ELONGATIONAL FLOW OF POLYETHYLENES IN ISOTHERMAL MELT-SPINNING

The elongational behavior of two polyethylenes with different structur es, namely, a low-density polyethylene and a linear low-density polyet hylene, has been investigated by isothermal melt spinning. The length along the spinline has been rescaled according to time. The evolution of the calculated elongational viscosity versus time has been compared to the transient elongational viscosities measured after imposition o f a constant extension rate. The data demonstrate that these two situa tions, which are in many ways similar, give nearly the same results. C onsequently, the viscosity which can be obtained from a fiber spinning experiment is a transient elongational viscosity. Differences in the elongational behavior between the long branched and the linear polyeth ylene are presented such as displayed in the spinning experiment. The strong influence on practical parameters such as melt strength or brea king stretch ratio is demonstrated.