Page 162 - Carbon Nanotube Fibres and Yarns

Carbon nanotube yarn structures and properties 153

Cho et al. [32] reported that CNT alignment can be improved by wet
stretching of NMP- and CSA-infiltrated solvent densified CNT yarns. The
SEM images of the CNT yarn surface in Fig. 7.14 show that the alignment
of the main CNT bundles improved with increasing stretch ratio. However,
there was no compelling evidence that CNT drafting was achieved as the
stretch applied was quite small (up to 17%) compared with the draw ratio
used in drafting staple fiber strands and drawing polymer filaments.
In the direct spinning method based on the floating catalyst CVD pro-
cess (detailed in Chapter 3), CNTs grown in a gas phase assemble into an

Fig. 7.14 SEM images of surface morphology of CNT fibers: (A) pristine, (B) NMP 0%, (C)
NMP 7%, (D) CSA 0%, (E) CSA 7%, and (F) CSA 13%. Scale bars: 500 nm [32]. (Reprinted
with permission from H. Cho, H. Lee, E. Oh, S.-H. Lee, J. Park, H.J. Park, et al., Hierarchical
structure of carbon nanotube fibers, and the change of structure during densification by wet
stretching, Carbon 136 (2018) 409–416.)