Viton rubber - FKM rubber - definition, types, properties, applications

What is Viton rubber?

Viton rubber is a type of synthetic rubber and fluoropolymer elastomer that is commonly used in O-rings, seals and gaskets. However, the term also refers to a broader family of fluorocarbon-based materials that contain vinylidene fluoride as a monomer.

Viton was originally developed and patented by DuPont, but is currently owned by Chemours.

It is very durable and resistant to harsh working conditions, including high temperatures and contact with chemicals. It also features a higher price compared to neoprene or nitrile elastomers.

Viton rubber can be easily divided into different classes based on chemical composition, fluorine content or crosslinking mechanism. Each of these factors affects the properties of the final material.

Is Viton a natural rubber?

No, Viton is not a natural rubber. It is a synthetic material that is created by copolymerising fluorinated rubber monomers.

What does FKM and FPM stand for?

The abbreviations FKM and FPM mean the same thing as Viton because they refer to the same material. The difference in name is because the different terms refer to different technical standards.

FKM refers to the American standard (ASTM), F stands for "Fluoro"; K is an abbreviation for the German word "Kohlenstoff," meaning carbon; and M is the ASTM designation for saturated skeleton rubber.

FPM, on the other hand, is an abbreviation for "Fluorinated Propylene Monomer" and refers to the international registration standard ISO 9000 and ISO/TS 16949 for fluoroelastomers

How is Viton rubber produced?

Viton rubber is produced in 3 common ways:

• Diamine crosslinking, 
• Ionic crosslinking, 
• Peroxide crosslinking.

Diamine crosslinking using blocked diamine

In the presence of alkaline (alkaline) media, VDF is susceptible to dehydrofluorination, allowing diamine to be added to the polymer chain. Typically, magnesium oxide is used to neutralize the resulting hydrofluoric acid and convert it to magnesium fluoride and water.

Although rarely used nowadays, diamine curing provides excellent rubber-to-metal bonding properties compared to other crosslinking mechanisms. Unfortunately, diamine's ability to hydrate makes diamine crosslinking sensitive in aqueous environments.

Ionic crosslinking (dihydroxyl crosslinking)

Ionic crosslinking is the next step in the curing of Viton rubber. This is currently the most popular chemical process for producing Viton.

It provides excellent heat resistance, better hydrolytic stability and better compression bonding than diamine curing.

Unlike diamino curing, the ionic mechanism is not an addition mechanism, but an aromatic nucleophilic substitution. Aromatic compounds are used as a crosslinking agent, and quaternary phosphonium salts are usually used to accelerate the curing process.

Peroxide crosslinking

Peroxide crosslinking was originally developed for FKM rubber with the addition of PMVE. This is because diamine and bisphenol crosslinking systems can lead to cleavage of the backbone chain of a polymer that contains PMVE.

While diamine and bisphenol crosslinking are ionic reactions, peroxide crosslinking is a free radical mechanism. Although not as thermally stable as bisphenol crosslinking, it is usually the best solution for aqueous and non-aqueous electrolyte media.

What materials is Viton made from?

Viton is formed from vinylidene fluoride, hexafluoropropylene and tetrafluoroethylene. Depending on the type, it may also have other additives.

What are the types of Viton rubber?

Examples of Viton rubber types are:

• Viton A - Acts as a universal seal resistant to fuels and mineral lubricants. It consists of vinylidene fluoride (VF2) and hexafluoropropylene (HFP). The fluorine content of the mixture is about 66%.
• Viton B - It is used in chemical plants and as an electric power seal. It is formed from vinylidene fluoride (VF2), hexafluoropropylene (HFP), and tetrafluoroethylene (TFE). The fluorine content of the mixture is about 68%.
• Viton F - Suitable for use with oxidized automotive fuels, concentrated aqueous organic acids, water, and steam. Like Type B, it is formed from VF2/HFP/TFE terpolymer. The fluorine content of the mixture is about 70%.
• Special types of Viton (GLT, GBLT, GFLT) - Provide the best performance in terms of fluid resistance and remain flexible at low temperatures. They contain a copolymerized monomer of fluorinated vinyl ether. 
• Viton Extreme - Is a copolymer of ethylene, tetrafluoroethylene (TFE), and perfluoromethylvinyl ether (PMVE). It shows the same great resistance to acids and hydrocarbons typical of A, B, and F types. However, in addition, it features resistance to low-molecular esters, ketones, and aldehydes. In addition, it is inherently resistant to alkali attack, and thus insensitive to volumetric swelling and loss of properties in highly caustic solutions and amines.

The main differentiating factor between Viton rubber types is resistance to liquids and chemicals, which is based on the level of fluorine in the polymer. This property is determined by the type and relative amounts of monomers that make up the polymer.

The general rule of thumb is that fluid resistance improves as the fluorine level increases. But then the material's flexibility at low temperatures also decreases. Therefore, special versions of Viton have been developed to offset this weakness.

Choosing the right type of FKM rubber for your application will depend on your individual needs, such as:

• Resistance to amines or caustics, 
• Resistance to hydrocarbon liquids, 
• Low-temperature flexibility (ability to maintain a seal at low temperatures).

What is the difference between Viton A and B?

The main difference between Viton A and B relates to fluoride content and construction. Type B contains more fluorine, so it offers better resistance to fluids and chemicals, and it also retains its flexibility better after high-temperature ageing. However, Viton A has the advantage of being more flexible at low temperatures.

What are the properties of Viton rubber?

The most important properties of Viton rubber are:

• Resistance to a greater variety of fluids and chemicals than any other non-fluorinated elastomer. Excellent resistance to oils, fuels, lubricants and most mineral acids.
• Extremely low permeability to a wide range of substances, including particularly good performance in oxygenated automotive fuels. 
• Resistance to aliphatic, aromatic hydrocarbons that dissolve other rubbers. 
• Extremely good compression resistance, even at high temperatures.
• Extremely good resistance to atmospheric oxidation, sun and weathering.
• Excellent resistance to fungi and mold.
• Good electrical properties in low-voltage and low-frequency applications.
• Low flammability; inherently more resistant to combustion than other non-fluorinated hydrocarbon rubbers.
• Resistant to temperature extremes (keep reading to learn more).

Does Viton absorb water?

Yes, Viton can absorb water. According to an article on ResearchGate, Viton can absorb water vapour to the extent of 0.1% of its weight at room temperature and 50% relative humidity. However, it should be noted that this is a relatively small amount of water absorption and does not significantly affect Viton's performance in most applications.

Is Viton stretchable?

Yes, Viton is stretchable. According to the mechanical properties of Viton listed on the Chemours website, the material has an elongation percentage of 100 to 500. This means that it can stretch up to 500% of its original length before it breaks. Keep in mind, however, that the stretchability of Viton can vary depending on the specific composition and application

What is the temperature range of Viton rubber?

The temperature range of Viton rubber extends from -45°C to as high as 316°C. However, it should be noted that the higher the temperature, the shorter the material can stay in it.

Viton compounds remain essentially flexible indefinitely when aged in a laboratory oven at temperatures up to 204°C or intermittent exposure up to 316°C. High-temperature limits are as follows:

• 3000 hours at 232°C; 
• 1000 hours at 260°C;     
• 240 hours at 288°C; 
• 48 hours at 316°C.

As for the cold, Viton's performance depends on the type of compound. Serviceability is up to -31°C in dynamic seals and -45°C in static seals using Viton GLT-S.

Is Viton suitable for hot water?

Yes, Viton is usually suitable for hot water. However, consider that regular (cheaper) FKM rubber is hardened with bisphenols and also contains calcium hydroxide and magnesium oxide as acid acceptors. This type of polymer is affected (usually softening) by hot water and steam. Nevertheless, degradation does not occur easily - it requires high temperatures and longer exposure times.

What are the applications of Viton rubber?

Viton rubber applications cover many industries and use cases. This is because it is a highly versatile material with unique properties.

Its exceptional performance in extreme temperatures, resistance to chemicals and fluids combined with its low compression ratio and good mechanical properties make it a reliable and durable option for rubber gaskets, seals, O-rings and other critical components.

Understanding the full range of Viton's uses and applications allows you to fully appreciate its value and potential. Therefore, below are some of the most common applications for rubber:

What are the applications of Viton rubber in aerospace?

Viton fluoroelastomer rubber is used in aircraft engine seals and other critical aerospace components because of its excellent resistance to high temperatures, aggressive chemicals and low compression set.

What are the applications of Viton rubber in the automotive industry?

The automotive industry uses Viton fluoroelastomer rubber for a range of applications, including fuel system seals, gaskets and O-rings. The material's resistance to fuels, petrochemicals and oils makes it extremely popular in this sector.

What are the applications of Viton rubber in chemical industry?

Viton's exceptional resistance to chemicals, acids and corrosive liquids makes it an ideal material for use in the chemical industry. It is commonly found in seals and gaskets for chemical processing equipment, as well as in tubing and chemical hoses in chemical transfer applications.

What are the applications of Viton rubber in the pharmaceutical industry?

Viton fluoroelastomer rubber is also used in the pharmaceutical industry for seals and gaskets, as well as tubing and rubber hoses in drug delivery systems.  Its chemical resistance and low compression ratio make it an ideal material for sterile processing and other critical applications.

What are the applications of Viton rubber in oil and gas industry?

In the oil and gas industry, Viton fluoroelastomer rubber is one of the most widely used elastomeric materials.

This is due to the rubber's high resistance to temperature and chemicals, making it suitable for seals, gaskets and other components used in drilling and production equipment, as well as pipes and fuel hoses in oil and gas transmission applications.

What are the trade names of Viton rubber?

The trade names of Viton rubber are as follows:

• FKM, 
• FPM,
• Dai-El, 
• Dyneon, 
• Tecnoflon,
• Elaftor,
• Fluonox.

Many of the above names originated with companies that also produce fluoroelastomers.

Who invented Viton rubber?

Viton rubber was invented and patented by DuPont in the 20th century. However, the history of the material begins much earlier.

In 1802, Éleuthère Irénée du Pont de Nemours founded a company that initially produced black powder. It is interesting to note that his father was Pierre Samuel, personal secretary to Stanislaus Poniatowski and a long-time member of the National Education Commission.

The city where the DuPont company was born was Brandywine Creek in the United States. Throughout the nineteenth century, the company invested in the chemical market, but it was not until the twentieth century that it saw its true glory. It was then that scientists working on behalf of DuPont invented highly durable materials, including:

• Teflon,
• Kevlar, 
• nylon.

Viton rubber was also one of them. DuPont sparked a real revolution in the polymer materials market.

Is Viton PTFE?

No, Viton is not PTFE. Viton is a thermosetting elastomer, while polytetrafluoroethylene (PTFE) is a thermoplastic. Both are fluorinated materials, meaning they consist of carbon atoms surrounded by fluorine atoms, giving them amazing chemical resistance However, there are clear differences between the two.

Viton offers better temperature resistance, but performs worse than PTFE in terms of chemical resistance.

How does Viton differ from EPDM?

Viton differs from EPDM in its properties. Although both materials are synthetic rubbers, Viton has greater chemical and temperature resistance. However, it is also more expensive than EPDM.

Which is better: Viton or silicone?

Viton is better for applications requiring resistance to high temperatures and chemicals, such as aerospace and industrial equipment exposed to harsh working conditions. On the other hand, silicone is a good choice when resistance to water, hydrocarbons, and low-temperature flexibility are important (e.g. in the food and pharmaceutical industries).

What are the disadvantages of Viton rubber?

The disadvantages of Viton rubber are as follows: poorer performance at low temperatures compared to other polymers, limited resistance to certain chemicals (ketones, amines, low molecular weight esters and ethers, nitro hydrocarbons and hot hydrofluoric or chlorosulphonic acids), and a higher price.

Consider, however, that some special varieties of Viton eliminate some of the disadvantages of the basic rubber version.