Page 111 - Carbon Nanotube Fibres and Yarns

P. 111

CHAPTER 6

Post-spinning treatments

to carbon nanotube fibers

Hai Minh Duong, Sandar Myo Myint, Thang Quyet Tran, Duyen Khac Le
National University of Singapore, Singapore, Singapore

Aligned CNT fibers can be fabricated by three methods: spinning from
CNT solution [1,2], spinning from CNT arrays [3–5], and direct spinning
via floating catalyst method [6–12]. The CNT fibers spun from the first two
methods are relatively clean, whereas the direct-spun CNT fibers contain
many impurities of catalyst and amorphous carbon due to their single-step
fabrication process [6, 13]. These residual impurities lower the fiber perfor-
mance and limit their applications. Although the as-spun CNT fibers pos-
sess excellent mechanical and electrical properties, many studies have been
conducted to further improve their properties by different posttreatments
[3, 14–21], such as densification treatments.
Densification treatments can be classified into indirect methods (such
as twisting [22,23], liquid densification [23], and drawing through dies
[24]) and direct methods (such as rubbing [25] and pressurized rolling
[26]). The indirect approaches are limited by their low densifying forces
[22–24], whereas the direct approaches are more effective as higher den-
sifying forces can be applied directly to the CNT fibers, resulting in
much denser CNT fiber structures [26]. CNT fiber properties can also be
enhanced by polymer infiltration, in which the formation of cross-links
between the CNT bundles through the infiltration process can effec-
tively improve the inter-tube load transfer efficiency of the CNT fibers,
resulting in their better mechanical performance [22, 27, 28]. Although
many studies have investigated the effects of each posttreatment on the
properties of CNT fibers, few researchers have reported their com-
bined effects [28–31]. Since each treatment has specific positive effects
on the properties of CNT fibers, the combination of two posttreat-
ment methods may be expected to improve the fiber performance more

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