Correlations between high-density polyethylene viscoelasticity and annular extrudate swell

Extradate swell is a key performance contributor in extrusion blow molding. The relation between extrudate swell and rheometric material characteristics is non-trivial. It is studied here for a large set of high-density polyethylenes. Extrudate swell data are derived from photographic analysis on a lab-scale annular extrusion set-up, while rheometric parameters are obtained from dynamic spectroscopy, uniaxial elongation, creep and creep recovery experimentation. The annular set-up produces thickness and diameter swell data, which are found to depend in different ways on the material viscoelasticity. The former correlates well with recoverable or storage compliance, while the latter correlates well with the ratio of storage to loss modulus.