Scientists have created a textile-based wearable heater based on highly durable conductive yarns.
An electrically conductive and durable yarn was sewn onto fabric and became a wearable heater (high temperatures indicated by yellows and reds) when a safe voltage was applied. Image credit: Pattanarat et al., doi: 10.1021/acsami.1c13329.
Lightweight wearable heaters with heating elements embedded within the fabric could help keep people warm, but previous attempts have resulted in hot stiff wires or threads that cannot be safely washed.
Recently, researchers have treated fabric and yarn with poly(3,4-ethylenedioxythiophene) and poly(4-styrenesulfonate). This flexible coating warmed up the materials and stayed in place after washing.
However, the polymers were not conductive enough for personal heating, and some compounds added to make them more conductive could irritate the skin.
Dr. Rawat Jaisutti from the Department of Physics at Thammasat University and colleagues from Thailand and Korea wanted to improve upon the two-polymer coating applied to yarn so that it could distribute heat at a safe operating voltage when sewn into fabric.
As a first step, they dipped the polymer-coated cotton yarn into ethylene glycol, which is not irritating to human skin.
When they applied voltage to the material, it warmed up, requiring lower voltages to reach high temperatures than some previously reported flexible heaters.
Then the researchers washed treated yarn either repeatedly with water or once with detergent.
They found that although in both instances there was a slight loss of conductivity, this loss was significantly less than a version without the ethylene glycol.
Finally, they sewed multiple pieces of the yarn into a TU pattern on a bit of fabric with an additional fabric backing.
When the heater was connected to a three-volt power supply and attached to a person’s wrist, the heat distribution in the thermal wristband was steady as it was bent back and forth.
“The heating elements made from the conductive yarns showed an excellent distribution of temperature and could be heated up to 150 degrees Celsius (302 degrees Fahrenheit) at a sufficiently low driving voltage of 5 V,” the authors explained.
“Also, the heating elements showed stable Joule heating performance under repeated bending stress and 2,000 cycles of stretching and releasing.”
“To demonstrate its practical use for on-body heating systems, a lightweight and air-breathable thermal wristband was demonstrated by sewing the conductive yarns onto a fabric with a simple circuit structure,” they said.
“From these results, we believe that our strategy to obtain highly conductive and durable yarns can be utilized in various applications, including medical heat therapy and personal heating management systems.”
The team’s work was published in the journal ACS Applied Materials & Interfaces.
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Kuntima Pattanarat et al. 2021. Wash-Durable Conductive Yarn with Ethylene Glycol-Treated PEDOT:PSS for Wearable Electric Heaters. ACS Appl. Mater. Interfaces 13 (40): 48053-48060; doi: 10.1021/acsami.1c13329
