Measurement of Stress Distribution in Barus Effect of Polymer Melts by Flow Birefringence

Abstract

Flow birefringence was applied to observation of the entrance flow and emerging flow of polymer melts through parallel plate nozzles. Isochromatic and isoclinic patterns were measured with conventional apparatus for photoelasticity. The flow field near the exit of the nozzle was divided into three parts : equilibrium flow region, rapid swelling region and slow swelling region. The stress distribution over the cross-section of the exit was different from that of the fully developed flow. The flow inside the exit began to change near a point one third of the thickness of the nozzle inside the exit. The relaxation was mostly completed near the point four times thickness of the nozzle outside the exit. The existence of exit pressure was shown. The stress, which might be strongly related to occurrence of melt fracture, was concentrated at the edge of the nozzle entrance.