“Miniature, wearable, electronic gadgets are ever more common in our daily lives. But currently, they are often dependent on rare, or in some cases toxic, materials. They are also leading to a gradual buildup of great mountains of electronic waste. There is a real need for organic, renewable materials for use in electronic textiles,” says Sozan Darabi, doctoral student in the department of chemistry and chemical engineering at Chalmers University of Technology and the Wallenberg Wood Science Center, and lead author of a scientific article recently published in ASC Applied Materials & Interfaces.

Together with Anja Lund, another researcher in the same group, Sozan Darabi, has been working with electrically conductive fibers for electronic textiles for several years. The focus was previously on silk, but now the discoveries have been taken further through the use of cellulose.

Built-In Electronics in Nontoxic, Renewable, and Natural Materials

The results now presented by the researchers show how cellulose thread offers huge potential as a material for electronic textiles and can be used in many different ways. Sewing the electrically conductive cellulose threads into a fabric using a standard household sewing machine, the researchers have succeeded in producing a thermoelectric textile that produces a small amount of electricity when it is heated on one side — for example, by a person’s body heat. At a temperature difference of 37 °C, the textile can generate around 0.2 μW of electricity.

“This cellulose thread could lead to garments with built-in electronic, smart functions, made from nontoxic, renewable and natural materials,” explains Darabi.

The production process for the cellulose thread has been developed by coauthors from Aalto University in Finland. In a subsequent process, the Chalmers researchers made the thread conductive through dyeing it with an electrically conductive polymeric material. The researchers’ measurements show that the dyeing process gives the cellulose thread a record-high conductivity — which can be increased even further through the addition of silver nanowires. In tests, the conductivity was maintained after several washes.

The electrically conductive yarn is produced in a “layer-on-layer” coating process with an ink based on the biocompatible polymer polyelectrolyte complex poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate), or PEDOT:PSS. The new e-textile thread measures record-high conductivity for cellulose thread in relation to volume of 36 S/cm-, which can be increased to 181 S/cm by adding silver nanowires.

The cellulose thread coated with PEDOT: PSS can handle at least five machine washes without losing its conductivity. By integrating the cellulose yarn into an electrochemical transistor, the researchers have also been able to demonstrate its electrochemical function.

The Benefits of E-Textiles and Cellulose

Electronic textiles could improve our lives in several ways. One important area is healthcare, where functions such as regulating, monitoring, and measuring various health metrics could be hugely beneficial.

In the wider textile industry, where conversion to sustainable raw materials is a vital ongoing question, natural materials and fibers have become an increasingly common choice to replace synthetics. Electrically conductive cellulose threads could have a significant role to play here too, the researchers say.

“Cellulose is a fantastic material that can be sustainably extracted and recycled, and we will see it used more and more in the future. And when products are made of uniform material, or as few materials as possible, the recycling process becomes much easier and more effective. This is another perspective from which cellulose thread is very promising for the development of e-textiles,” says Christian Müller, research leader for the study and a professor in the department of chemistry and chemical engineering at Chalmers University of Technology.

This work of the research team from Chalmers is performed within the national research center Wallenberg Wood Science Center, in cooperation with colleagues in Sweden, Finland, and South Korea.

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