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Silicon Rubber :-
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Silicone rubber is a rubber-like material composed of silicone — itself a polymer — containing silicon together with carbon, hydrogen, and oxygen. Silicone rubbers are widely used in industry, and there are multiple formulations. Silicone rubbers are often one-part or two part polymers, and may contain fillers to improve properties or reduce cost. Silicone rubber is generally non-reactive, stable, and resistant to extreme environments and temperatures from -55°C to +300°C while still maintaining its useful properties. Due to these properties and its ease of manufacturing and shaping, silicone rubber can be found in a wide variety of products, including: automotive applications; cooking, baking, and food storage products; apparel such as undergarments, sportswear, and footwear; electronics; medical devices and implants; and in home repair and hardware with products such as silicone sealants.
During manufacture heat may be required to vulcanize (set or cure) the silicone into its rubber-like form. This is normally carried out in a two stage process at the point of manufacture into the desired shape, and then in a prolonged post-cure process. It can also be injection molded.
Silicone rubber offers good resistance to extreme temperatures, being able to operate normally from -55°C to +300°C. At the extreme temperatures, the tensile strength, elongation, tear strength and compression set can be far superior to conventional rubbers although still low relative to other materials. Organic rubber has a carbon to carbon backbone which can leave them susceptible to ozone, UV, heat and other ageing factors that silicone rubber can withstand well. This makes it one of the elastomers of choice in many extreme environments.
Compared to organic rubbers, however, silicone rubber has a very low tensile strength.[1] For this reason, care is needed in designing products to withstand even low imposed loads. Silicone rubber is a highly inert material and does not react with most chemicals. Due to its inertness, it is used in many medical applications and in medical implants.
Polysiloxanes differ from other polymers in that their backbones consist of Si-O-Si units unlike many other polymers that contain carbon backbones. One interesting characteristic is an extremely low glass transition temperature of about -127˚C (Fitzpatrick 1999:428). Polysiloxane is very flexible due to large bond angles and bond lengths when compared to those found in more basic polymers such as polyethylene. For example, a C-C backbone unit has a bond length of 1.54 Å and a bond angle of 112˚, whereas the siloxane backbone unit Si-O has a bond length of 1.63 Å and a bond angle of 130˚.
The siloxane backbone differs greatly from the basic polyethylene backbone, yielding a much more flexible polymer. Because the bond lengths are longer, they can move further and change conformation easily, making for a flexible material. Polysiloxanes also tend to be chemically inert, due to the strength of the silicon-oxygen bond. Despite silicon being a congener of carbon, silicon analogues of carbonaceous compounds generally exhibit different properties, due to the differences in electronic structure and electronegativity between the two elements; the silicon-oxygen bond in polysiloxanes is significantly more stable than the carbon-oxygen bond in polyoxymethylene (a structurally similar polymer) due to its higher bond energy.
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Mechanical properties |
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Hardness, shore A |
10–90 |
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Tensile strength |
11 N/mm² |
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Elongation at break |
100–1100% |
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Maximum temperature |
+300°C |
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Minimum temperature |
-120°C |
Once mixed and coloured, silicone rubber can be extruded into tubes, strips, solid cord or custom profiles according the size restrictions of the manufacturer. Cord can be joined to make O-rings and extruded profiles can be joined to make seals. Silicone rubber can be moulded into custom shapes and designs.
Becoming more and more common at the consumer level, silicone rubber products can be found in every room of a typical home. From automotive applications; to a large variety of cooking, baking, and food storage products; to apparel, undergarments, sportswear, and footwear; to electronics; to home repair and hardware, and a host of unseen applications.
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