CORRELATIONS BETWEEN RELAXATION-TIME SPECTRUM AND MELT-SPINNING BEHAVIOR OF POLYPROPYLENE .1. CALCULATION OF THE RELAXATION SPECTRUM AS A LOG-NORMAL DISTRIBUTION AND INFLUENCE OF THE MOLECULAR-PARAMETERS

The linear viscoelastic behavior of commercial broad-distribution polypropylenes is studied. The samples underwent different controlled peroxide degradation rates, so they exhibit different molecular distributions. The relaxation spectrum is obtained by assuming that it takes the shape of a Log-Normal distribution. It is in agreement with the linear viscoelasticity theory by providing limiting values, contrary to other models. Moreover, the ratio tau omega/tau n which takes place in this law is very useful to distinguish the synthesis differences of the samples when the Melt Flow Index alone cannot.