Silicone rubber is an elastomeric polymer which is chemically composed of Si (silicon), O (oxygen), C (carbon), and H (hydrogen). The most commonly used silicone rubber in industry is Polydimethylsiloxane (see chemical structure image below) which is composed of a backbone of Si (silicon) and O (oxygen) molecules with CH3 methyl groups.
The methyl groups do not react easily with other chemicals and help the silicone polymer to resist chemical interaction, which aids in its stability and biocompatibility. The non-reactive nature of silicone rubber is the primary reason it is used so widely in medical and implant applications. Additionally, silicone rubber is highly stable at extreme temperatures (-55°C (-67°F) – +300°C (572°F)), which allows medical application silicone rubber parts to be easily sterilized using dry heat, autoclaving, or other sterilization processes using elevated temperatures. But due to the excellent physical properties of silicone rubber, and the ease of fabrication in molding, casting, and extruding processes, silicone is found in many different non-medical applications as well, such as food, automotive, aerospace, electronics, industrial, military, and consumer products.
Forms of Silicone Rubbers
Silicone rubber comes in a variety of different forms LSR (liquid silicone rubber), HCR (high consistency rubber), of which may be designed for curing at high temperatures (HTV: high temperature vulcanization) or cure at ambient temperature (RTV: room temperature vulcanization). It may also come as a one part, two part, or more than two part kit (depending on how much has been compounded into the material ahead of time, including inhibitors, catalysts, and colorants). The mix ratios of these kits can also very, while a 1:1 mix is fairly common, 9:1, and 10:1 also occur frequently in industry. And all of this only refers to a subset of silicone materials, there are other curing mechanisms as well that utilize moisture in the air, or even UV light to vulcanize (cure, harden) the rubber. But it is difficult to touch on everything in this relatively brief post. Additionally, this post will most likely be out of date shortly after it is uploaded, as silicone rubber is a relatively young polymer (dating back only to the 1940’s), and is ever evolving.
Historically, Dow Corning is on record for being the first produce silicone rubber, which took place in the early 1940’s. A few years later GE opened a silicone processing plant of its own (now Momentive Silicones) and Wacker Chemie also began production of silicone. Not far behind was Shin-Etsu Chemical in the early 1950’s. Presently there are different silicone material suppliers all over the world, constantly developing new materials to meet the needs of the market.