Page 173 - Carbon Nanotube Fibres and Yarns

164 Carbon Nanotube Fibers and Yarns

70 100
Twisted yarns
60 80 False-twisted yarns
Tenacity (cN/tex) 40 Tenacity (cN/tex) 60
50
30
40
20
10 20
0 0
0.1 0.3 0.5 0.7 0.9 1.1 1.3 0.1 0.2 0.3 0.4 0.5 0.6 0.7
(A) Yarn density (g/cm ) (B) Yarn density (g/cm )
3
3
100 Cold-drawn yarns 250 Solvent densified yarns
Tenacity (cN/tex) 80 Tenacity (cN/tex) 150
200
60
100
40
20 50
0
0
0.4 0.6 0.8 1 1.2 1.4 0.2 0.3 0.4 0.5 0.6 0.7 0.8
3
(C) Yarn density (g/cm ) (D) Yarn density (g/cm )
3
Fig. 7.19 Relationship between yarn density and tenacity. (A) Twisted yarns, calculated
based on the data from Ref. [14], (B) false-twisted yarns, calculated based on the data
from Ref. [6], (C) cold-drawn yarns, calculated based on the data from Ref. [30], and (D)
solvent-densified yarns, calculated based on the data from Ref. [32]. (Source of (A): M.
Miao, J. McDonnell, L. Vuckovic, S.C. Hawkins, Poisson’s ratio and porosity of carbon nano-
tube dry-spun yarns, Carbon 48 (10) (2010) 2802–2811. Source of (B): M. Miao, The role
of twist in dry spun carbon nanotube yarns, Carbon 96 (2016) 819–826. Source of (C): K.
Sugano, M. Kurata, H. Kawada, Evaluation of mechanical properties of untwisted carbon
nanotube yarn for application to composite materials, Carbon 78 (2014) 356–365. Source
of (D): 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.)

By adjusting the diameter of the die, cold-drawn CNT yarns can achieve
similar levels of density as that obtained by twist insertion. The reported
3
yarn tenacity achieved at 1.1–1.2 g/cm (Fig. 7.19C) is similar to that of the
3
twisted yarn at its optimum density of about 0.6 g/cm (Fig. 7.19A).
Solvent-densified twistless yarns normally do not have regular cross
sections and therefore, the yarn density is rarely reported. Cho et al. [32]
presented results of NMP and CSA treated yarns subjected to stretching, as
plotted in Fig. 7.19D. The reported yarn density was rather low (similar to
the false-twisted yarns in Fig. 7.19B), but the yarn tenacity was very high.
The dramatic improvement of yarn tenacity was attributed to the increased
nanotube bundle size, bundle compaction, and alignment [32].