A team of scientists from the UK and Portugal has produced graphene-coated polypropylene (PP) fibres that can be used in wearable textiles as temperature sensors. Operating in the range of 30 to 45 ^oC at voltages as low as 1 V, textiles incorporating these fibres could be used to actively measure body temperature of the wearer.

Fibres with integrated sensing functionality overcome some key issues related to the use of monolithic sensors that are attached to either clothes or skin, such as ease of use and wearer comfort. Moreover, many attachable sensors are not robust against washing, and some require external high-power voltage supplies. The new graphene-PP based solution resolves all these issues, as described in the application-driven work published in ACS Applied Materials & Interfaces.

PP is a textile fibre material that is strong and transparent, lightweight, eco-friendly and recyclable. The researchers coat PP, an electrical insulator, with graphene to create fibres that are electrically conductive, their resistance changing with temperature. With an outlook for practical device development, the researchers tested two types of graphene that is suitable for mass production, CVD grown and shear exfoliated. The CVD grown graphene exhibited higher sensitivity to temperature, due to its better uniformity. The resistance changes by several percent across temperatures of interest, which is suitable for practical use.

Figure: Graphene on polypropylene fibre temperature sensor – real life use test. Reprinted with permission from ACS Appl. Mater. Interfaces 2020, 12, 26, 29861–29867. Copyright 2020 American Chemical Society.

In order to simulate real-life usage, the novel fibres were tested against bending for up to 1000 cycles and washing in laundry detergent at different temperatures. The devices exhibited excellent stability under all tested conditions. These sensors have potential applications in continuous measurement of human body temperature through integration in garments, or ambient temperature through integration in upholstery.