Flexible Textile Strain Sensor Based on Copper-Coated Lyocell Type Cellulose Fabric.

Waleri Root,Thomas Bechtold,Barnaby Caven,Tom Wright,Tung Pham

doi:10.3390/polym11050784

Abstract

Integration of sensors in textile garments requires the development of flexible conductive structures. In this work, cellulose-based woven lyocell fabrics were coated with copper during an electroless step, produced at 0.0284 M copper sulfate pentahydrate, 0.079 M potassium hydrogen L-tartrate, and 0.94 M formaldehyde concentrations. High concentrations led to high homogeneous copper reaction rates and the heterogeneous copper deposition process was diffusion controlled. Thus, the rate of copper deposition did not increase on the cellulose surface. Conductivity of copper coatings was investigated by the resistance with a four probe technique during fabric deformation. In cyclic tensile tests, the resistance of coated fabric (19 × 1.5 cm2) decreased from 13.2–3.7 Ω at 2.2% elongation. In flex tests, the resistance increased from 5.2–6.6 Ω after 5000 bending cycles. After repeated wetting and drying cycles, the resistance increased by 2.6 × 105. The resistance raised from 11–23 Ω/square with increasing relative humidity from 20–80%, which is likely due to hygroscopic expansion of fibers. This work improves the understanding of conductive copper coating on textiles and shows their applicability in flexible strain sensors.

Highlights

Flexible conductive materials have been extensively investigated according to their promising potential applications in energy storage devices, photodetectors, pressure sensors, and light emitting displays [1,2,3]
The resistance raised from 11–23 Ω/square with increasing relative humidity from 20–80%, which is likely due to hygroscopic expansion of fibers
Several approaches are reported in the literature about how conductive substrates are implemented in large area fabrics

Summary

Introduction

Flexible conductive materials have been extensively investigated according to their promising potential applications in energy storage devices, photodetectors, pressure sensors, and light emitting displays [1,2,3]. The current research shows the feasibility of fiber/fabric coating to induce electrical conductivity. Coating of metallic copper layers on woven cellulose lyocell (CLY) fabrics through electroless deposition is important to achieve a large area sensor network for wearable smart textiles. Cellulose is an important textile substrate due to its biodegradable, biocompatible, eco-friendly, non-toxic, and renewable properties [4]. Several approaches are reported in the literature about how conductive substrates are implemented in large area fabrics. Flexible large area sensors are used for pressure and temperature sensing consisting of an organic coating on plastic and rubber substrates [6,7]. Matsuhisa et al printed elastic textile conductors of 30 × 20 cm size with silver nanoparticles which showed high conductivity after treatment [11]

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