanotube forest is converted into a twistless yarn by a rubbing roller system. The yarn consists of a high packing density sheath with carbon nanotubes lying straight and parallel to the yarn axis and a low density core with many microscopic voids. The rubbing motion causes carbon nanotubes in the surface layers of the yarn to move in opposite directions and consequently large shear strains in the intermediate region tear the partially densified carbon nanotube assembly apart, resulting in the formation of large voids in the yarn core. The specific tensile modulus and sonic velocity of the core-sheath structured, twistless carbon nanotube yarns are significantly higher than that of their corresponding twist-densified yarns. These improvements have been attributed to increased nanotube-to-nanotube contact length in the high packing density sheath and very few carbon nanotubes lying at an angle to the yarn axis.