Stable Helical Crimp Formation in PET / PA6 Bicomponent Filaments via Hygrothermally Enhanced Shrinkage Mismatch

Crimped filaments are important for thermal insulation, flexible actuation, and smart textiles; whereas mechanically textured monocomponent fibers often exhibit limited structural stability and durability. Herein, PET/PA6 side‐by‐side bicomponent filaments with stable helical crimp were fabricated by exploiting the physicochemical asymmetry between the two polymer phases. The helical morphology was primarily induced by shrinkage mismatch between PET and PA6 under interfacial constraint. By tailoring heat‐treatment conditions and media, the shrinkage mismatch and crimp structure were effectively regulated. Compared with dry‐heat treatment, moisture‐heat treatment enabled rapid hygroscopic plasticization of the PA6 phase, producing more uniform and stable helical crimps. Under optimized conditions of 100°C for 5 min, the filaments showed a crimp elongation of 338.46% and a crimp recovery of 78.19%. After 10 cycles of constant‐elongation stretching, the tensile strength increased by 12.28%, indicating good mechanical stability during cyclic deformation. Moreover, PET/PA6 helical yarns exhibited dual humidity–temperature responsiveness, achieving 12.5% deformation within 30 s at 80% relative humidity and 62.5% deformation within 2 s under dry heat at 85°C. These findings provide an effective strategy for developing stable smart helical fibers and responsive textile systems.