Flexible, High Sensitivity, and Wide-Range Stability Humidity-Sensing Fiber with Low Temperature and Pressure Interference

This study presents an innovative poly(vinyl alcohol)/potassium hydroxide-thermoplastic polyurethane (PKT) skin-core composite fiber for high-performance flexible humidity sensing, fabricated via a two-step process combining wet spinning and solution impregnation. The unique gradient deposition of the poly(vinyl alcohol)/potassium hydroxide (PVA/KOH) functional layer creates a hierarchical 3D porous structure, while the moisture-triggered dissolution of potassium hydroxide (KOH) into a liquid electrolyte enables dynamic conductivity modulation. The PKT fiber demonstrates breakthrough performance: (1) ultrahigh sensitivity (a relative current change of over 2800%), surpassing conventional carbon- and metal oxide-based sensors; (2) wide-range stability (15–90% relative humidity (RH)); and (3) low interference capability under varying temperature and pressure conditions. The fiber’s rapid response/recovery (11.4 s/6.4 s in a wide humidity response range of 18%–80% RH) and minimal hysteresis stem from its porous architecture and reversible water adsorption–desorption mechanism. Practical applications in wearable healthcare are highlighted, including noncontact respiratory monitoring and distinct identification of oral/nasal breathing patterns. The mild processing conditions (≤90 °C) and textile-compatible technique address scalability challenges, positioning PKT fibers as a promising platform for next-generation humidity sensors.