As the fall cold sets in in the United States, people are pulling out their comfy sweaters and heated blankets, or stocking up on portable heat packs for extra warmth. But the sweaters and blankets are bulky, and the warm compresses only work for a little while. Now, researchers reporting in Applied materials and interfaces ACS demonstrate a common thread and durability for lightweight portable heaters that are reusable and provide consistent, portable heat.
Lightweight portable heaters with heaters built into the fabric could help keep people warm, but previous attempts have resulted in stiff, hot threads or threads that cannot be safely washed. Recently, researchers have treated fabrics and threads with poly (3,4-ethylenedioxythiophene) and poly (4-styrenesulfonate). This flexible coating warmed 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. Thus, Rawat Jaisutti and his colleagues wanted to improve the dual polymer coating applied to the thread so that it could distribute heat at a safe operating tension when sewn into the fabric.
First, the researchers dipped the polymer-coated cotton yarn in ethylene glycol, which is not irritating to human skin. When they applied voltage to the material, it heated up, requiring lower voltages to reach high temperatures than some previously reported flexible heaters. Then the team washed the treated yarn either repeatedly with water or once with detergent. They found that although in both cases there was a slight loss in conductivity, this loss was significantly less than a version without ethylene glycol. Finally, the researchers sewed several pieces of thread in a “TU” pattern onto a piece of fabric with additional fabric backing. When the heater was connected to a three-volt power supply and strapped to a person’s wrist, the heat distribution in the thermal bracelet was stable as it was bent back and forth. The researchers say the bracelet can also be powered by a battery via an external circuit for more portability.
The authors acknowledge funding from the Thammasat University Research Unit on Innovative Sensors and Nanoelectronic Devices, the Thai Research Fund, the Thai Office of the Higher Education Commission and the National Research Council of Thailand.
American Chemical Society
Pattanarat, K., et al. (2021) Wash-resistant conductive wire with PEDOT: PSS treated with ethylene glycol for portable electric heaters. Applied materials and interfaces ACS. doi.org/10.1021/acsami.1c13329.