In the mid-20th century, the DuPont company successfully synthesized one of the most sought-after materials in the aerospace and automotive industries. The success of this material was seen in World War II in the manufacture of gaskets and aircraft O-rings. Later, a spin-off of DuPont, the Chemours company, commercialized it under the trademark Viton rubber.
What is Viton Rubber?
Viton is a brand name of a material in the fluoroelastomer category of synthetic rubbers. As you continue reading, you will learn more about these fluoroelastomers and in particular, Viton rubber.
Like all rubbers, Viton is a polymeric material. The only difference is that this polymer is synthesized artificially, and its molecular composition contains fluorine atoms. Besides, the fluorine atoms are responsible for the major properties of Viton. Its chemical description, fluorinated hydrocarbon, is based on this characteristic.
Viton rubber is known as a high-performance fluoroelastomer because of the fluorine atoms. Fluorine is responsible for improving the inertness of the material. This is why one of the major uses of Viton is making fuel seals for aircraft and automotive.
Understanding fluoroelastomers (FKM)
Typically, you would need to learn a bit about fluoroelastomers for you to understand why Viton is so capable and reliable.
The term fluoroelastomer is formed by two names; fluoro and elastomer. Fluoro is a combining form derived from the name fluorine. On the other hand, elastomers are chemical compounds that exhibit elasticity properties after curing. Silicone is a good example of an elastomer.
With this in mind, you can deduce that a fluoroelastomer is an elastomer that has a fluorine atom in its molecular structure.
Technically, the presence of fluorine is found in the monomers making up the elastomer. Fluorine is a chemical element that is classified as a halogen. In its standard condition, fluorine is a toxic gas but it can be contained.
Characteristics of fluoroelastomers
For the most part, the characteristics of fluoroelastomers are influenced by the properties of fluorine atoms. As an example, the presence of fluorine is the main reason fluoroelastomers are extremely polar.
Polar compounds have an uneven distribution of electrical charge. Fluorine is considered a very electronegative element. As such, it means that fluorine has a strong attraction toward electrons. The ability to pull electrons from other elements makes fluorine-based compounds create strong bonds with high electron density. These attributes make Viton rubber strong.
Another characteristic of fluoroelastomers is that they swell when in contact with ketones and ethers. Also, steam can have diverse effects on the properties of Viton rubber. These features limit the usage conditions of the material.
Finally, other terms used to describe Viton rubber are FKM and FPM. These are what are known as common or trade names. Therefore, the base material and its chemical name across the industry remain as fluoroelastomers. One reason for this is that different rubber manufacturers have different ways of synthesizing the material.
Viton rubber as a fluoroelastomer
Viton is made of carbon-fluorine bonds. The presence of carbon in this material implies that the monomers of Viton polymer are organic compounds. Organic compounds are better for the environment since they are biodegradable. However, Viton is not easily degradable since the fluorine backbones protect it from other elements.
The base monomer in Viton rubber is vinylidene fluoride. This compound contains fluorine, carbon, and hydrogen atoms. Vinylidene fluoride is the generally known base monomer. Most Viton rubber manufacturers do not disclose other monomers, additives, and fillers used to make this material. These are considered trade secrets.
Other classes of fluoroelastomers
Apart from FKM, there are other classes of fluoroelastomers. The classification is made based on fluorine content, copolymer composition, and base monomers. These classes of fluoroelastomers also have different brand names. The most common classes of fluoroelastomers are FEPM and FFKM.
- FEPM– This elastomer is synthesized by the copolymerization of tetrafluoroethylene and propylene monomers. The common name for this fluoroelastomer is Aflas. It has superior properties such as resistance to steam, amines, esters, and bases. Most rubbers are not able to withstand these elements.
- FFKM – The fluorine content of FFKM is usually above 70%. This is higher than what Vitron started with. Luckily, the higher the fluorine content, the better the resistance properties of the material. FFKM is a synthetic rubber material also known as perfluoro elastomer.
FEPM and FFKM are better classes of fluoroelastomers than FKM. They exhibit excellent properties that would make them preferable to FKM. However, the properties of FKM (Viton) are sufficient to handle most environmental conditions, regardless of how harsh.
Characteristics of Viton Rubber
Fluorine atoms present in Viton give this rubber unmatched properties. Its chemical and physical properties supersede other types of rubber. Some of these properties include;
Low outgassing properties
This property is associated with materials that have a high molecular density of superior elements such as fluorine.
Outgassing means the release of gasses when exposed to certain conditions. Therefore, when a substance has low outgassing properties, its ability to release these volatile elements is limited, which is a good thing.
Since fluorine gas is toxic, low outgassing is quite helpful. This property ensures that the material does not release this and other harmful substances into the environment. This is why you will find that the FDA has approved Viton rubber for making food and related products from this material.
On top of this, low outgassing properties are helpful because they make Viton rubber applicable in vacuum situations. It also means that the material can reduce the risk of contamination in harsh environments.
Low-temperature range than silicones
The temperature range of Viton is lower than that of silicone. This means that Viton is limited to a small range of temperatures in which it can function and retain its properties.
Still, Viton is still quite thermally stable. This means that it can sustain high temperatures without breaking. The temperature range of Viton is about -20 to 250 °C. Within this range, the material remains usable. It therefore means that Viton can be used in low and high-temperature environments.
On the other hand, silicone has a higher temperature range. In conditions with temperatures ranging from -60°C up to +230°C, silicone remains. This means that products from this material can sustain freezing and sweltering conditions.
The high-temperature range is a required characteristic for most applications of these high-performance elastomers. This means that silicone can be preferred to Viton in some applications where thermal stability is required.
Difficult to Process
The synthesis of Viton rubber is technically challenging for various reasons. However, this does not mean that it cannot be processed or that there will be any problems. The only way to solve this is to ensure that the right equipment, skills, and materials are used in the manufacturing process.
One of the major challenges of processing Viton is that it becomes less viscous in the mix cycle with an increase in heat. This can pose several challenges for small-scale manufacturers. Provided, there are few rubber manufacturers who synthesize Viton. The others just purchase the material in its milled form and use it to make Viton products such as seals and gaskets.
Synthesis of Viton Rubber
Viton rubber is processed through the copolymerization of Viton monomers, which are fluoride-based. Copolymerization is simply the polymerization of different monomers to form a polymer. In this case, hexafluoropropylene and vinylidene fluoride are used to make the copolymer.
Currently, the Viton rubber being produced differs from what was commercialized and popularized in the 1950s. Chemours is the only company that produces and sells this type of fluoroelastomer as Viton. However, there are other companies that use the base monomers and add other additives and fillers to make a similar material.
Generally, the copolymerization of these monomers is the same as what other synthetic polymers go through. Essentially, it is a process that starts with initiation, followed by propagation, and finally termination. Throughout this process, there are control measures including testing, adding and removing elements, and so on.
- Initiation stage. In this stage, the fluoride-based monomers are mixed. Most of these monomers exist in gaseous states, so they are mixed in a gas chamber. This allows for a complete reaction and also prevents the gas from escaping.
- Propagation stage. This is the stage where the accelerators, processing aids, fillers, and curing agents are added. These elements are there to initiate the polymer chain formation between the base monomers. Additionally, technicians adjust the content of these additives to control the final properties of the material.
- Termination stage. In this stage, the processed material is extruded using an extruder machine. The extruder uses pressure and temperature to push the latex through a die to a vulcanizing chamber. Vulcanizing of Viton can be done using steam, salt, or via an autoclave.
These processes can change depending on the manufacturing standards of the Viton producer. In most cases, some companies use proprietary methods that are not available to the public to manufacture these materials. Therefore, our knowledge of how Viton rubber is manufactured could be limited.
Types of Viton Rubber
According to the Chemours Company, Viton’s main producer, there are four types of Viton rubber. These types are differentiated based on the material’s ability to resist specific fluids. This resistance is influenced by the amount of fluorine content in the polymer compound.
Different fluoro-monomers have different levels of fluorine in them. As such, the type of monomer used will influence the final level of fluorine. Additionally, the additives used in the propagation stage also have an influence on the level of fluorine in the material.
The four types of Viton rubber according to this classification are type A, B, F, and ETP.
- Type A – These polymers are the most common and widely used. They are also known as simply Viton A. They are known to have a faster cure rate, lower viscosity, and improved compression set and tear resistance.
- Type B and F – These types fall in the same category since they are quite similar in terms of properties and use cases. Generally, they have better processing properties, increased resistance, and generally excellent properties. In short, they are a better version of the type A Viton.
- Type ETP – This is the most advanced type of Viton rubber, also known as Viton Extreme. As the name suggests, this type has more advanced properties, better than types A, B, and F. Due to these extreme properties, this material is used to make products that are used in extreme situations.
Grades of Viton Rubber
When it comes to grading Viton, the approach used is quite different from that of classification based on fluorine content. Grading considers mostly the application and use cases of the material in relation to the specific industry. In other words, does the material meet the set conditions required for materials used in say the food industry?
From this classification, we get two primary grades of Viton; Viton GFLT and Viton A, FDA.
- Viton A FDA Sheet –This is a grade chosen from the first type of Viton. As you already know, the FDA is an organization responsible for regulating products that are used in the food and Drug industries. The Viton A FDA sheet has been cleared for use to make kitchenware and other products in these two industries.
- Viton GFLT T-600S – This grade of Viton has a 67% fluorine content. It is a peroxide-cured Viton fluoroelastomer used for general applications. The manufacturer demonstrated superior properties of this grade of Viton.
Why is the Processing of Viton Rubber Challenging
Among most synthetic elastomers, Viton is the most challenging to synthesize. There are challenges associated with the whole process. However, these challenges can be averted by optimizing the synthesis procedure.
While there are challenges, it is also worth noting that manufacturers are constantly researching and finding solutions to make Viton rubber processing less challenging. For instance, some of the types of Viton, that is B, F, and, ETP are less challenging to produce.
High Melting Point
Due to its extreme thermal stability, Viton is hard to melt. This is a challenge because it means more energy is required to melt the material. The melting point of Viton could be as high as 220°C or 428°F. Most conventional rubber molding methods such as compression molding cannot produce these temperatures. Consequently, it means specialized equipment is required.
Requires Specialized Equipment
Since machines such as compression molds are incapable of melting the material, Viton needs to be processed using specialized equipment. These equipment are designed specifically to handle the high temperature and pressure required to melt the material. The Extruder is the commonly used Viton processing machine.
The term moldability means the ability to form shapes from the material using molding techniques. Its high viscosity, melting temperature, and limited flow characteristics are responsible for this limitation. Also, this limits the formation of intricate details thereby limiting Viton to specific use cases where the product does not have intricate details.
It Takes a Long to Cure
The time it takes for a compound to cure dictates a lot about the final product. For one, it could have implications on the final cost of the product. Secondly, it could affect the productivity of the manufacturer. Viton is known to take longer to form cross-links, something that can increase production costs and time.
Viton is among the most expensive synthetic rubbers in the market. This high cost is due to the fact that this material has superior quality. Also, the intricate synthetic process increases the cost of the final product. However, you should not be concerned about that since the cost of Viton rubber is justified based on the properties of the material.
Properties of Viton Rubber
Earlier, we discussed the characteristics of Viton rubber. The characteristics are general features of the material and how it behaves. On the other hand, the properties are specific and they help you understand the material more comprehensively. These properties are usually physical and chemical. Some of the common properties of Viton rubber include;
High Resistance to Chemicals
Most inert chemicals are quite reactive. For instance, strong acids and bases can corrode the surface of the material or completely dissolve it. Such materials cannot be used in places where there is a high content of these chemicals.
Viton is considered inert. This means that it is non-reactive and hence it cannot be affected by these reactive chemicals. Most of the fuels contain reactive elements that would otherwise destroy a reactive material.
High Thermal Stability
Thermal stability is the ability of a material to withstand both low and high temperatures for extended periods without experiencing any damage.
With a temperature range of about -20 to 250 °C, Viton is quite stable in hot and cold temperatures. This is important since it means that the material can be used to make products for different environmental conditions.
Resistant to a Wide Range of Fluids
Fluid resistance is a chemical property of Viton. This material is considered inert in nature. That means it does not easily react even with the most lethal chemicals. This is why Viton rubber is used across industries where these corrosive fluids are inevitable.
Low Liquid and Gas Permeability
Permeability is the ability of molecules to penetrate material. Viton has a low tolerance to penetration by most gasses and liquids.
The permeability of Viton rubber is low because the molecular structure has fluorine. In other words, the chemical composition and molecular structure of the material are responsible for the low permeability issues. Do you remember the low outgassing properties of Viton we discussed? It is somewhat the same thing.
If you are looking for material for use in harsh outdoor environments, high weather ability is one of the properties you should consider. Weatherability means that the material can sustain UV radiation and ozone without degrading. Most materials discolor, break, or lose surface texture when exposed to these radiations.
Excellent Mechanical Properties
Tensile and tear strength, compression set, and elongation are some of the most important mechanical properties desired for rubber materials.
Viton has demonstrated to have an excellent compression set. It does not deform or lose any mechanical properties as a result. Also, the cured form of the material has a high tensile strength and tear strength.
Industries Where Viton Rubber Is Used
The properties of Viton make it usable across various industries. As a premium rubber material, Viton is used in applications where the best properties of rubber are desired. Also, these industries have huge expenditure budgets for their materials.
Viton is used in the aerospace industry to manufacture aircraft parts. Specifically, it is used to manufacture sealants, o-rings, and gaskets. These components are expected to have excellent sealing properties.
Same as in the aerospace industries, Viton is used in the automotive industry to manufacture seals, gaskets, and o-rings. The conditions in an automobile could be different from an aircraft, but there are similarities. For instance, both are high-energy and temperature conditions. As such, the rubber material has to have high thermal stability.
Oil Refinery and Chemical Processing
We saw that fluorine is an excellent element when it comes to resisting most chemicals. In oil refiners and chemical plants, you would expect to find these chemicals. Therefore, non-reactive substances are required for safety reasons. Viton rubber is used to make seals, gaskets, and hoses used in these conditions.
As a superior fluoroelastomer, Viton rubber plays a crucial role in the rubber industry. This is evident from its properties, characteristics, and use cases. This in-depth article has covered everything you would need to know about this material. Now, you are more equipped to make decisions concerning Viton rubber.