A comparative study on extrudate swell ratio of polystyrene in a capillary rheometer and a single screw extruder

This article offers a comparative discussion on the extrudate swell ratios and velocity profiles of polystyrene melt flow using the same die with two different machines which were a constant-rate capillary rheometer and a single screw extruder. The swelling ratio and melt velocity profiles were simultaneously measured at different positions across the die diameter, with and without application of a magnetic field to the die. The results suggested that the overall swell ratio of the PS melt measured in the extruder was greater than that in the rheometer, this being caused by the differences in the flow properties of the melt in these two machines. The discrepancies in the radial extrudate swell profiles from the rheometer and extruder could be explained by the velocity profile development. When an electro-magnetized die was used, the swelling ratio of the melt changed with magnetic flux density and was affected by the size of the machinery used.