Page 92 - Carbon Nanotube Fibres and Yarns

Carbon nanotube-reinforced polymer nanocomposite fibers 85

CNT-reinforced polymeric fiber has been rarely reported. Highly oriented
CNTs and polymer chains as well as the existence of interphase improves
the thermal transportation from CNT to polymer in nanocomposite fibers,
and thus the enhancement of thermal conductivity by CNTs in an aniso-
tropic fiber is also greater than that in an isotropic nanocomposite. This is
an underexplored area and more works are needed.

5.3 Examples of high-performance CNT-reinforced
polymeric fibers
Over 3000 journal papers on the topic of CNT-reinforced polymers are
published each year. Even though many of these papers show improved
performances with the addition of CNTs in polymer matrices, practical
applications of CNTs in high-performance polymer fibers are still very rare.
The current fiber market is very cost sensitive. Unless CNT-reinforced fi-
bers offer superior performances than current products, the processing cost
of CNTs and nanocomposites could make the applications of CNTs unre-
alistic. Additionally, there are some huge technical barriers between labora-
tory scale samples and industrial products. The technology readiness levels
(TRLs) of these works are mostly between 1 and 3 (the proof of concept).
A TRL level of 5 or higher is required to reach the stage of technology
demonstration. The investment barrier to bridge this gap is high while there
is no guarantee of a successful outcome. In this section, we discuss the ad-
vancements of CNT-reinforced high-performance fibers with potential for
commercial utilization, including CNT-reinforced PAN-based carbon fiber,
PVA fiber, and aromatic fiber.

5.3.1 CNT-reinforced carbon fibers
Carbon fiber, with its high tensile properties and relatively low density, is
widely used as reinforcement in composite materials. Carbon fiber is made
from polymer fibers, predominantly PAN fiber. The structures and proper-
ties of the PAN precursor fiber strongly affect the quality of the resulting
carbon fiber. The traditional manufacturing methods for PAN precursor
fibers are wet spinning and dry-jet wet spinning, which give PAN precursor
fibers a strength of 0.4–0.6 GPa and a modulus of 8–12 GPa. Gel spinning
is a relatively new spinning technology used to produce high-performance
fibers [27, 62]. During gel-spinning, PAN polymer solution is gelled in a
cold methanol bath and the gelled fiber is further hot-drawn to a very high
draw ratio. Gel spinning was recently adopted for extrusion of PAN fibers.