By Josh Perry, Editor
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According to a report from the American Chemical Society (ACS), researchers from the Ulsan Institute of Science and Technology (UNIST) in South Korea have developed a wearable heater by modifying woven Kevlar fabric with copper-nickel nanowires.

UNIST researchers created a heater from Kevlar. (UNIST)

The nanowires were grown between two Kevlar sheets and the spaces between the wires were filled with a resin that contained graphene oxide for uniform heating.

“Applying a low voltage (1.5 volts) to the composite material caused a rapid and uniform increase in surface temperature to 158°F — a typical ‘high’ setting on a heating pad,” the report explained. “In another experiment, the team showed that the material acted as a thermal insulator by reflecting infrared radiation emitted from a hot plate set at human body temperature.”

The modified Kevlar material produced breathable, flexible, and wearable heaters that retained the mechanical strength of the original. There is the potential that this could produce clothing for cold-weather environments as well as protective gear for police or military personnel.

The research was recently published in Nano Letters. The abstract stated:

“Thermotherapy is a widespread technique that provides relief for muscle spasms and joint injuries. A great deal of energy is used to heat the surrounding environment, and heat emitted by the human body is wasted on our surroundings.

“Herein, a woven Kevlar fiber (WKF)-based personal thermal management device was fabricated by directly growing vertical copper–nickel (Cu–Ni) nanowires (NWs) on the WKF surface using a hydrothermal method. The treated WKF was combined with reduced graphene oxide (rGO) dispersed in polydimethylsiloxane (PDMS) to form composites using vacuum-assisted resin transfer molding (VARTM).

“This WKF-based personal thermal management system contained a conductive network of metallic NWs and rGO that promoted effective Joule heating and reflected back the infrared (IR) radiation emitted by the human body. It thus behaved as a type of thermal insulation. The Cu–Ni NWs were synthesized with a tunable Ni layer on Cu core NWs to enhance the oxidation resistance of the Cu NWs.

“The combined effect of the NW networks and rGO enabled a surface temperature of 70 °C to be attained on application of 1.5 V to the composites. The Cu₃Ni₁–WKF/PDMS provided 43% more thermal insulation and higher IR reflectance than bare WKF/PDMS. The absorbed impact energy and tensile strength was highest for the Cu₁Ni₃- and rGO-integrated WKF/PDMS samples.

“Those Cu–Ni NWs having higher Ni contents displayed better mechanical properties and those with higher Cu contents showed higher Joule heating performance and IR reflectivity at a given rGO loading. The composite shows sufficient breathability and very high durability. The high flexibility of the composites and their ability to generate sufficient heat during various human motions ensures their suitability for wearable applications.”