New conductive cotton fibre blend for smart textiles

Researchers from Washington State University have developed a single strand of fibre that has the flexibility of cotton and the electric conductivity of a polymer called polyaniline. The material shows good potential for wearable e-textiles. The researchers tested the fibres with a system that powered an LED light and another that sensed ammonia gas, detailing their findings in the journal Carbohydrate Polymers.

WSU textile researcher Hang Liu said the researchers have one fibre in two sections: one section is the conventional cotton and strong enough for everyday use, and the other side is the conductive material. “The cotton can support the conductive material which can provide the needed function,” Liu said.

While further development is needed, the aim is to integrate fibres like these into apparel as sensor patches with flexible circuits. The patches could be part of uniforms for firefighters, soldiers or workers who handle chemicals to detect for hazardous exposures. The patches could also be suitable for health monitoring or exercise shirts that can do more than current fitness monitors.

“We have some smart wearables, like smart watches, that can track your movement and human vital signs, but we hope that in the future your everyday clothing can do these functions as well. Fashion is not just colour and style, as a lot of people think about it: fashion is science,” Liu said.

The researchers worked to overcome the challenges of mixing the conductive polymer with cotton cellulose. Polymers are substances with large molecules that have repeating patterns. The researchers used polyaniline, known as PANI, a synthetic polymer with conductive properties that is used in printed circuit board manufacturing. While intrinsically conductive, polyaniline is brittle and cannot be made into a fibre for textiles. To solve this, the researchers dissolved cotton cellulose from recycled t-shirts into a solution and the conductive polymer into another solution. These two solutions were then merged side-by-side and the material was extruded to make one fibre.

The result showed good interfacial bonding, meaning the molecules from the different materials would stay together through stretching and bending. Achieving the right mixture at the interface of cotton cellulose and polyaniline was a delicate balance, Liu said. “We wanted these two solutions to work so that when the cotton and the conductive polymer contact each other they mix to a certain degree to kind of glue together, but we didn’t want them to mix too much, otherwise the conductivity would be reduced,” Liu said.

Image caption: Hang Liu examines fibre samples developed at her lab. Image credit: Dean Hare, WSU Photo Services.