As the October chill sets in across the United States, people are pulling out their snug sweaters and electric blankets, or loading up on portable heat packets for added warmth. Sweaters and blankets, on the other hand, are cumbersome, and heat packs only operate for a short period of time. Researchers have now demonstrated a sensitive, durable fiber for lightweight wearable warmers that are recyclable and deliver continual, portable warmth in ACS Applied Materials & Interfaces.
Lightweight wearable heaters with heating elements integrated in the fabric could keep people warm, but earlier attempts have resulted in hot inflexible wires or threads that cannot be washed properly. This stretchy layer warmed up the textiles and remained in place after washing. However, the polymeric was not sufficiently conducting for personal heating, and some of the chemicals used to make them more conductive could irritate the skin. As a result, Rawat Jaisutti and colleagues sought to optimise the two-polymer coating applied to yarn so that it could transmit heat at a safe working power when sewed into cloth. The researchers began by immersing the polymer-coated cotton yarn in ethylene glycol, which is non-irritating to human skin. When scientists applied electricity to the material, it warmed up, necessitating less volts to achieve high temperatures than previously reported flexible heaters. The team then washed the treated yarn multiple times with water or once as well detergent. They discovered that, while there was a modest loss of conductivity in both cases, it was substantially less than in the ethylene glycol-free variant. Finally, the researchers wove many pieces of yarn into a “TU” design on a layer of cloth with an additional piece of fabric backing. When a three-volt power supply was linked to the heater and affixed to a person’s wrist, the heat distribution in the thermal wristband was consistent as it was twisted back and forth. The bracelet, according to the researchers, can also be powered by batteries via an open circuit for greater mobility.

The authors thank 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 for their support.