Characterizing the Rheological Behavior of Liquid Silicone Rubber Using a High Pressure Capillary Rheometer

The injection molding process of liquid silicone rubber (LSR) imposes high demands on the injection molding machines and the tools due to the low viscosity of silicone rubber. There is very little data which describes the rheological behavior of LSR and its influencing factors across a range of shear rates. In this study, the rheological behaviors of different types of LSR were characterized using a high pressure capillary rheometer with an apparent shear rate that ranged from 350 to 4000 1/s. In order to identify the temperature-dependent behavior, the test temperatures were varied between 27 and 42 °C. The behavior of the material at a high pressure was evaluated by analyzing the pressure profile of each measurement. All types of LSR displays a low level of viscosity from approx. 150 to 30 Pa s. As the shear rate and temperature rise, the viscosity of LSR decreases by at least 25 %. Additionally, we discover that the viscosity of LSR-materials with the same shore hardness differ strongly depending on which producers had made the materials. It was able to be shown that LSR displays homogenous material behavior across a wide range of shear rates. The low viscosity of LSR makes it well-suited for applications with complex structures, which require long flow paths in the injection molding process. If the viscosity sinks too low, the requirements for the tool construction increase, and, consequently, also the costs.