Determination of the pressure dependence of polymer melt viscosity using a combination of oscillatory and capillary rheometer

For an accurate simulation of a high-pressure injection molding process by using the CAE software, it is important to understand the pressure sensitivity of a polymer's melt viscosity. The current work describes a method for the determination of the pressure dependence parameter D₃ of the Cross-WLF model. It uses a combined rheological technique using both dynamic and capillary rheometers. Three grades of polycarbonate homopolymers were studied in this work and their complex viscosities were measured using a dynamic shear rheometer. The dynamic data were used to obtain six out of the seven parameters of the Cross-WLF, except D₃. A capillary rheometer fitted with a counter pressure chamber was further used to characterize the pressure dependence of the zero shear viscosity and to determine the D₃ parameter. Finally, the derived parameters were validated by carrying out injection molding with a box tool and comparing the actual pressure profiles with simulation results using the Autodesk® MoldFlow® software. The validation results indicated that actual pressure profiles from the simulation were found to be less than 10% than that of injection molding. POLYM. ENG. SCI., 60:517–523, 2020. © 2019 Society of Plastics Engineers