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Durable Yarn for Lightweight Wearable Heaters to Provide Constant Warmth

During fall, people throughout the United States tend to use their electric blankets and cozy sweaters, or stock upon handheld heat packets for more warmth.

Durable Yarn for Lightweight Wearable Heaters to Provide Constant Warmth
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: Adapted from ACS Applied Materials & Interfaces 2021,

However, blankets and sweaters are heavy, and heat packs just work for some time. At present, scientists have come up with a conductive, durable yarn for lightweight wearable heaters that can be re-used and offer steady and movable warmth. The study has been reported in the journal ACS Applied Materials & Interfaces.

Lightweight wearable heaters that come with heating elements fixed inside the fabric could be of great help to people to keep them warm. However, early attempts have ended up in hot stiff wires or threads that cannot be washed safely.

In recent times, scientists have treated fabric and yarn with poly (4-styrenesulfonate) and poly (3, 4-ethylenedioxythiophene). This flexible coating heated the materials and stayed in place even after washing.

But the polymers were not highly conductive for personal heating, and a few compounds that were added to make them more conductive could cause skin irritation. Thus, Rawat Jaisutti and collaborators wanted to enhance the two-polymer coating applied to yarn so that it could spread heat at a safe operating voltage on being stitched into the fabric.

In the first stage of the process, the scientists soaked the polymer-coated cotton yarn into ethylene glycol, which does not cause any irritation to the skin. When the voltage was applied to the material, it heated up and needed lower voltages to attain high temperatures compared to a few earlier reported flexible heaters.

Furthermore, the treated yarn was repeatedly washed by the team either with water or once with detergent. They discovered that although in both cases there was a minor loss of conductivity, this loss was considerably less compared to a version without the ethylene glycol.

In the end, the scientists sewed multiple pieces of the yarn into a “TU” pattern on a bit of fabric with an extra fabric backing. Upon connecting the heater to a 3-V power supply and attaching it to a person’s wrist, the heat distribution in the thermal wristband was stable as it was bent back and forth. Also, the scientists add that the wristband can be powered by a battery through an external circuit for high portability.

The researchers acknowledge financial support from the Thammasat University Research Unit in Innovative Sensors and Nanoelectronic Devices, the Thailand Research Fund, the Thailand Office of Higher Education Commission, and the National Research Council of Thailand.

Journal Reference:

Pattanarat, K., et al. (2021) Wash-Durable Conductive Yarn with Ethylene Glycol-Treated PEDOT:PSS for Wearable Electric Heaters. ACS Applied Materials & Interfaces.

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