Application of the ramp test from a closed cavity rheometer to obtain the steady-state shear viscosity η(γ̇)

Abstract

The steady-state shear viscosity η(γ̇)\eta (\dot{\gamma }) is required in controlling processing parameters for the extrusion processing of polymer melts. A new method, the so-called ramp test, is investigated in this study to obtain the steady-state shear viscosity with a closed cavity rheometer (CCR). To verify the method and the accuracy of the CCR data, three commercial polyolefin polymers, a low-density polyethylene (LDPE), a linear low-density polyethylene (LLDPE), and a polybutadiene (PBD), were used as model systems. Measurements of the magnitude of the complex viscosity ∣η⁎(ω)∣| {\eta }^{\ast }(\omega )| were compared with the steady-state shear viscosity data obtained by capillary rheometer and CCR. Further, time–temperature superposition master curves of the magnitude of the complex viscosity and steady-state shear viscosity obtained by CCR were developed for LLDPE and PBD. The influence of the cavity sealing on the instrument’s accuracy to obtain the steady-state shear viscosity was investigated using the finite element method simulations. Thus, it was shown that the ramp test performed by CCR is a practical method to determine reliable and reproducible data of the steady-state shear viscosity within a wide range of temperatures (T = 50–180°C) for low and high viscous materials (∣η⁎(ω)∣| {\eta }^{\ast }(\omega )| = 1.6–480 kPa s, M w = 144–375 kg mol−1).

Keywords

• steady-state shear viscosity
• closed cavity rheometer
• ramp test
• time–temperature superposition
• numerical simulation