The high-speed spinning of poly (ethylene terephthalate) has been carried out for take-up velocity up to 10000m/min in order to investigate necking behavior. Fiber diameter and temperature were measured along the spinline by optical methods, and spinning stress was measured after the end of thinning process. Strain rate, spinning stress and elongational viscosity were estimated from the measured data.
The reduction of elongational viscosity is observed at a point where the fiber diameter is rapidly reduced, though the fiber temperature is decreased monotonously. This reduction of viscosity assigned to the onset of necking. In the case of take-up velocity of 10000 m/min, the necking begins at the fiber velocity of 288m/min at 221°C. This suggests that the necking occurs in the molten state for the ultra-high speed spinning. The necking begins at lower fiber velocity, lower stress, lower elongational viscosity and higher fiber temperature with increasing take-up velocity. This indicates that the necking is determined by the different kinds of forces along the spinline, such as spinning stress and cohesive force.