Melt fracture of HDPEs: Metallocene versus Ziegler-Natta and broad MWD effects

The melt fracture of high-density polyethylenes (HDPEs) is studied primarily as a function of molecular weight and its distribution for broad molecular weight distribution metallocene and Ziegler-Natta catalyst resins. It is found that sharkskin and other melt fracture phenomena are very different for these two classes of polymers, although their rheological behaviors are nearly the same for many of these. Moreover, the metallocene HDPE shows significant slip at the die wall without exhibiting stick-slip transition. Important correlations are derived between the critical conditions for the onset of melt fracture and molecular characteristics.