Page 40 - Carbon Nanotube Fibres and Yarns

Yarn production from carbon nanotube forests 33

Fig. 2.16 Flexibility of the SS substrate before and after thermal CVD CNT forest
growth: (A) an SS foil bent on the inner surface of the quartz tube (inner diameter,
ca. 65 mm) used as a reactor chamber before being submitted to the CVD thermal pro-
cess. (B) Piece of a forest growth on an SS foil being elastically bent. (C) Photograph
of a 5-cm-wide CNT sheet being pulled from a forest growth on a bent SS substrate
[50]. (Reprinted with permission from X. Lepró, M.D. Lima, R.H. Baughman, Spinnable car-
bon nanotube forests grown on thin, flexible metallic substrates, Carbon 48 (12) (2010)
3621–3627.)

studied drawability of CNT forests using experimental and modeling tech-
niques. With improvements made on synthesis techniques, drawable CNTs
can now be grown to several millimeters long. The speed of drawing a web
from CNT forests, which sets the upper limit for instantaneous yarn pro-
ductivity, can be very high, up to almost 1000 m/min.
The webs drawn from CNT forests can be converted into continuous
yarns by several methods, including twist insertion (spinning), false-twisting,
mechanical rubbing, die-drawing, and solvent densification. Automation of
the spinning operation, forest joining, and continuous synthesis of CNT
forest on flexible substrate are some of the methods proposed for commer-
cial scale production of continuous yarns. The twist insertion rate for CNT
yarn production can be scaled up to the level comparable to state-of-the-art
fine count conventional textile yarn production using specially engineered
spinning machinery or modified conventional textile machinery. Higher
speed methods of yarn densification have also been experimented, includ-
ing mechanical rubbing, die-drawing, and solvent densification.