Hygroscopic elongation of moisture-responsive polyamide 6 fibers copolymerized with polyetherdiamine and adipic acid

Smart materials represent an emerging and highly exploited category, particularly in the creation of textiles that can sense and respond to various external stimuli, such as temperature or humidity. This study introduces for the first time the hygroscopic elongation and drying shrinkage properties of stimulus-responsive single-component polyamide (PA) fibers copolymerized with polyetherdiamine and diethylenetriamine (DETA). PA copolymers containing 5–15% polyetherdiamine were comprehensively characterized, including nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FT-IR), relative viscosity, and differential scanning calorimetry (DSC) analyses. Subsequently, these PA copolymers were successfully melt-spun into fibers and knitted into double-layered fabrics. PA fibers containing 15% polyetherdiamine showed significant results, with a moisture-absorbing elongation of 15.6% and a drying shrinkage of 94.9%. The Qmax and moisture regain of the PA fabric are 0.206 W·cm–2 and 4.4%, respectively. These moisture-driven, fiber-based smart textiles exhibit changes in breathability and shape retention at different humidity levels, thereby maintaining a more comfortable microclimate. Such textiles have great potential for widespread use in clothing, helping to improve comfort and adaptability.