Silicone rubber is a highly versatile material used in the manufacture of a wide range of industrial, commercial, and consumer products. In this blog, we provide an overview of the material, including what it is, the types available, typical applications, and the difference between liquid and solid silicone rubber.
What Is Silicone Rubber?
Silicone rubber is a high-performance synthetic elastomer composed of silicone and other molecules (e.g., carbon, hydrogen, and oxygen). It is characterized by high viscosity and elasticity, as well as better abrasion resistance, chemical stability, insulating properties, heat and cold temperature resistance, and weatherability than organic rubber.
The exact properties of a given piece of silicone rubber depend on the material’s chemical composition and structure. However, some of the generally applicable characteristics are as follows:
- Operating temperature range: -100° C to 350° C (depending on the length of exposure) and in some cases can be formulated for higher temperature ranges.
- Weatherability: resistant to wind, rain, UV radiation, and ozone
- Moisture resistance: for extended periods with 1% water absorption (for cold, warm, and boiling water)
- Steam resistance: indefinitely (for unpressurized steam)
- Chemical resistance: oils, solvents, polar organic compounds, and diluted acidic or alkaline substances
- Electrical insulation: 1TΩ·m–100TΩ·m over a wide temperature range and frequency spectrum
- Thermal conductivity: 0.2 W/mΩ·K
- Compression set: consistent from -60° C to 250° C
- Tear strength: 9.8 kN/m
Types of Silicone Rubber
As indicated above, different silicone rubber formulations result in different material behaviors. These variations can be categorized in several ways, including by molecular structure and form.
The former categorization method classifies silicone rubber by the organic group employed in its synthesis. The main types are:
- Methyl Group: dimethyl silicone rubbers (also referred to as methyl silicone or MQ silicone rubbers)
- Methyl and Phenyl Group: methyl phenyl silicone rubbers (also referred to as phenylsilicone or PMQ silicone rubbers)
- Methyl and Vinyl Group: methyl vinyl silicone rubbers (also referred to as VMQ silicone rubbers)
- Methyl, Phenyl, and Vinyl Group: PVMQ silicone rubber
- Fluoro, Vinyl, and Methyl Group: fluorinated rubber (also referred to as fluorosilicone or FVMQ silicone rubber)
The latter categorization method classifies silicone rubber by viscosity and processing method. The main types are:
- Solid Silicone Rubber: Solid silicone rubber—also sometimes called high-temperature vulcanized (HTV) rubber—has long chains of polymers with high molecular weight. It can be processed by conventional rubber processing methods.
- Liquid Silicone Rubber (LSR): LSR has shorter chains of polymers with lower molecular weight. It must be processed by specialized injection molding and extrusion methods.