Silicone rubber and rubber play an important role in products such as shock absorbers, hoses, and seals. However, silicone rubber and rubber are completely different polymers.
What Is Rubber?
Rubber traditionally refers to natural rubber, but over time, it has come to include synthetic varieties. Natural rubber mainly comes from the rubber tree (Hevea brasiliensis), and its latex is made into natural rubber after coagulation and drying. Plants such as rubber grass and silver guayule also have the potential to extract natural rubber and can be used as alternative sources in some cases.
The main component of natural rubber is cis-polyisoprene (molecular formula (C5H8)n), with a content of more than 90%, and also contains a small amount of protein, fatty acids, sugars and ash.
In the 19th century, industrial research and application of natural rubber began to accelerate. Especially with the rise of the second industrial revolution, the demand for natural rubber increased sharply. Rubber can be used to make waterproof cloth, raincoats, footwear and daily necessities and used in automobile tires, industrial pipes and other mechanical parts.
Rubber is the main material for transportation tools such as automobiles and aircraft tires. At the beginning of the 20th century, World War 1 broke out. With the expansion of military operations during the war and the rise of mechanized warfare, the demand for rubber rose sharply. Scientists began to try to synthesize rubber substitutes from chemical raw materials to cope with the urgent need for rubber supply during the war. This was the beginning of synthetic rubber.
Synthetic rubber is made from petroleum, natural gas, etc. through polymerization. The composition of synthetic rubber is diverse. Common ones include styrene-butadiene rubber, nitrile rubber, butyl rubber, chloroprene rubber, etc., and their chemical composition and structure are different.
Therefore, the rubber we usually refer to includes both natural rubber and synthetic rubber. It can be said that rubber is a general term for a class of polymers with properties similar to those of natural rubber.
What Is Silicone Rubber?
Silicone Rubber is a synthetic polymer material made from organosilicon compounds. Its structure is typically composed of silicon (Si) and oxygen (O) atoms alternating in a silicon-oxygen chain, forming a siloxane backbone. This structure imparts the material with excellent high-temperature resistance, chemical stability, and good elasticity, among other properties. Its side groups (e.g., methyl groups — Si–CH₃) may attach to the silicon atoms, and these side groups influence the material’s elasticity, aging resistance, and other physical properties.
The history of silicone rubber dates back to the 1940s. In 1944, General Electric (GE) in the United States developed high-temperature vulcanized methyl silicone rubber, laying the foundation for its commercialization. Subsequently, the synthesis process for silicone rubber was further refined and quickly entered industrial applications.
The main component of silicone rubber is the organosilicon compound polysiloxane.
The synthesis of silicone rubber typically involves polymerization reactions of siloxanes, which are often catalyzed and then crosslinked through a vulcanization process to form an elastic material. Due to the strong Si–O bonds in its chemical structure, silicone rubber exhibits high chemical stability and excellent heat resistance.
Silicone rubber can also contain other organosilicon compounds, such as silanes, silicone resins, and organosilicone elastomers. In practical production, various organosilicon compounds, fillers, crosslinking agents, and other special additives can be used to modify its properties, meeting the needs of different applications.
Formulation of Silicone Rubber
- Fillers: Reinforcing fillers like fumed silica are added to enhance the mechanical strength of the silicone rubber.
- Pigments: For coloring the rubber.
- Stabilizers: For improving heat, UV, or chemical resistance.
The resulting compound is shaped into the desired form (e.g., by molding, extrusion) and then cured to produce the final silicone rubber product.
Rubber vs Silicone Rubber
High temperature resistance
Natural rubber works well between -40°C and 85°C. Some types of synthetic rubber, such as EPDM and Viton, can withstand temperatures up to 150°C, but most will degrade or harden at higher temperatures. It tends to become brittle at low temperatures and sticky at high temperatures.
Silicone rubber has very strong high temperature resistance, the ignition temperature of silicone rubber is also much higher than that of rubber. It can perform well at temperatures from -60°C to 230°C or even higher, and can still maintain good performance at extremely high or low temperatures. In normal temperature environments, natural rubber has stronger flexibility.
Therefore, silicone rubber is more suitable for use in industrial environments, such as the automotive industry, some shock absorbers or seals that need to withstand a wide temperature range.
Mechanical properties
Rubber has excellent tensile strength, elasticity and wear resistance.
Although silicone rubber is flexible, it is generally less durable in mechanical wear and abrasion and is more likely to tear under high mechanical stress.
Therefore, rubber is often suitable for applications that require high durability under pressure, especially at room temperature, which has a strong advantage over silicone, such as tires and heavy gaskets.
UV resistance
Silicone has stronger UV resistance than rubber.
Rubber is easily degraded by UV radiation, ozone and oxidation, especially natural rubber and some synthetic rubbers such as SBR. Additives or treatments are needed to improve resistance. For example, EPDM is designed to resist weathering and ozone exposure.
Silicone rubber has excellent UV resistance and is ideal for outdoor applications or exposure to the elements
Chemical resistance
Silicone has stronger chemical resistance than rubber.
Rubber is easily degraded when exposed to oil, fuel, and chemicals. Silicone rubber has excellent chemical resistance and is not easily degraded when exposed to oil, solvents or harsh environmental conditions.
Waterproofness
Both silicone and rubber have very excellent water resistance. Rubber should avoid exposure to high temperatures, ultraviolet rays, oil, fuel and other conditions, otherwise it will easily lose flexibility and crack.
Lifespan
Silicone has a longer service life than rubber, even when used in the most suitable temperature and environment for each.
Natural rubber can usually be used for 5-10 years in an ideal environment. There are many types of synthetic rubber, and different types have certain differences, and the general lifespan ranges from 5-15 years. Some special synthetic rubbers, such as fluororubber, can be up to 10-20 years.
In extreme outdoor environments, this exposure of rubber will shorten its life to 2-3 years. Rubber will wear faster under repeated mechanical stress. In industrial applications, frequent stress will also shorten its life.
The main factors affecting their lifespan are their own temperature stability, chemical resistance and resistance to environmental factors such as ultraviolet rays and ozone. Therefore, the service life of silicone is 20-50 years or even longer. Although silicone rubber is not as strong as some synthetic rubbers in terms of tensile strength, it is more flexible and durable in the long run.
Cost
Silicone is more expensive than both natural and synthetic rubber. Silicone is derived from silicon dioxide, the production process is complicated, resulting in high production costs. Silicone rubber provides excellent performance and service life in special or harsh environments, and has higher economic benefits in the long run. The initial cost of rubber is lower, and it is more cost-effective for general applications in mass production.
