Extrudate swell of high density polyethylene. Part III: Extrusion blow molding die geometry effects

Two high density polyethylene resins—801 and 802— are examined with regard to their isothermal, time‐dependent, and nonisothermal swelling properties when emerging from two annular and three diverging dies. The short time swelling characteristics of samples 801 and 802 are very important for these dies, resulting in a lower diameter swell for the latter, independent of the die geometry or flow rate. Output variations have much less impact on the swelling behavior than small changes in the geometry of the die mandrel. Accordingly, shear stress and shear rate parameters alone cannot be used to explain the swelling properties of a HDPE resin in the different die geometries. Straight annular dies induce higher diameter swelling than diverging dies.