CORRELATIONS BETWEEN RELAXATION-TIME SPECTRUM AND MELT-SPINNING BEHAVIOR OF POLYPROPYLENE .2. MELT-SPINNING SIMULATION FROM RELAXATION-TIMESPECTRUM

Using an integral nonlinear constitutive equation including the Log-No rmal relaxation spectrum, the fiber-spinning behavior of commercial po lypropylenes is studied. The relaxation spectrum is strongly related t o the molecular weight distribution. Moreover, by means of a finite el ement analysis, simulated stress and velocity profiles are obtained ei ther in isothermal or nonisothermal cases. In the isothermal case, bro adening the relaxation spectrum leads to more pronounced curvature of the velocity profile. In the nonisothermal case, the critical draw rat io is sensitive to the mean relaxation time which depends on both aver age molecular weight and distribution breadth. It is shown that increa sing the average relaxation time leads to a less rapid growth of the v elocity. Furthermore, this effect is less pronounced when the relaxati on spectrum is wider.