Rheology of Ziegler–Natta and metallocene high-density polyethylenes: broad molecular weight distribution effects

The linear viscoelastic properties of two series of Ziegler–Natta and metallocene HDPEs (ZN-HDPEs and m-HDPEs, respectively) of broad molecular weight distribution (MWD) have been studied. Correlations between zero-shear viscosity and molecular weight and molecular weight distribution show that the breadth of the MWD for m-HDPEs plays a role. Other interesting correlations between the crossover modulus and steady-state compliance with MWD of both these classes of polymers have also been derived. Finally, the steady-shear viscosities from capillary rheometry are compared with LVE data to check the applicability of the empirical Cox–Merz rule. It is shown that the original Cox–Merz rule is applicable for the ZN-HDPEs, while it apparently fails for the m-HDPEs. However, once the capillary data for m-HDPEs are corrected for slip effects, the applicability of the Cox–Merz rule is validated for their case as well.