Gel point investigation of liquid silicone rubber using rheological approaches

Liquid silicone rubber (LSR) is becoming increasingly popular due to its chemical, UV, and heat resistance as well as its excellent optical properties. However, there is currently a lack of research and understanding of the rheological properties of the material. During the processing of liquid silicone rubber, the material can assume different rheological states. In the present work, both the physical and the chemical gel behavior are investigated rheologically. For this purpose, measurements are carried out with a rotational rheometer and a high-pressure capillary rheometer. Depending on the temperature and pre-shear rate, times are given for the physical gel point, after which a significantly destroyed physical network is recovered. Investigations at higher temperatures, which lead to chemical crosslinking and, therefore, to a chemical gel point, resulted in a representation of the temperature-dependent chemical gel point. The presented results serve as a material database for reliable simulations. [Display omitted] •Uncured Liquid Silicone Rubber (LSR) has both a physical and a chemical gel point.•In the unstressed state, uncrosslinked LSR can also be present as a physical gel at room temperature.•The physical gel of hydrogen bonds, entanglements, Van-der-Waals forces and filler-matrix interaction can be destroyed by pre-shearing.•Depending on temperature and pre-shear rate, the reversible network rebuilds to a physical gel in a very short time.•A chemical gel replaces the physical gel at higher temperatures and is irreversible due to the formation of covalent bonds.