Page 119 - Carbon Nanotube Fibres and Yarns

Post-spinning treatments to carbon nanotube fibers 111

in strength after a 2-h treatment. However, too long acidization time could
destroy the crystalline structure of the CNTs, leading to a decrease in the
fiber strength.
Fig. 6.3 compares the surface morphologies, and mechanical and elec-
trical properties of the as-spun and purified CNT fibers. The as-spun CNT
fibers in Fig. 6.3A and B consisted of aligned CNT bundles along the
fiber axis and their diameters were about 8 ± 0.2 μm. Due to the impurity
removal after the purification treatment, the fiber diameter was reduced
by nearly 19%, reaching 6.5 ± 0.18 μm (Fig. 6.3C). The good alignment
of CNT bundles observed in the structure of the purified CNT fibers
(Fig. 6.3D) suggests that the purification treatment preserved the fiber
structure. Additionally, the larger bundle size observed in Fig. 6.3D suggests
the positive effects of the purification treatment on the impurity removal,
leading to stronger van der Waals interactions between the CNTs and CNT

(A) 10µm (B) 2µm

(C) 10µm (D) 2µm

0.4 4679
Purified CNT fiber As-spun fibers
As-spun CNT fiber Purified fibers
0.3
Strength (GPa) 0.2 20.66 2369

0.1 8.41
0.32 0.38
0.0
0.00 0.04 0.08 0.12 0.16 Strength Young’s modulus Electrical conductivity
Strain (GPa) (GPa) (S/cm)
(E) (F)
Fig. 6.3 SEM images of (A, B) as-spun CNT fiber and (C, D) purified CNT fiber, (E) stress-
strain curves, and (F) mechanical and electrical properties of the as-spun and purified
CNT fibers.