Oscillating shear capillary rheometry (OSCAR) for polymer melts

Knowing the flow parameters of a polymer melt under steady state condition is required to assess the performance of the material in die and mold design. Often, however, this is not sufficient for a full understanding of the polymer processing behavior, and information on the linear and non-linear viscoelastic behavior is needed. In this paper, the non-linear viscoelastic behavior of a polymer under shear flow has been investigated by measuring the stress response when a cyclic oscillating shear rate in a capillary rheometer is applied. The time-dependent wall shear stress has been decomposed into in-phase viscous and elastic components. A model to interpret the experimental results is presented and applied to a well-characterized polystyrene and two polyethylenes with similar rheology but different molecular structure (HDPE and LLDPE). The relevant characteristics resulting from the model, such as the generalized elastic and viscous modulus under shear, are compared and discussed.