*Article* **Piezo-Sensitive Fabrics from Carbon Black Containing Conductive Cellulose Fibres for Flexible Pressure Sensors**

**Julia Ullrich 1, Martin Eisenreich 1, Yvonne Zimmermann 1, Dominik Mayer 2, Nina Koehne 2, Jacqueline F. Tschannett 3,†, Amalid Mahmud-Ali 3,† and Thomas Bechtold 3,\*,†**


Received: 18 October 2020; Accepted: 13 November 2020; Published: 16 November 2020

**Abstract:** The design of flexible sensors which can be incorporated in textile structures is of decisive importance for the future development of wearables. In addition to their technical functionality, the materials chosen to construct the sensor should be nontoxic, a ffordable, and compatible with future recycling. Conductive fibres were produced by incorporation of carbon black into regenerated cellulose fibres. By incorporation of 23 wt.% and 27 wt.% carbon black, the surface resistance of the fibres reduced from 1.3 × 10<sup>10</sup> Ω·cm for standard viscose fibres to 2.7 × 10<sup>3</sup> and 475 Ω·cm, respectively. Fibre tenacity reduced to 30–50% of a standard viscose; however, it was su fficient to allow processing of the material in standard textile operations. A fibre blend of the conductive viscose fibres with polyester fibres was used to produce a needle-punched nonwoven material with piezo-electric properties, which was used as a pressure sensor in the very low pressure range of 400–1000 Pa. The durability of the sensor was demonstrated in repetitive load/relaxation cycles. As a regenerated cellulose fibre, the carbon-black-incorporated cellulose fibre is compatible with standard textile processing operations and, thus, will be of high interest as a functional element in future wearables.

**Keywords:** conductive fibres; cellulose fibres; pressure sensor; smart textiles; viscose fibres; carbon black
