Abstract:

Objective Elastic electronic yarns play a significant role in the field of smart wearable electronic textiles. However, the conventional elastic conductive yarns have a strain-sensitive problem, which not only hinders the lossless transmission of signals but also limits their applications in stretchable devices. The aim of this study is to enhance the mechanical properties of these yarns by endowing them with both good elasticity and sensing performance. This research is crucial as it is essential for the development of high performance wearable electronics in meeting the growing market demand for reliable and multifunctional smart textiles.

Method The study utilized the principle of combining materials with complementary characteristics. Silver-plated nylon yarn with excellent conductivity and polyurethane resin with high elasticity were selected. The coaxial wet spinning process was employed, where the polyurethane resin solution was extruded through a concentric spinneret to encapsulate the silver-plated nylon yarn, forming a core-sheath structure. Differential stretching was then carried out by adjusting the drafting ratio between the extrusion speed and the winding speed. The prepared coaxial yarns were characterized using surface electron microscope to observe the micro-structure, tensile tester to measure the mechanical properties, and parameter analyzer to test the electrical properties.

Results SEM images revealed a distinct internal spiral structure in the prepared conductive yarns. This structure was highly correlated with the drafting ratio during the manufacturing process. As the drafting ratio increased, the number and density of the spiral structures within the yarn were notably augmented. When the drafting ratio was 1∶1, the resistance change rate of the conductive yarn reached 90%, indicating excellent conductive sensing performance. When applied for smart sports wristband, it was able to detect the slightest change in muscle tension during exercise. Slight muscle twitching, equivalent to slight stretching, triggers significant resistance changes, thus facilitating accurate monitoring of sports-related actions. When the drawing speed ratio was 1∶5, remarkable mechanical and electrical properties emerged. The resistance change rate of the conductive yarn under 300% strain is as low as 5.6%, showing outstanding stain-insensitive performance and its high elasticity. At 30% tensile strain, the change rate of resistance maintained remarkable stability in 2 000 cycles, which suggests suitability for flexible sensors in smart clothing. These sensors need to maintain a stable electrical connection during daily wear, while stretching and bending. The low resistance changes ensured reliable signal transmission, and high elongation enabled the sensor to withstand repeated mechanical stress without abrupt change, thus improving the long-term function and durability of the smart clothing.

Conclusion This study successfully developed elastic conductive yarns with tunable properties. The higher drawing ratio of 1∶5 led to a densely coiled internal structure, resulting in low resistance change under strain, high elongation at break, and excellent stability during cyclic stretching. Conversely, a 1∶1 drafting ratio provided remarkable conductive sensing performance. The strain-insensitive yarns find applications in stretchable electronics requiring stable conductivity, such as flexible sensor in smart clothing. The highly sensitive ones can be used in precise motion-sensing wearable devices. This research also shows that further optimization of spinning and drawing parameters could produce yarns with better properties. Future work might explore the integration of other functional materials into the yarn, enduring the yarn with additional characteristics such as self-repair or antibacterial capabilities. Generally speaking, this study paves the way for developing the next generation of the smart wearable electronic textiles.

Key words: internal spiral structure, strain insensitivity, wet spinning, polyurethane, conductive yarn, differential drafting, smart texiles, flexible sensor