Page 58 - Carbon Nanotube Fibres and Yarns

50 Carbon Nanotube Fibers and Yarns

(A) (B)

(C)

Fig. 3.10 CNT fiber produced by different spinning methods. (A) Direct spinning. (B)
Bath spinning. (C) Rotating anchor spinning. (Panel (A) reproduced with permission from
Gspann TS, Juckes SM, Niven JF, Johnson MB, Elliott JA, White MA, et al. High thermal con-
ductivities of carbon nanotube films and micro-fibres and their dependence on morphol-
ogy. Carbon 114 (2016) 160–168, (B) from Zhong XH, Li YL, Liu YK, Qiao XH, Feng Y, Liang
J, et al. Continuous multilayered carbon nanotube yarns. Adv. Mater. 22 (2010) 692–696,
and (C) from Schauer MW, White MA. Tailoring industrial scale CNT production to specialty
markets. MRS Proceedings 2015;1752:mrsf14-1752-mm04-07.)

The nanoscale CNTs usually self-assemble into mesoscale bundles,
which are the bridging units for forming the macroscopic fiber and sheet.
Directly correlating the structure of the nanoscale CNTs with the proper-
ties of macroscopic fiber and sheet is challenging. In one study the CNT
fiber tensile strength was found not dependent on the individual CNT di-
ameter and wall number [48], probably due to the dominant effect of CNT
bundle length on load bearing instead of the diameter of individual CNTs.
Thus for assessing the properties of CNT macroscopic entities, the proper-
ties of the CNT bundles, instead of individual CNTs, are used. It has been
suggested that few-layer larger diameter CNTs can autocollapse under cer-
tain conditions, which increases the contact area and load transfer between
nanotubes, and thus improves bundle strength [52, 61]. It is widely accepted
that longer CNTs or bundles could increase the strength and elongation at
break [61, 62]. Chapters 7 and 8 provide detailed discussions on the struc-
tural mechanics of CNT fibers.