Search

The effect of twist and solvent densification on the internal structure of carbon nanotube yarns was revealed using focused ion beam milling and related to yarn strength through tensile testing. Denser carbon nanotube yarns with smaller diameters were produced either through solvent densification or with increasing twist densities from 5 to ∼15 turns/mm, but led to only minor improvement in yarn tenacity. At twist densities greater than ∼15 turns/mm, a core-sheath structure developed and was correlated with a decline in strength. The implications of bonding between the nanotubes in the twisted yarn are briefly considered. These results have implications for the future development of high strength carbon nanotube yarn.

The efficacy with which a range of nanotubes could reinforce a high density polyethylene (HDPE) matrix was investigated, in relation to nanotube diameter, purity, functionalization, alignment and nanotube bulk density. Composites were prepared by melt blending multiwall carbon nanotubes (MWNTs) with high density polyethylene (HDPE), followed by the injection molding of tensile specimens. At a 5 wt% loading, the most effective nanotubes were those of large diameter, received in an aligned form with low bulk density, producing a 66% increase in elastic modulus and a 69% improvement in yield stress. This was contradictory to theoretical mechanics calculations that predicted an increasing degree of reinforcement for nanotubes of reduced diameter. This difference was explained by the higher degree of dispersion observed in the composites with MWNTs of greater diameter.

Carbon nanotubes (CNTs) have a range of useful properties, such as high strength and modulus, high electrical and thermal conductivities, are stable at relatively high and low temperatures, and because of a low density, the specific properties are even better. For these reasons, CNTs are of great technological interest, however, difficulties in assembling the trillions of nanotubes into macro-sized objects without the use of binders has retarded the growth of practical applications. The work presented outlines efforts to develop a solid-state process for nanotube assembly that promises to eliminate the requirement to use binders and capture the inherent properties of nanotubes. These processes include spinning CNT forests into yarns having toughness and high electrical conductivity, and drawing the forests to form webs with gravimetric strengths higher than high tensile steel plate. Both yarns and webs have high electrical conductivities and can be used for emission of light by incandescence.