Page 97 - Carbon Nanotube Fibres and Yarns

Carbon nanotube-reinforced polymer nanocomposite fibers 89

12 μm, respectively. CNTs have also been used as surface modifier for car-
bon fibers to reinforce the interfacial stress transfer between the carbon fibers
and the matrixes, leading to improvements to interface adhesion, interfacial
strength, and in-plane shear strength of the resulting composites [68].

5.3.2 PVA fiber
PVA crystal has a planar zig-zag structure similar to that of PE. The theoretical
modulus of PVA fiber is as high as 250–300 GPa. Kuraray uses a gel spin-
ning technique to produce high-performance PVA fibers with excellent ten-
sile properties (tensile modulus: 11–43 GPa, tensile strength: 0.9–1.9 GPa) and
high alkali resistance. CNTs show strong nucleate and templating effects on
PVA crystals [23, 30, 69] and can be used to reinforce PVA fibers. Zhang et al.
found that by the addition of 3 wt% CNTs, the tensile strength and modulus of
gel-spun PVA fibers increased from 0.9 to 1.1 GPa and from 25.6 to 35.8 GPa,
respectively [44b]. Miaudet et al. added 0.35 wt% of SWNT in wet-spun PVA
fibers and found that the tensile modulus increased from 2.5 to 14.5 GPa and
the strength increased from 0.6 to 1.6 GPa [70]. Xu et al. dispersed 0.3 wt% of
SWNT into gel-spun PVA fibers and found that the tensile modulus was im-
proved from 28 to 36 GPa and the strength from 1.7 to 2.2 GPa [71]. Dai et al.
used 0.6 wt% tea polyphenol-functionalized MWNT to reinforce PVA fibers
and observed a strength improvement of more than 160% [72]. Zhou et al.
prepared PVA composite fibers with 20 wt% MWNT and obtained a high
−3
modulus of 41.5 GPa and an electrical conductivity of 6.85 × 10 S/m [73].
Minus et al. attempted to optimize gel spinning and drawing parameters [30].
When the fiber was finally drawn at 290°C, the modulus and strength of the
PVA fiber reached as high as 48 and 1.6 GPa, respectively. Under the same
spinning and drawing conditions, 1 wt% SWNT/PVA fiber showed a modulus
of 71 GPa and a strength of 2.6 GPa. In a later study, Minus et al. used steady
shear flow gel-spinning method to produce a PVA/SWNT nanocomposite
fiber with tensile strength, modulus, and toughness of 4.9 GPa, 128 GPa, and
202 J/g, respectively, which are the highest reported values up till now [74].
The key factor for the excellent reinforcement of CNTs on PVA fibers is the
development of highly crystallized and oriented interphase structures.

5.3.3 Aromatic fiber
Poly(p-phenylene benzobisoxazole) (PBO) is a rigid-rod polymer [75].
PBO fiber has high tensile strength, stiffness, and thermal stability. A PBO
fiber was commercialized by Toyobo Co. (Japan) in 1998 with the trade
name Zylon. PBO exhibits lyotropic liquid crystalline behavior similar to