  Fibres of ultralong and aligned carbon nanotubes (CNT) have axial properties
above reference engineering materials, proving to be exceptional materials for
application in structural composites, energy storage and other devices. For CNT
fibres produced by direct spinning from floating catalyst chemical vapor
deposition (FCCVD), a scaled-up method, the challenge is to simultaneously
achieve high process conversion and high-performance properties. This work
presents a parametric study of the CNT fibre spinning process by establishing
the relation between synthesis conditions, molecular composition (i.e. CNT
type), fibre mechanical and electrical properties, and conversion. It
demonstrates tensile properties (strength 2.1 N/tex, modulus 107 N/tex) above
some carbon fibres, combined with carbon conversion about 5%, significantly
above literature on similar materials. The combined improvement in conversion
and properties is obtained by conducing the reaction at high temperature (1300
{\deg}C), using toluene as a carbon source, and through adjustment of the
promotor to carbon ratio (S/C) to favor formation of few-layer, collapsed CNTs
that maximize packing at relatively high conversions. Lower S/C ratios produce
low-defect single-wall CNT, but weaker fibres. An increase in electrical
conductivity to 3 x 10^5 S/m is also observed, with the data suggesting a
correlation with longitudinal modulus.
