As 1D materials with high intrinsic strength and stiffness, nanotubes are promising building
blocks for the next generation of fibres in structural composites. This thesis explores wet
spinning techniques for assembling macroscale fibres from nanotubes. Carbon nanotubes
(CNTs) are an obvious target material to compete with commercial carbon fibres, based on
their excellent intrinsic mechanical properties and low density, alongside high electrical
conductivity for multifunctional applications. However, studying CNT materials is challenging
due to their intrinsically high optical absorbance and low X-ray scattering cross-section, as
well as the dispersity of typical feedstocks in both size and helicity. Imogolite nanotubes (INTs)
are an inorganic analogue that offers an opportunity to observe the assembly of nanotubes
into fibres using both polarised optical microscopy (POM) and X-ray scattering (XRS). In
contrast to CNTs, INTs are optically transparent and can be synthesised at low temperature
to provide feedstocks that are uniform in structure and diameter.
In this work, the first known pure INT fibres have been produced and used to understand the
nanotube wet spinning process. In situ POM demonstrated that in cylindrical spinnerets the
spinning dope undergoes plug flow with inhomogeneous alignment due to the shear thinning
nature of the solutions. The use of a tapered spinneret enables good alignment of the spinning
dope, due to the induced extensional flow. Using this information, CNT fibres were spun from
reduced CNT solutions and the wet spinning process was refined using a combination of in
situ observation and statistical experimental design. The dissolution of negatively-charged
CNTs (nanotubides) was examined both from a theoretical perspective and experimentally to
identify the key conditions required to obtain homogeneous spinning dopes. The optimal
dissolution depended upon both degree of charging and effective stirring. The optimised CNT
dope was then wet spun using a variety of coagulating systems to identify the accessible
process window and optimum parameters for spinning from these reactive charged solutions.
Further improvement of the CNT fibre properties is predicted to arise through the use of
higher aspect ratio CNT feedstocks. However, challenges still remain in the liquid phase
processing of longer CNTs. In order to create CNT fibres competitive with commercial CFs,
future research should focus on how to process these longer feedstocks following the
guidance in this thesis.Open Acces
