Silicone rubber - MVQ rubber - definition, types, properties, applications

What is silicone rubber?

Silicone rubber is an elastomer composed of silicone, which is a polymer containing silicon along with carbon, hydrogen and oxygen. It is widely used in industry, so there are different formulations for its production.

Silicone rubbers are often one- or two-component polymers and may contain fillers to improve properties or reduce costs.

This makes MVQ rubber a unique type of rubber. It has enough strength to be used in jet engines, yet provides a high enough level of safety to be used in baby bottle teats.

Silicone rubber is generally non-reactive, stable and resistant to extreme conditions and temperatures.

Is silicone the same as rubber?

Silicone is not the same as rubber. Although both materials are elastomers and show viscoelastic properties, they differ in atomic structure and have different characteristics.

Is silicone rubber a plastic?

Silicone rubber is a synthetic polymer that is often considered a type of plastic. However, it is not a traditional plastic made from petroleum-based materials like most plastics. Instead, silicone is made from silica, which is derived from sand, making it a more natural material than most plastics.

Technically, silicone can be considered part of the rubber family, but it is also a hybrid of a synthetic rubber and a synthetic plastic polymer. Therefore, silicone is neither exactly a plastic nor a rubber, but rather a unique material that shares some properties with both.

What does VMQ and MVQ stand for?

The abbreviations VMQ and MVQ stand for "Vinyl Methyl Silicone" and "Methyl Vinyl Silicon", which is practically the same thing. Both refer to silicone rubber, and a polonised version would read "poly(methyl siloxane) with vinyl groups".

How is silicone rubber produced?

To produce silicone rubber, silicone is first needed. It is formed when silicon atoms isolate themselves from silicon dioxide (silica).  This effect is achieved by heating large quantities of quartz sand to extremely high temperatures, often as high as 1800°C.

There are then several processes in which the silicon is combined with methyl chloride and heated. It is finally distilled into a polymerised siloxane known as poly(dimethylsiloxane).

The poly(dimethylsiloxane) can then be further polymerised. This is done using different techniques depending on the application of the final product.

The crude silicone compound is combined with any additives, such as pigments and catalysts. It then goes through injection moulding, extrusion, or into a 3D printer.

Curing is the final step in the manufacturing process. It takes place using one of four systems:

• platinum-catalysed curing, 
• condensation curing, 
• peroxide curing, 
• oxime curing

What are the types of silicone rubber?

The most common types of silicone rubber are as follows:

• RTV silicone, 
• Liquid silicone,
• Fluorosilicone,
• HCR.

You can read more about them below.

RTV silicone

Silicones that do not require heat to cure to their final form are called RTV (Room Temperature Vulcanising) silicones.

There are two types of RTV:

• single-component (RTV-1), 
• two-component (RTV-2).

RTV-1 silicone 

RTV-1 is available in ready-to-use form. Once applied, the stabilising agent in the silicone quickly begins to react with the moisture in the air, curing outwards.

Manufacturers use several different types of crosslinking agents. There are some that emit small amounts of acetic acid, amines or alcohols during cross-linking, while others are odourless.

RTV-1 silicones are recognised for their ease of use, good adhesion and stability at high temperatures. Typical applications include sealants, adhesives and coatings.

RTV-2 silicone 

The RTV-2 version is available in two components, which must be mixed just before use. Once mixed, it cures faster than RTV-1.

In addition, RTV-2 silicone is available in a wider range of products with excellent mechanical properties that remain constant over a wide temperature range.

Condensation-cured RTV-2 is less expensive than platinum catalyst-cured RTV-2. However, the other does not produce by-products, which is important for some applications.

Some of the countless applications for RTV-2 include 3D printing, for example, as well as coatings and moulds.

Liquid silicone

The term "liquid silicone" mainly refers to the initial stock used to create silicone products. Earlier silicone grades were supplied in a semi-solid, rubbery form that had to be press-moulded.

Liquid silicone rubber (LSR) is a two-part, platinum-cured raw material with good fluidity. This allows it to capture precise details in injection-moulded components or adapt to any surface shape as a coating.

The platinum-cured LSR crosslinking system does not produce any by-products during curing, making it a good material for food and medical applications.

Fluorosilicone

Fluorosilicone is a variant of the polysiloxane (silicone) molecule. It has the same basic silicon-oxygen chain. However, some of the methyl groups (CH3) found in the conventional silicone molecule have been replaced by trifluoropropyl groups.

This gives fluorosilicone better resistance to several troublesome environments, including:

• fuel and oil, 
• mineral spirits, 
• toluene and other organic solvents.

Fluorosilicone achieves these chemical resistance benefits while retaining almost the same mechanical properties as conventional silicone.

The only downside is that it does not perform as well in hot air and is significantly more expensive.

It is best suited to aircraft and automotive industry applications, where it is more likely to be exposed to fuel and other chemicals.

HCR silicone

HCR silicone is also referred to as "solid silicone" or "rubber compound". It consists of high molecular weight polysiloxane chains. HCR stands for High-Consistency Rubber.

HCR silicone can contain various fillers to enhance special properties such as hardness and heat resistance. It can also be cured using peroxide curing systems or platinum catalyst formulations, which produce no chemical by-products.

The material is sold in bulk form, such as rods, tubes and cylinders for further processing.

HCR is great for long-term implantable medical devices, automotive engine components and many consumer household products.

What are the properties of silicone rubber?

The properties of silicone rubber start with its incredible resistance to low and high temperatures, as well as its flexibility. The tensile strength ranges from 200 to 1,500 PSI and the maximum elongation is 700%, which is exceptionally good for rubber.

What's more, the material bounces and compresses quite well, is heat and flame resistant, and has electrical insulator qualities. In addition, it bonds well to metals.

Silicone rubber performs well outdoors due to its resistance to UV radiation, ozone and general weathering. It is also hypoallergenic and waterproof, while allowing gases to pass through, making it popular for medical applications.

Because silicone is more chemically inert than most plastics and, in addition, non-stick and non-staining, it is suitable for both consumer and industrial food and beverage applications. In sponge form, silicone rubber is lightweight while reducing vibration and noise, so it is also used in transport.

However, the material does have some disadvantages.

Silicone rubber is not resistant to prolonged contact with oils and can swell when exposed to oil or petroleum (although there are more oil-resistant varieties). Rubber is also susceptible to abrasion and tearing, and can become stiffer at higher temperatures.

Above all, however, due to its special properties silicone rubber is one of the more expensive types of rubber and is usually replaced by something cheaper when large quantities of rubber are needed.

Is silicone rubber safe?

Silicone rubber is generally considered safe for use in a variety of applications, including food contact and medical implants.  However, the quality of silicone rubber products that are available on the market varies greatly. Therefore, make sure that the particular product is made of high quality materials and used accordingly.

Is silicone rubber tough?

Silicone rubber can vary in hardness depending on its composition and application. It is available in several hardness levels, expressed as Shore A or IRHD ranging from 10 to 100, with a higher number indicating a harder compound.

Is silicone easy to break?

No, silicone is not easy to break. It is known for its durability and flexibility. Although the strength of silicone can vary depending on its grade and composition, it is generally considered a strong and reliable material for a variety of applications.

Is silicone stronger than rubber?

Silicone is more robust than rubber in terms of chemical and weather resistance. However, natural rubber tends to have higher tensile, tear and abrasion resistance. The choice between silicone and rubber depends on the specific requirements of the application.

How strong is 100% silicone?

The strength of 100% silicone varies depending on the grade and composition. While some silicone grades can be strong enough to form a strong bond, the tensile strength of typical silicone is not considered high. However, silicone rubber and 100% silicone gaskets are known for their durability and flexibility, making them ideal for a variety of applications.

Is silicone rubber elastic?

Silicone rubber is flexible. However, the exact bounce and elasticity depend on its composition. In most cases, it returns to its original shape and form without any problems.

The elasticity also depends on the hardness of the raw silicone material. However, this does not change the fact that it is suitable for various applications requiring flexibility.

Is silicone rubber renewable?

Silicone rubber is partially renewable. It is made from a material that is available in abundance (sand). However, its production requires non-renewable resources and is not widely accepted for recycling (although silicone recycling is possible).

On the other hand, its durability and suitability for various renewable energy applications make silicone rubber a useful material for promoting sustainable development.

What is the temperature range of silicone rubber?

The temperature range of silicone rubber extends from -100°C to 290°C. It is only when these standards are exceeded that it crumbles or melts. Remember, however, that the exact temperature resistance depends on the individual varieties of the material.

What are the applications of silicone rubber?

The applications of silicone rubber cover a wide range of industries. In these, it can be found on its own or in combination with other materials.

Here are the most common use cases:

• Electronics uses some of the most purified silicone rubbers for insulating tapes, sealants, varnishes, lubricants, keypads and enclosures. The thick rubber can be injection moulded into insulators and stops.
• Aircraft industry uses silicone rubber in spacesuit fabrics, tooling materials, seals and gaskets, as well as other products necessary for aircraft manufacturing and maintenance.
• Construction industry uses silicone rubber for adhesives, sealants and coatings because of its very good weathering properties and ability to bond to metal. 
• Automotive uses silicone in the form of vibration- and weather-resistant parts, as well as coatings and varnishes (but only the most heat-, oil- and fuel-resistant types are used for these purposes).
• Medicine uses special silicone rubber as a material for tubes, adhesives and antifoam agents. 
• Consumer products also contain silicone rubber. Some examples include non-stick bakeware, food containers, kitchen utensils, toys and jewellery (including bracelets). Rubber can also be used as an ingredient in shampoos, laundry soaps, cosmetics and deodorants.

It is also used in the manufacture of rubber hoses and silicone hoses.

What are the trade names of silicone rubber?

The most common trade names for silicone rubber are as follows:

• Elastoseal, 
• Rhodorsil, 
• Silastic,
• Silopren.

Who invented silicone rubber?

Silicone rubber was not invented by one man. There were many explorers behind its development, who all contributed their share to the material.

The history of silicone begins with 1824 and the Swedish chemist Jöns Jackob Berzelius. He was the first person to succeed in isolating silicon independently. Using potassium-based techniques, he extracted silicon before heating in chlorine.

This then led to vigorous combustion, resulting in silicon tetrachloride, which is used today in the production of silicones.

Although Berzelius is considered the creator of silicon, Henri Sainte-Claire Deville discovered the more common, crystallised form of the raw material 31 years later. Through an electrolytic smelting process, Deville obtained pure silicon.

Throughout the remainder of the 19th century, chemists continued their research. By the time we reached the mid-20th century, they had already developed silicone rubber for other commercial purposes.

Dr James Franklin Hyde first investigated how to produce commercial silicones in 1930.

His work combined the advantages of glass and plastics, organic and inorganic chemistry. This led to the commercial production of silicones at the Dow Corning Corporation.

However, it was a British chemist, Frederick Stanley Kipping, who named the new material silicones in 1940. He considered them to be a "sticky mess”. He failed to see the potential of silicone rubber and believed there was no practical use for it.

Of course, he was wrong, as the use of resins, elastomers and silicone rubber grew later in the 20th century. Interestingly, the silicon used in computer chips contributed to the naming of the famous Silicon Valley in the United States.

What are the disadvantages of silicone rubber?

Some of the disadvantages of silicone rubber include poor tear strength, higher cost, lower mechanical properties compared to natural rubber, limited adhesion and limited solvent resistance. However, despite these disadvantages, silicone rubber is still a versatile and widely used material.

Why is silicone rubber so expensive?

Silicone rubber is that expensive because we are talking about a specialised, high-performance polymer with unique properties. It is produced in relatively small quantities and requires expensive, complex production facilities.

High production costs (especially energy) are the main reason for the high price of silicone. In addition, silicone is only a small part of the global chemical industry and there are significant economies of scale in the petrochemical industry. In addition to this, some of the raw materials of which silicone is composed are highly scarce, which also contributes to the price increase.

Does silicone rubber contain BPA?

Silicone rubber does not contain BPA. Furthermore, it is non-toxic and suitable for the food or medical industry.