Flow birefringence of polymer melts: Application to the investigation of time dependent rheological properties

Abstract

Transient stresses including normal stresses, which are developed in a polymer melt by a suddenly imposed constant rate of shear, are investigated by mechanical measurement and, indirectly, with the aid of the flow birefringence technique. For the latter purpose use is made of the so-called stress-optical law, which is carefully checked. It appears that the essentially linear model of the "rubberlike liquid", as proposed by Lodge, is capable of describing the behaviour of polymer melts rather well, if the applied total shear does not exceed unity. In order to describe also steady state values of the stresses successfully, one should extend measurements to extremely low shear rates. These statements are verified with the aid of a method which was originally designed by Schwarzl and Struik for the practical calculation of interrelations between linear viscoelastic functions. In the present paper dynamic shear moduli are used as reference functions. © 1976 Dr. Dietrich Steinkopff Verlag.