What is silicone rubber?
Silicone rubber is a synthetic elastomer made from silicone, a polymer composed of silicon, oxygen, carbon, and hydrogen. As an elastomer, it has elastic properties similar to rubber. But what exactly are silicone rubber properties and uses? In this guide, we’ll explore everything you need to know about silicone rubber, including:
Advantages of silicone rubber
Silicone polymer is a high-performance elastomer characterised by several factors. For starters, it’s flexible, durable and chemically inert, so it’s not only oil resistant, but doesn’t react with most substances. With good chemical stability, it's ideal for use in applications exposed to harsh chemicals, such as industrial machinery and medical equipment. Silicone rubber is also temperature resistant, meaning it can withstand a wide temperature range: 204°C to 232°C on the high end, which makes it ideal for masking, and a low temperature limit of -53°C to -73°C.
The advantages of silicone rubber give it more uses than organic rubber. Example: with general weather resistance, it stands up to UV and extreme environments, unlike most organic rubbers.
This rubber-like material offers excellent electrical insulation properties due to its molecular structure. Its silicon-oxygen bond is highly stable and doesn’t easily break down, even when exposed to electrical fields. It’s little wonder that silicone rubber is often used as an electrical insulator in high-voltage applications. Silicone rubber electrical properties make it ideal for a range of electronic and electrical applications, such as consumer appliances and data centre cabinets.
Highly purified silicone rubber is also biocompatible, meaning it’s well tolerated by living tissue. It can also be modified with other materials to improve its biocompatibility, such as coatings that reduce the risk of infection or inflammation.
You can learn more in our guide, Material Standards for Medical Manufacturing.
Silicone rubber properties
Silicone rubber advantages and disadvantages come down to its properties. It has relatively long polymer chains and high molecular weight. Its molecular structure consists of siloxane bonds. The presence of these bonds contributes to its low thermal conductivity, making it an excellent heat resistant and thermally stable material. This makes silicone rubber incredibly versatile. However, due to the weak nature of the chains, silicone rubber can be prone to tearing under certain conditions. Nonetheless, silicone rubber is still known for its flexibility and durability, and it’s often reinforced with fumed silica to make it more tear resistant.
Material properties of silicone rubber
Silicone rubber material properties are the physical, chemical, or mechanical characteristics that define its functionality and suitability for manufacturing. In essence, the material properties play a vital role in defining its overall performance and usability. Let’s take a closer look at the properties of silicone rubber.
Silicone rubber mechanical properties
The characteristics that impact silicone rubber’s mechanical strength and capacity to be formed into desired shapes are referred to as its mechanical properties. These include the following:
| Mechanical Properties | Minimum & Maximum Values |
|---|---|
| Shore Hardness A | 4.00 – 95.0 (average value: 50.9) |
| Shore Hardness D | 14.5 – 95.2 (average value: 53.6) |
| Shore Hardness OO | 10.0 – 86.0 (average value: 52.3) |
| Tensile Strength, Ultimate | 0.138 – 165 MPa |
| Tensile Strength, Yield | 0.0448 – 145 MPa |
| Modulus of Elasticity | 0.000517 – 1.90 GPa |
| Compressive Modulus | 0.000200 – 0.00590 GPa |
| Poisson’s Ratio | 0.500 |
| Shear Modulus | 0.0000689 – 1.83 GPa |
| Shear Strength | 0.965 - 6.05 MPa |
| Tear Strength | 0.877 - 125 kN/m |
| Compression Set | 3.00 – 77.3% 3.10 – 46.0% @Temperature 70°C – 302°C 3.10 – 46.0% @Time 79200 – 259000 sec |
| Tensile Set | 5.10 – 6.00% |
Physical properties of silicone rubber
A physical property is a characteristic not associated with any change in its chemical composition. Additives can change a material’s physical properties, for example. The following are silicone rubber physical properties in its unchanged state:
Silicone rubber thermal properties
Thermal properties refer to how a material responds when heat is applied to it. This response can take many forms, such as an increase in temperature. Thermal properties of silicone rubber include the following:
| Thermal properties | Values |
|---|---|
| Glass Transition Temperature | -120°C – 118°C |
| Coefficient of linear thermal expansion (CTE, linear) | 11.0 – 335 µm/m-°C |
| CTE, linear, Transverse to Flow | 20.0 – 40.0 µm/m-°C |
| Brittleness Temperature | -73.0°C – -60.0°C |
| Specific Heat Capacity |
0.320 – 1.26 J/g-°C |
| Thermal Conductivity |
0.0600 – 6.50 W/m-K 0.150 – 3.3867 W/m-K 1.50 – 4.69 W/m-K 1.50 – 4.69 W/m-K |
How to use silicone rubber
Begin by determining the specific requirements of your application. This may involve identifying the necessary properties, size and shape of the material, and any environmental factors that could affect its performance. Once you’ve chosen your silicone rubber, you should prepare the material by cutting or shaping it to fit your specific application. Depending on your needs, you can apply the silicone rubber material using different methods such as adhesive bonding, mechanical fastening, or moulding.
You can learn more in EPDM vs. Silicone: A Simple Guide.
What is silicone rubber used for?
Silicone rubber uses are vast, thanks to its material properties. For example, it’s often used as a sealant due to its excellent adhesion, flexibility, and chemical resistance. Silicone rubber sealant uses are common – it’s also water resistant, and used in plumbing to seal joints, automotive applications to seal gaps around windscreens and doors, electronic components and enclosures to protect against moisture and dust ingress.
Sealants and high-performance adhesives are often room temperature-vulcanising silicone, called RTV silicone rubber. This means the silicone cures at room temperature.
Another common silicone rubber application can be found in masking components. Silicone rubber, as either caps and plugs or masking tape, moulds to different shapes and withstands high temperatures and chemicals.
You can learn more in How to Choose the Right High-Temperature Masking Tape.
Examples include:
You might find it helpful to read our Masking Materials Selection Guide.
Applications of silicone rubber
From silicone rubber for medical applications to automotive uses, the material is commonly used in the following ways:
| Industry | Application | Why |
|---|---|---|
| Automotive | O-rings, waterproof connectors, hoses | High-temperature resistance, oil & flex fatigue resistance |
| Consumer Electronics | Microwave oven window gaskets & drive belts, defrosters, wiring | Electrical insulation, low- and high-temperature resistance, low compression set |
| Machinery | Solar hoses, hot-stamping rollers, lost-wax casting | Chemical & high-temperature resistance, low compression set, weather resistant |
| Outdoor Enclosures | O-rings, gaskets, seals, ventilation covers, keyboards & buttons | Weather & moisture resistance, flexibility, resistance to high-temperatures |
| Medical Equipment | Balloon catheters, tubing for feeding, drainage, & use with peristaltic pumps, seals, valves, hearing aids | Biocompatibility, high-temperature & chemical resistance |
| Office Equipment | EMI gaskets, keypads (calculators & computer keyboards) | Electrical insulation, flame resistant, thermal conductivity, high-temperature & flex fatigue resistance |
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Questions?
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