RHEOOPTICAL INVESTIGATION OF A POLYSTYRENE MELT

The transient birefringence and the transient tensile stress of a poly styrene melt at 140 degrees C elongated with constant stretch rate (la mbda) and constant Hencky strain rate (epsilon) are presented. Compare d with the response during linear viscoelastic deformation, the values of the reduced birefringence and the reduced stress are higher when t he elongation is performed with epsilon = const., and are lower when t he elongation is carried out with lambda = const.. The stress-optical coefficient turns out to be a function of duration and rate of deforma tion.