A Review of Conductive Cotton Fabric - Smart Textiles

Introduction
Over the past decade, the remarkable effort has been put into the development of smart textiles (e-textiles), which generally are fabricated by integrating electrical circuits into traditional textiles to modify their functionalities. Generally speaking, these textiles are defined as “smart” because they have the functions that enable them to directly respond to environmental stimuli, such as mechanical, thermal, chemical, electrical, and magnetic.
Potential applications of smart textiles may include wearable computing fabrics, antistatic & electromagnetic shielding garments data transfer within thermal sensing on tactile features for medical and athletic applications.

To realize the “smart” functions of a textile, conductive textile yarns or fibers are generally used to interface with other electronic devices integrated into the textile. Many of the conductive yarns used in the current generation of smart textiles are fabricated from metal yarns/fibers made from copper, stainless steel (SS), silver, brass nickel, and their alloys (swicofil, n.d.a). These metallic yarns, though featuring relatively high electrical conductivities, are generally heavier and stiffer than commercial textile yarns based on polymer materials such as nylon, wool, and cotton.

The flexible conductive cotton fabric could be made by the coating of Carbon nanotubes (CNT) in the outer surface of cotton material. In this article coating of cotton by CNT will be described in the yarn and fabric state. the mechanical properties of the fabric are improved by the CNTs coating and imparted conductivity to the fabric. Strain sensors made from the CNT cotton fabric (CCF) exhibited a large workable strain range (0~100%), fast response, and great stability. CCF-based strain sensors could be used to monitor the real-time human motions (Mengyun, et al).

Carbon nanotubes (CNTs)
Carbon nanotubes are long, thin cylinders of carbon were discovered in 1991 by the Japanese scientist Sumio Iijima. These are large macromolecules and are unique for their size, shape, and remarkable physical properties. Depending on the number of carbon layers, a distinction is made between single-walled (SWNT) and multi-walled carbon nanotubes (MWNT). They are usually made by carbon-arc discharge, laser ablation of carbon, or chemical vapor deposition. Their diameter may vary between 0.4 and several nanometers; their length may be several hundred microns. They are 100 times stronger than steel while weighing six times less, and being one giant molecule, carbon nanotubes have unusual and extraordinarily good mechanical, electrical, and thermal properties.

Fig: (a) single-walled (SWNT) and (b) Multi-walled carbon nanotube (MWNT).
(courtesy: www.pa.msu.edu/cmp/ntproperties, April 12, 2009 )

CNT coated Conductive cotton fabric making process:
1. Fabric coating: There are several methods to apply CNTs in the cotton fabric surface. (Mengyun, et al) Shows a process of coating of cotton fabric for motion sensing and heating application.
The CNT-cotton fabric (CCF) could be prepared by a “dip-and-dry” method.
Soaking of elastic knitted cotton fabric in ethanol for 30 min and then washed thoroughly with deionized water. A stable CNT suspension could be obtained through dispersing the CNTs in water followed by 15 min sonication at room temperature. The cotton fabric sample should be immersed in CNT suspension with different concentrations and kept in solution for 20 min at room temperature under sonication. Then fabric should be dried in an oven at 40 °C. Different cycles of “dip-and-dry” were performed to obtain the required level of coating on cotton fabric CCF.

2. Yarn coating: It is very difficult to coat in yarn state. Some extra process should be followed to make the yarn weave able in the industrial loom. To solve this problem yarn made in a vary finer appearance then CNT coating is applied in the yarn surface. The industrial loom is used to make fabric. To get the desired effect Jacquard loom could be used to make the required design.

Fig: (a) Conductive yarn (b) Jacquard weaving (c) woven conductive fabric
(courtesy: Project Jacquard, Google ATAP) 

Application:
The main advantage of conductive textile is flexibility. Flexible conductive materials have attracted considerable attention from the researchers recently due to their potential applications in Smart Textiles especially wearable displays, flexible touchscreen, electronic sensors for human motion, and electrically driven heaters.

Fig: Military uniform with wearable computer and keyboard.

Photo source: www.fastcompany.com/1552679/body-electric-britain-win-hearts-minds-powered-militaryuniforms, https://www.pinterest.com/ingose/e-textile

CNT- cotton fabric based strain sensors could be used to monitor the real-time human motions, such as standing, walking, running, squatting, and bending of finger and elbow.

Bibliography:
Mengyun, Y., Junjie, P., Anchang , X., Lei, L., Deshan, C., Guangiming, C., . . . Xungia , W. (n.d.). Conductive Cotton Fabrics for Motion Sensing and Heating Applications.
Project Jacquard, google ATAP. (n.d.).
Suh, M. (2015). Wearable sensors for athletes. Elsevier Ltd. Retrieved from Electronic Textiles. http://dx.doi.org/10.1016/B978-0-08-100201-8.00013-8
Uddin, A. J. (n.d.). Coating of Technical Textile Yarn. Woodhead publishing limited.
1. www.fastcompany.com/1552679/body-electric-britain-win-hearts-minds-powered-militaryuniforms
2.  https://www.pinterest.com/ingose/e-textile
3. www.csiro.au
 

Abdullah Al Mansur
Department of Fabric Engineering, 
Textile Engineering College, Noakhali.