Regulating the Microstructure of As‐Spun Polybutylene Terephthalate Fibers to Achieve High Ultimate Tensile Strength

To develop high‐strength polybutylene terephthalate (PBT) fibers, the crystalline and orientation structures of as‐spun fibers were regulated via spinning process optimization to increase hot draw ratio, employing a two‐step melt spinning and hot drawing process. As‐spun PBT fibers (intrinsic viscosity 1.26 dL/g) with varied microstructures were prepared by controlling take‐up speed (500–3000 m/min) and spinneret draw ratio. Crystalline morphology, crystallinity, and degree of orientation were characterized by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and Fourier transform infrared spectroscopy (FTIR). The as‐spun fibers exhibited crystallinity above 30%, but the relatively stable α‐form crystals formed during the cooling‐drawing process hindered further drawing deformation. By optimizing extrusion and take‐up speeds, a combination of low take‐up speed and moderate spinneret draw ratio promoted the formation of as‐spun fibers with low orientation and small crystalline domains, yielding excellent post‐drawability. After hot drawing, the resulting PBT fibers achieved tensile strength up to 6.8 cN/dtex, high crystallinity, and highly oriented β‐form crystals. This work provides technical support for the industrial production of high‐strength PBT fibers.