Page 144 - Carbon Nanotube Fibres and Yarns

P. 144

CHAPTER 7

Carbon nanotube yarn structures

and properties

Menghe Miao
CSIRO Manufacturing, Geelong, VIC, Australia

Carbon nanotubes (CNTs) have been shown to possess extraordinarily high
mechanical properties [1, 2] combined with good electrical and thermal
conductivity [3]. The challenge is to organize these nano-sized building
blocks into macroscale structures that express similar properties. Without
considering their detailed atomic structures, CNTs can be considered as
nanoscale fibers that resemble the diameter of fibrils in plant and animal
fibers such as cotton and wool. It is, therefore, a logical approach to align the
CNTs in the form of a fiber or yarn that is expected to outperform their
conventional textile counterparts [4].

7.1 CNT yarn geometry

7.1.1 Twist
Twist insertion has been an important method to densify CNT webs drawn
from vertically aligned CNT arrays (CNT forests) since it was first reported in
2004 [5]. The method imitates the spinning of short textile fibers (staple fibers)
into a continuous yarn, which has been traditionally used and is still the pre-
dominant method of staple fiber yarn production in the textile industry today.
Twist is applied to a yarn by rotating one end of the yarn while it is
wound on a bobbin. In the textile industry, twist is measured by counting
the number of turns required per unit length (T, turns per unit length) to
cancel out the twist applied to the yarn during spinning. In spinning mills,
the twist applied to a yarn is set by tuning the ratio between the rotational
speed of the spindle (revolutions per minute) and the throughput speed of
the yarn (length per minute) set on the spinning machine.
The geometry of twisted yarns is often represented by a series of coaxial
helices (Fig. 7.1), a model first proposed by Gégauff in 1907 [7]. The model has
been widely adopted, sometimes with minor modifications, in yarn structural

139 140 141 142 143 144 145 146 147 148 149