Structural evolution of Poly(ethylene terephthalate) fibers in high-speed in-line drawing process

The structural evolution of poly(ethylene terephthalate) (PET) fibers under high strain rate drawing was investigated using high-speed in-line drawing process comprising three sequential zones: spinning (S), hot-drawing (D), and annealing (DA). PET fibers were drawn at take-up velocities of 5 and 6 km/min with draw ratios ranging from 1 to 2.5. Structural characterization was performed using two-dimensional wide-angle X-ray diffraction (2D WAXD), birefringence, and density measurements to investigate the evolution of the amorphous phase, oriented mesophase, and crystalline phases during the process. Fibers drawn in the D zone exhibited a highly oriented mesophase with a weak but sharp meridional (001′) peak in their 2D WAXD patterns. Structural evolution into the crystalline phase occurred independently in the DA zone, where the oriented mesophase acted as a precursor to crystallization. The mechanical properties of the fibers were predominantly influenced by the fraction and orientation of the mesophase developed in the D zone.