The Effect of Intrinsic Viscosity on the Physical Properties of Polyethylene Terephthalate Filament Yarn

Intrinsic viscosity and molecular weight distribution are critical properties of polyethylene terephthalate (PET), significantly influencing its crystallinity, rheological behavior, and thermal characteristics. This study examines the mechanical and thermal properties of undrawn and drawn yarns produced via melt spinning using three PET chips with intrinsic viscosities of 0.63, 0.64, and 0.68 dl/g. The chips were dried and melt-spun at take-up speeds of 2000–3000 m/min. Thermomechanical properties were evaluated through tensile tests, thermal shrinkage, resilience, and dyeing tests, while microstructure was analyzed using birefringence, X-ray diffraction (XRD), and differential scanning calorimetry (DSC). Results showed that undrawn yarns produced from the higher intrinsic viscosity PET chips exhibited up to 55% higher birefringence across all take-up speeds. For drawn yarns with 40–50% elongation at break, XRD analysis revealed enhanced crystal growth and a 6% increase in crystallinity, correlating with approximately 10% improvements in initial modulus, tensile strength, and resilience. Additionally, textured yarns with higher intrinsic viscosity demonstrated a 7% reduction in crimp stability but a 10% increase in resilience. These findings highlight the significant role of intrinsic viscosity in enhancing the structural and mechanical properties of PET yarns, offering valuable insights for optimizing PET processing and performance in industrial applications.