Carbon nanotubes have been highly studied by materials scientists who see the potential in their amazing stiffness, strength, thermal conductivity, electrical properties and high surface area. However, CNTs have yet to make significant impacts in products produced by the textile industry. But this could change, as new methods to produce high aspect ratio carbon nanotubes, and nonwoven fabrics directly from them, are emerging.
What are carbon nanotubes and how are they currently used in the textile industry?
Carbon nanotubes are tubular fibrous structures composed entirely of graphitic carbon planes. The carbon-carbon bonds form a hexagon shape within the lamellar graphite planes that resembles common chicken wire. A common analogy to describe the structure of a CNT is to picture the same sheet of chicken wire rolled up into a cylinder. The orientation of the graphite planes, parallel to the fiber axis, along with the seamless nature of the tube structure, enables their extreme mechanical properties. The diameter of carbon nanotubes can vary, usually from 1-50 nanometers, which is significantly smaller than fibers produced by meltblowing or optimized electrospinning processes.
Dry CNT fabric formation processes
One major requirement for producing fabrics directly from CNTs is that the CNTs should have an extremely high aspect ratio. CNT lengths in the range of hundreds of microns to millimeters should be used. While this length would be considered very short in the case of traditional staple textile fibers, in this case the nanoscale CNT diameter means the aspect ratios are in the hundreds of thousands. This is important because the surface of CNTs are smooth with no chemical functional groups, so the fabrics made from them are held together by the weak secondary interactions among tubes. Increasing the length of the CNTs allows for more of these interactions to “add up” along their length to allow for the creation of stable fabrics.
Where it could lead
Fabrics made entirely of carbon nanotubes have many potential applications. One of the most attractive is in high-strength composite materials. Fabrics with long, aligned, individualized CNTs can be used to produce resin pre-impregnated fabrics and high-fiber volume fraction composite materials with morphologies that resemble traditional carbon fiber materials.
With the multifunctional properties they would provide, CNT fabrics and composites produced from them may fill needs not met by carbon fiber composites in defense, aerospace, automotive and consumer markets. Their high specific surface area, chemical stability and thermal stability make them a great candidate for battery electrodes, catalyst supports, thermoelectric materials, and air and water filtration.
