Page 76 - Carbon Nanotube Fibres and Yarns

68 Carbon Nanotube Fibers and Yarns

room temperature. An average thermal conductivity of 380±15 W/m K was
measured on ~1.5-mm-long samples using a 3-omega method. Doping
by iodine increased the electrical conductivity to 5±0.5 MS/m (resistivity
22±4 μohm cm) and the thermal conductivity to 635 W/m K.

4.4 Alternative wet-spinning route

Zhang et al. [15] reported a wet-spinning method to produce pure MWNT
fibers using ethylene glycol instead of superacid. Ethylene glycol is used
industrially as a raw material in the manufacture of polyester fibers. The
carbon nanotubes were dispersed in ethylene glycol to form liquid crys-
talline dispersions, which was followed by extrusion into a diethyl ether
bath. Upon entering the ether bath, the ethylene glycol rapidly diffuses
out of the extruded CNT fiber into the ether, with ether back-diffusing
into the fiber. The ether-swollen fibers were then heated at 280°C to re-
move any residual ethylene glycol. The nanotubes within these fibers were
found to be highly aligned due to the combination of shear forces and
the liquid-crystalline phase. The resulting MWNT fibers possessed a high
electrical conductivity of 80 S/cm, a Young’s modulus of 69±41 GPa and a
strength of 0.15±0.06 GPa, which were lower than those of the superacid
solution-spun fibers.

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