VISUALIZATION OF THE FLOW OF LOW-DENSITY POLYETHYLENE POLYSTYRENE BLENDS THROUGH A PLANAR STEP CONTRACTION

The flow of low density polyethylene (LDPE), polystyrene (PS) and a LD PE/PS 33/67 blend of the two through a planar step contraction was vis ualized. Upstream vortices were generated by the flow of the LDPE but not by the flow of PS. The flow of the LDPE/PS blend generated a conve x shaped transparent band which curved around the lip of the step cont raction and grew with increasing flow rate. This band is believed to b e due to coalescence of the dispersed phase which was observed from SE M photographs of the solidified extrudate. A small upstream vortex was observed during the flow of LDPE at the lowest flow rate. This vortex was located at the midpoint between the corner and the lip of the ste p contraction. A second vortex was observed at the lip of the die with further increase in flow rate. The two vortices merged at higher flow rates.