Extrudate swell properties of high density polyethylene melts in annular die

Abstract

This research presents a study about extrudate swell properties of high density polyethylene melts in annular die, extruded in a capillary rheometer through 3 types of annular die: normal annular die, convergent annular die and divergent annular die. Each type of die had a die gap of 1mm, 1.5 mm and 2 mm, respectively. Results of the experiment showed that extrudate swell of high density polyethylene melts occurred in both diameter swell and thickness swell ratio. The swell measured in all 3 types of die tended to be higher with the increase of shear rate and the decrease of 2 mm, 1.5 mm to 1 mm die gap by an average of 12%. This occurrence could be explained from measurement of flow properties in all 3 types of die which had increasing shear stress due to the decrease of die gap by an average of 10%. Moreover, it was also found that the thickness swell ratio was higher than the diameter swell by an average of 45% in all sizes of die gap. This could be explained from the Stress distribution which was more dense at the mandrel's surface when the die gap of annular die decreased.