Rheological insights: A comparative analysis of viscosity determination techniques for liquid silicone rubber injection moulding simulation

For successful injection moulding simulations, the viscosity change under shear and various temperatures must be reliably determined in a fashion that is as close as possible to the injection moulding reality. Within this context and motivated by it, this work presents a critical comparison among state-of-the-art methodologies currently employed to determine liquid silicone rubber’s resistance to shear flow: rotation-based (oscillatory and steady modes) and pressure-driven (based on the application of a high pressure capillary rheometer, HPCR). Among these methodologies, the steady shear rotational approach and the HPCR deliver viscosity values that are in accordance with each other. This fact is justified by the sample’s state under shear: the filler structure is disturbed during both experiments, reaching a common ground for viscosity determination. On the other hand, oscillatory experiments under linear viscoelastic conditions deal with a sample with intact filler network under mechanical equilibrium, giving rise to the Cox–Merz proposition disagreement. When non-linear viscoelastic conditions are met, i.e., high strain amplitudes are applied, causing a shift out of mechanical equilibrium, all methodologies lie in the same viscosity trend within a shear range. This correlation can serve as a shortcut for viscosity determination applied to material data characterization, leading to faster experiments and more accurate polymer processing simulations. • A comparison of rotational and pressure methods for determining LSR viscosity is presented. • Steady shear and pressure-driven methods provide consistent viscosity; oscillatory ones differ under linear conditions. • It is demonstrated the inapplicability of the Cox–Merz rule to LSR due to filler structure influence. • A shortcut for accurate viscosity determination in injection moulding simulations is presented.