are fibre spinning from CNTs in liquid solutions [21] and CNT fibre
drawing directly from gaseous CNTs produced by floating catalysts
[22]. Dry spinning is a third technique that consists in assembling
fibres from vertically aligned CNTs without any additional handling
steps in the process [23e25]. Basically, this corresponds to synthesizing
CNTs with unique density and length. In the dry spinning
process, Van der Waals interactions bind the CNTs together,
allowing the array to be continuously drawn. The main advantage
of this technique is the catalyst-free high alignment, and a smaller
diameter distribution of the CNTs within the thread [23,26].
Various researchers have addressed the strength vs. toughness
problem using CNT-based fibres. Dalton et al. produced composite
fibres from polyvinyl alcohol (PVA) and about 60% by
weight Single-Wall CNT (SWCNT), achieving a strength of 1.8 GPa
and toughness of 570 J/g [27]. The fibres produced in Ref. [28],
also based on PVA and SWCNT, reached an even higher value of
870 J/g, and the technique was also demonstrated for Multi-Wall
CNTs (MWCNT), although with reduced strength and toughness
values.
An approach to obtain artificial fibres that are simultaneously
strong and tough is to try to replicate the mechanisms that are
occurring at nano- micro- and macro-scale levels in natural