On‐line measurement of orientation development in the high‐speed melt spinning process

On‐line measurement of birefringence was performed in the high‐speed melt spinning process of poly(ethylene terephthalate) using an apparatus that incorporates a rotating polarizer for the measurement of the optical retardation of running filament. Particular attention was paid to the detailed measurements in the vicinity of neck‐like deformation. Through the measurement at the take‐up velocity of 5 km/min, development of birefringence under the strain rate up to about 1 ms−1 was investigated. To analyze the relation between applied stress and birefringence, tension and temperature profiles of the spin‐line were calculated based on the experimentally obtained diameter profiles. Even though the strain rate is extremely high, a linear relationship between birefringence and a parameter calculated by dividing stress by temperature was confirmed to hold up to birefringence and stress/temperature values of about 0.017 and 10 kPa/K, respectively.