Page 128 - Carbon Nanotube Fibres and Yarns

120 Carbon Nanotube Fibers and Yarns

6.8 Hybrid treatments of CNT fibers
A hybrid posttreatment method consisting of acidization and epoxy infil-
tration was developed to enhance the mechanical performance of the CNT
fibers spun by the floating catalyst method. The treatment time for acidiza-
tion was optimized to balance between purification effects and structural
damage on the CNTs; whereas for the epoxy infiltration step, the concen-
tration of the epoxy solution was optimized to achieve high load transfer
efficiency between CNTs. This method was proposed to provide a strategy
to improve the multifunctional properties of as-spun CNT fibers, in partic-
ular, those produced by the floating catalyst method.
Many studies have reported the successful improvement of the inter-tube
interactions of CNT fibers by enhancing their van der Waals interactions
through densification [23, 26, 28, 61] and purification [31, 40, 62] or cre-
ating new cross-links between the CNTs through polymerization [22, 27,
28, 63]. Among these posttreatments, densification and polymer infiltration
are the most effective methods because they can result in the highest en-
hancement factor for the mechanical and electrical properties of the CNT
fibers [22, 26–28].
6.8.1 Combined purification and epoxy infiltration

The 15-min acidized CNT fibers mentioned before were used for the
epoxy infiltration treatment to further enhance their mechanical proper-
ties. Since the epoxy viscosity was high (up to 17 mPa s), a set of diluted
epoxy solutions in acetone (10, 20, 30, 40, and 50 wt.%) were prepared to
study their infiltration effectiveness. Fig. 6.10A shows an SEM image of
the epoxy-infiltrated CNT fibers using 30 wt.% epoxy solution and the

10.83 µm

20µm
(A) (B)
Fig. 6.10 (A) SEM image of the CNT fibers after epoxy infiltration at 30 wt.% and (B)
effect of epoxy infiltration on diameter of the CNT fibers.