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

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.

Bio-Based Polymers for Engineered Green Materials

“…Cellulose was also used as support for metals and other polymers such as polycaprolactone through electrospinning deposition [18,19].…”

Tunable colors and conductivity by electroless growth of Cu/Cu2O particles on sol-gel modified cellulose

“…No major differences are found, except for isolated adsorbed siloxane-clusters possibly build up during prehydrolysis of the solution. By deposition of silver, no continuous layer, but additional small isolated clusters are formed on the fiber surface [18].…”

Metallisation of Textiles and Protection of Conductive Layers: An Overview of Application Techniques

“…Even in such a traditional area such as clothing, the modern lifestyle and new technologies are changing the aim and perception of textile materials, from simple protection to wearables with new functionalities and added value. Recently, researchers have shown an increased interest in flexible, electrically conductive textiles, which, in combination with different electronic components and circuit boards on the textile surface, represent electronic textile systems (so called e-textiles), with applications in photodynamic therapy, electronic sensors, flexible batteries, heating fabrics and light emitting displays [1][2][3]. Several approaches/techniques have been proposed in the literature about how conductivity can be implemented into flexible surfaces, (i) fabrics are weaved or knitted from conductive yarns, (ii) surfaces are sewn or embroidered with conductive threads, and (iii) those specially treated to impart conductivity, i.e., by chemical coating, surface metallization (e.g., copper (Cu), silver (Ag) or nickel (Ni) nanoparticles (NPs)), deposition of conductive fillers (carbon black or carbon nanotubes) and coating of conductive polymers (e.g., polyaniline, polypyrrole or poly-3,4-ethylenedioxythiophene), achieving Some examples of these novel products are flexible heaters, panels and actuators, electrostatic discharge clothing, high-performance sportswear and embedded healthmonitoring devices (recording data related to body temperature, heartbeat, moisture, etc.…”