General Properties & Applications of Silicone Rubber
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.
- Room Temperature Vulcanized (RTV) Rubber: RTV rubber is a one- or two-component system that falls between very soft to medium on the material hardness scale. It is typically used for sealing, encapsulation, or potting applications.
Applications of Silicone Rubber
Due to its numerous advantageous properties, silicone rubber finds application in a wide range of industries, including, but not limited to, the following:
- Aerospace (e.g., space suit elements)
- Automotive (e.g., gaskets and seals)
- Construction (e.g., coatings and sealants)
- Electrical and electronics (e.g., adhesives and encapsulants)
- Food processing (e.g., food molds)
- Medical (e.g., medical instruments components such as seals, tubes, and valves)
- Recreation (e.g., goggles and mouthpieces)
Liquid Silicone Rubber vs. Solid Silicone Rubber
As mentioned above, silicone rubber is available in several variations, including in liquid and solid forms. Below we outline the main differences between the two materials:
- Liquid silicone rubber exhibits high fluidity. The parts and products manufactured from it are generally transparent, odorless, and safe for use in applications involving direct contact with food or the skin. However, they typically require the use of expensive specialized processing equipment.
- Solid silicone rubber exhibits low fluidity. It is cheaper to purchase and process than liquid silicone rubber as it can be used alongside conventional equipment.
Silicone Rubber Capabilities at ETI
At Elastomer Technologies, we have provided exceptional elastomer processing services for over 30 years. Our team has the knowledge and skills to fulfill virtually any rubber molding or die cutting request.
For additional information about the materials and methods used in custom part fabrication, check out our blog.