R. Fulchiron et al., CORRELATIONS BETWEEN RELAXATION-TIME SPECTRUM AND MELT-SPINNING BEHAVIOR OF POLYPROPYLENE .2. MELT-SPINNING SIMULATION FROM RELAXATION-TIMESPECTRUM, Polymer engineering and science, 35(6), 1995, pp. 518-527
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.