Determination of pressure coefficient of polymer melts from shear flow

A modified capillary rheometer was used to measure strain rate-temperature-pressure dependencies of shear viscosity for injection molding grades of polymers. The modification consisted in the addition of a second chamber and a restricting needle valve below the main die, and its purpose was to determine the effect of pressure on the shear viscosity of different polymer melts. The modified White-Metzner model was employed to simultaneously fit the measured viscosity data and determine the pressure and temperature coefficients, ß and α. It has been found that not only the temperature but also the pressure factor significantly influences viscosity, and both of them are useful for the description of a polymer behaviour