Abstract:

Objective In order to solve problems of existing fabric-based flexible sensors, such as single functionality, complex structure, dependence on external electrodes, and insufficient comfort, this study combines conjugate electrospinning and in-situ polymerization to construct a polyurethane/carbon nanotubes/polypyrrole (PU/CNTs/PPy) composite silver-coated core-spun yarn with core layer electrodes of silver-coated polyamide yarns and the ability to sense pressure, temperature and humidity. The aim is to simplify the sensor structure, enhance its flexibility, wearability and integration, and provide a yarn-level sensing unit basis for the construction of multi-functional smart textiles.

Method The PU/CNTs silver-coated core-spun yarn was prepared by directly coating the surface of silver-coated polyamide yarns with PU/CNTs composite nanofibers using conjugate electrospinning technology. Subsequently, PPy nanoparticles were grown on the surface of PU/CNTs fibers through in-situ polymerization to form the PU/CNTs/PPy composite silver-coated core-spun yarn. The morphology, chemical structure and tensile properties of the yarn were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and mechanical tests, and its resistance response characteristics and wearable application performance to pressure, temperature and humidity stimuli were systematically tested.

Results The results showed that the nanofibers in the PU/CNTs silver-coated core-spun yarn prepared by conjugate electrospinning were orderly arranged along the yarn axis. After in-situ polymerization, PPy nanoparticles were uniformly distributed on the fiber surface and in the fiber gaps, forming a continuous conductive network. Infrared spectra analysis suggested that PU, CNTs and PPy formed a stable composite structure through hydrogen bonds and π-π interactions. The mechanical property test results demonstrated that the tensile strength and elongation at break of the PU/CNTs/PPy composite silver-coated core-spun yarn reached 7.9 MPa and 412%, respectively, which were both improved compared to the PU/CNTs core-spun yarn. After PPy modification, PPy nanoparticles were successfully and uniformly coated on the fiber surface, forming a multi-level conductive network. In pressure sensing, the resistance change rate showed a nonlinear increase with pressure, with a pressure sensitivity of 0.2 kPa^-1 in the low-pressure zone (0-100 kPa), and then gradually decreased in the medium and high-pressure zones, showing a zonal response characteristic. In temperature sensing, the resistance change rate of the PU/CNTs/PPy composite silver-coated core-spun yarn increased with temperature in the range of 20-70 ℃, with a temperature response sensitivity of 0.51%/℃, and remained stable in multiple temperature cycling tests. In humidity sensing, the yarn revealed a clear two-stage response behavior in the range of 20%-80% relative humidity, with a sensitivity of 0.15 in the low-humidity zone (20%-50% relative humidity) and increasing to 0.52 in the high-humidity zone (50%-80% relative humidity), while also demonstrating fast response and recovery characteristics. Based on the above performance, it is believed that the PU/CNTs/PPy composite silver-coated core-spun yarn can identify finger pressing, joint bending and swallowing behaviors in wearable tests, and can be utilized to detect temperature changes and respiratory humidity signals.

Conclusion This study combines conjugate electrospinning and in-situ polymerization to achieve the integration of electrodes and multi-functional sensing units within a single yarn scale, and prepares a PU/CNTs/PPy composite silver-coated core-spun yarn with core layer electrodes of silver-coated yarns. The research results show that the yarn can produce stable and distinguishable electrical responses to pressure, temperature and humidity stimuli while maintaining good mechanical properties. Its sensing ability comes from the synergy of the contact resistance network constructed by CNTs and the response of PPy to thermal and humid environments. This research provides experimental evidence for the structural design and performance regulation of multifunctional yarn-type sensors, and lays a foundation for their further application in wearable monitoring and smart textiles.

Key words: conjugate spinning, silver-coated polyamide core-spun yarn, multi-functional sensor, smart textiles, polyurethane, carbon nanotube, composite nanofiber, health monitoring