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 poly propylenes is studied. The samples underwent different controlled pero xide degradation rates, so they exhibit different molecular distributi ons. The relaxation spectrum is obtained by assuming that it takes the shape of a Log-Normal distribution. It is in agreement with the linea r viscoelasticity theory by providing limiting values, contrary to oth er models. Moreover, the ratio tau omega/tau n which takes place in th is law is very useful to distinguish the synthesis differences of the samples when the Melt Flow Index alone cannot.