Page 103 - Carbon Nanotube Fibres and Yarns

Carbon nanotube-reinforced polymer nanocomposite fibers 95

perfect SWNT with a strength greater than 140 GPa, the R c is extremely
high. As discussed earlier, as CNT aspect ratio increases, it becomes more
and more difficult to disperse individual CNTs uniformly in the nanocom-
posites. On the other hand, a higher τ c leads to a lower R c . The formation of
interphase between the CNT and the polymer matrix improves the stress
transfer and the interfacial strength (τ c ). Different CNT surface chemical
modification treatments have been designed to improve CNT dispersion
and the interfacial stress transfer in nanocomposites [88]. However, the ex-
istence of CNT surface functional groups, surfactant and interface compat-
ibilizer can also adversely affect the formation of highly ordered interphase
structures.
In summary, the CNT length, dispersion, orientation, and interfacial
shear strength are key factors for the mechanical performances of nanocom-
posite fibers. These factors can work against each other. For example, a high
CNT aspect ratio is preferred for interfacial stress transfer, but it makes the
dispersion of CNTs in the nanocomposites extremely difficult.

5.5 Perspective
Due to the large surface area and 1D rod structure, CNTs are a preferred
reinforcement material for polymer fibers. Incorporating CNTs in poly-
mers has been found to improve the tensile properties of almost all fibers,
including but not limited to PE, PP, PVA, PC, polymethyl methacrylate,
PBO, cellulose, PAN, and its derived carbon fibers. CNTs act as nucleating
agent for polymer crystallization and template for polymer orientation.
In a CNT-reinforced nanocomposite fiber, the reinforcement of tensile
property comes not only from the superior properties of CNTs, but also
from the formation of highly ordered interphase polymer structures in
many cases.
The first-generation nanocomposite fibers are based on the full utiliza-
tion of the excellent properties of the nano-fillers as well as the dispersion,
orientation, and interfacial shear strength of the nano-fillers in the polymer
matrixes. Beside tensile properties, the addition of CNTs in polymeric fi-
bers can also improve other properties of the composite fibers, including
electrical and thermal conductivity. By adjusting the type of CNTs as well
as their concentrations and orientations, electrical and thermal conductivity
can be improved and tailored for different applications. The electrical and
thermal conductivity of CNT/polymer nanocomposite fibers can be fur-
ther tuned during the fiber extrusion and drawing stages.