Page 82 - Carbon Nanotube Fibres and Yarns

Carbon nanotube-reinforced polymer nanocomposite fibers 75

Fig. 5.2 (A) SEM images of PE crystallized on CNT fiber via solution crystallization [19];
(B) cross-polarized optical images of PP transcrystalline layer formed on a single CNT
fiber [20a]; and (C) high-resolution images of an individual CNT coated with PC sheath
on fracture surface [21]. (Source of (A): S. Zhang, W. Lin, C.-P. Wong, D.G. Bucknall, S. Kumar,
Nanocomposites of carbon nanotube fibers prepared by polymer crystallization, ACS Appl.
Mater. Interfaces 2 (6) (2010) 1642–1647. Source of (B): S. Zhang, M.L. Minus, L. Zhu, C.-P.
Wong, S. Kumar, Polymer transcrystallinity induced by carbon nanotubes, Polymer 49 (5)
(2008) 1356–1364. Source of (C): W. Ding, A. Eitan, F.T. Fisher, X. Chen, D.A. Dikin, R. Andrews,
L.C. Brin son, L.S. Schadler, R.S. Ruoff, Direct observation of polymer sheathing in carbon
nanotube−polycarbonate composites, Nano Lett. 3 (11) (2003) 1593–1597.)

aerogel fiber were observed after solution crystallization (Fig. 5.2A) [19].
Zhang et al. reported the formation of ellipsoid-shaped PP particles that
were templated by CNT via controlled solution crystallization [22]. Even in
solution state under external shearing, CNT was found to template and align
PVA chains to form an oriented fibril structure; while self-assembled PVA is
totally randomly orientated [23]. The aligned CNT has also been observed
to retain polymer orientation during heating. In an oriented PET sample,
PET totally lost its orientation after melting and subsequent slow cooling;
whereas, PET remained oriented in CNT-containing sample under the same
heat treatment [24]. This is because the aligned CNTs help maintain PET
chain orientation even in melting and template its recrystallization during
cooling. The templating of polymer crystals by CNTs can be extended from
individual tube to nano-size bundle, and to macro-size fiber. After isothermal
crystallization, PP formed a transcrystalline layer on the surface of a CNT
fiber with a diameter of ~40 μm (Fig. 5.2B), while spherical PP crystals
formed in the neat matrix [20]. For fiber spinning, CNTs, which have 1D
geometry, can be easily aligned by shear flow. Through the templating ef-
fect of CNT, polymer orientation is expected to be improved. The presence
of CNT in polymeric fibers improves polymer orientation in comparison
to pristine polymer fiber spun under identical condition. For example, the