Page 36 - Carbon Nanotube Fibres and Yarns

Yarn production from carbon nanotube forests 29

Aligned MWCNT array 11.1

Die f 1.58 30° 38 2.5
f 0.76
CNT yarn
CNT sheet
Si wafer substrate Material: Al 2 O 3
Fig. 2.12 Producing dry-spun CNT yarns by drawing CNT webs through a narrow die:
(I) schematic of the process and (II) geometry of the die [44]. (Reprinted with permission
from 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.)

large capillary force (Δp=γ/r, where γ is the surface tension of the liquid
and r is the distance between adjacent tubes). This phenomena was used
to densificate a CNT web into a compact yarn of irregular cross section
by passing through a droplet of ethanol or other types of volatile liquids
(Fig. 2.13) [8]. A well-rounded yarn cross section can be produced by using
an additional twisting operation [46, 47]. Liquids can also be introduced to
the yarn forming point in the flyer and up-spinning machines described
earlier to achieve simultaneous liquid densification and twist densification.

Fig. 2.13 CNT yarn production by liquid densification: (A) spinning a continuous yarn
from vertically aligned CNT arrays, (B) two yarns merging into one tight fiber after pass-
ing through an ethanol droplet, and (C) schematic illustration of processing yarn in
ethanol, showing the pinch effect of the meniscus [8]. (Reprinted with permission from
X. Zhang, K. Jiang, C. Feng, P. Liu, L. Zhang, J. Kong, et al., Spinning and processing continu-
ous yarns from 4-Inch wafer scale super-aligned carbon nanotube arrays, Adv. Mater. 18 (12)
(2006) 1505–1510.)