Research Bioengineers at the United States Army Soldier Systems Center in Natick, Massachusetts have recently developed fabrics that are embedded with nanofibers and hydrogel particles. Nanofiber clothing based on these fabrics have the potential to keep soldiers warm and comfortable when they are working in colder climates.
This work is based on research originally conducted at Stanford University in California, where the Researchers developed a cotton fabric embedded with a network of very fine silver nanowires that could heat up when electric power is supplied to the wires. The fabric made of nanofibers and hydrogels developed by Phil Gibson and Calvin Lee for military purposes was presented at the 254th National Meeting and Exposition of the American Chemical Society1.
If this concept is successfully translated into making thermal protective clothing for soldiers in colder environments, it could increase their mobility, as well as facilitate temperature adjustment on their clothing that is compatible with their specific environment.
Nanofibers are fibers with a diameter that measures less than 1 micrometer (µm). Due to their special properties, nanofibers are currently being investigated for a myriad of potential applications in the fields of medicine, electronics and other material sciences2.
Some of the most promising applications of this material include capturing individual cancer cells in the blood stream, stimulating cartilage production in damaged tissues, delivering therapeutic drugs to diseased cells, developing lithium ion battery electrodes with great storage capacity and sensors that can change color when exposed to certain chemical vapors. Earlier research has also showed that coating furniture with carbon nanofibers could serve as a flame retardant.
Nanofibers are very flexible, and can therefore be easily woven into clothing. One of the most fascinating potential applications of these nanofibers is that they could be incorporated into clothing to provide thermal insulation. Piezoelectric nanofibers can convert the energy from normal motion into an electric current that could be used to charge devices, such as smartphones and other mobile electronic devices.
Nanofibers are also being investigated for their ability to show protection against ballistic and chemical/biological warfare. Due to these properties, nanofiber technology is currently being investigated for its application in the development of lightweight protective clothing for army personnel.
Phil Gibson and Calvin Lee’s team from the U.S. Army Soldier Systems Center at Natick investigated the thermal transfer properties of high loft nanofiber battings composed of carbon fibers as well as other polymeric fibers such as polyacrylonitrile (PAN), nylon and polyurethane. The efficiency of thermal insulation is inversely related to the size of the fibers.
Whereas both the tested materials, electrospun polyacylonitrile and meltblown pitch showed great reduction in heat transfer, the meltblown pitch carbon nanofiber batting at low bulk density showed superior insulation properties, while increasing compression levels seem to decrease the efficiency of insulation3.
On the other hand, PAN nanofiber battings showed best thermal insulation at high density. Nanofiber/aerogel composites in this study were found to exhibit superior insulating properties per unit thickness, however, the increase in weight is a concern.
Taken together, the combination of different composite materials, along with the nanofibers, seem to be the best approach to develop clothing that could provide maximum insulation. By applying as little as 3 volts (V) of energy, which is the typical output of a watch battery, this group of Researchers successfully increased the temperature of a one square inch by 40 ºC.
The hydrogel particles made of polyethylene glycol incorporated in the clothing can absorb sweat thereby preventing the inner layers from becoming wet.
Along with cold weather clothing, this fiber based insulation technology could be applied to various other gear for soldiers such as hand wear, sleeping bags, tent liners as well as in other applications related to refrigerators and storage units used for various purposes like food services.
Soldiers will be able to increase or decrease the voltage to keep them warm and comfortable while also having increased mobility due to the lighter and thinner uniforms.
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- “Nanotechnology could keep soldiers warm” – Institute of Mechanical Engineers
- “Nanofibers: Uses and Applications of Nanofibers” – UnderstandingNano.com
- “Application of Nanofiber Technology to Nonwoven Thermal Insulation” P. Gibson, C. Lee. U.S. Army Solider Systems Center.