Properties of Liquid Silicone Rubber (Part III)

Liquid Silicone Rubber exhibits many useful characteristics. They are resistant to the environment are permeable to gas and vapor and can be colored as needed.

Main Properties of Silicone Rubber

Silicone Rubber Compounds have characteristics of inorganic and organic materials, and they offer a number of advantages in comparison to other rubbers.

Here, some of the most important properties of silicone are presented and explained.


Silicone rubbers have exceptional weatherability. The ozone normally attacks most organic rubbers and they deteriorate rapidly, but in silicone rubber, it has no effect, and the corona discharge (the process to change the superficial tension of materials) can be used without side effects. Additionally, silicone rubber can be exposed to wind, rain, and UV rays for long periods of time without changes in its physical properties. For example, the environmental stress cracking is appreciable over 10 years of exposure in zones where UV radiation is high. The elongation after sunlight exposure over 10 years decreases to 75%.

Gas Permeability

Silicone rubber thin films have better gas (H2, O2, N2, CO2) and vapor permeability than organic rubber or plastic films. Currently, one application is being investigated to use silicone rubbers as a gas and water separation membrane in oxygen enrichment systems.

Coloring Properties

In contrast to organic rubbers, the carbon black is not mandatory in the formulation of silicone rubbers to improve mechanical and physical properties of the final product.

For this reason, it is possible to have highly transparent products because of the presence of fine silica in the formulation, which works as a clarifier; that means it does not spoil the natural transparency of the silicone. Furthermore, silicone rubber is easy to color through pigments or master-batches and, in consequence, colorful molded items can be produced.

Radiation Resistance

One of the disadvantages of silicone is its radiation resistance because it is no better than in organic rubbers. Fortunately, the behavior can be improved by modifying the chemical structure of the silicone (adding phenyl groups). With that, silicone rubber can be used in cables and connectors in nuclear power plants; the modification in the structure can lead to improvements in heat resistance, properties of electrical insulation, flame retardancy and chemical resistance.

Vibration Absorption

The vibration absorption can be evaluated using the loss modulus (tan d)*. Unfortunately, the value of the silicone rubber makes them unsuitable as a vibration insulator. For that reason, the formulation must be modified. When the performance is enhanced, the behavior will be almost constant between -50°C and 100°C.


Silicone rubbers are chemically inert and they do not corrode other materials. As a result, they can be used in fixing and printing rollers.


Silicone rubber affects living tissues to a lesser extent than in organic polymers. Because they are physiologically inert, they can be used in baby bottle nipples and stoppers in medical applications. Additionally, they are adequate enough to increase the feeling grade (pleasant to the touch) so they are used in swimming caps and goggles, for example.

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