A study of coextrusion in a circular die

Abstract

Abstract An experimental study has been carried out of concentric and eccentric two‐phase flow of polymer melts in a circular die. For the study, a special die was constructed such that two separate streams of molten polymer could be supplied to the die inlet. Materials used for study were low‐density polyethylene, high‐density polyethylene, and polystyrene. In the experiment, two different capillary length‐to‐diameter ( L / D ) ratios were employed: 4 and 18. For a die having an L / D ratio of 18, wall normal stresses were measured, permitting the determination of the pressure gradient and hence the viscous property. For each set of extrusion conditions ( L / D ratio, flow rate, component ratio), extrudate samples were collected. These were later carefully cross sectioned and photographed in order to examine the shape of the interface between the two components. It has been found that the lower‐viscosity components tends to wrap around the higher‐viscosity component, which is consistent with the previous observations reported in the literature.