Fluorosilicone Rubber – Properties, Processing & Engineering Applications

Silicon rubber, among other established elastomers like neoprene, continues to dominate numerous engineering applications due to its impressive properties. However, it falls short on numerous fronts, creating an insatiable demand for other elastomers, particularly fluorosilicone rubber, which boasts greater immunity against chemical fluids and fuels. Here is everything you need to know about this long-lasting elastomer that has become a mainstay in the petrochemical, aerospace, oil & gas industries.

What is Fluorosilicone (FVMQ)?

FVMQ is simply improved silicone rubber reinforced to withstand prolonged exposure to volatile solvents, oils, fuels, and chemicals, amongst other aggressive fluids. It boasts the great elastomeric properties of silicone rubber and the added chemical compatibility of trifluoropropyl groups. Additionally, fluorosilicone works well in both extremely cold and hot conditions, and it hardly loses flexibility even at low temperatures thanks to its enormous temperature range, which stretches from -60°C to +200°C.

· Chemical Structure/Elements

Fluorinated silicone rubber is essentially silicone rubber modified to facilitate its use in industries handling volatile chemicals and fuels. At its core lies siloxane, which endows it with great thermal stability and excellent UV resistance. This core, often expressed as –Si–O–Si–O–Si–, further provides this elastomer with a low glass transition temperature.

Its structure also includes side groups of trifluoropropyl (–CH₂–CH₂–CF₃), and Methyl Side Groups (–CH₃). The former is responsible for fluorosilicone’s improved resistance against chemicals and oils, while the latter eases its processability. The underlying table summarizes its key constituents and their respective roles.

Properties of Fluorosilicone for Engineering Applications

· Great Temperature Resistance

FVMQ is greatly favored in industrial processes and facilities prone to extreme temperatures, thanks to its excellent thermal stability, which it draws from its siloxane backbone. It performs optimally at temperatures as low as –60°C as well as temperatures as high as +200°C.

Unlike other hydrocarbon elastomers, it remains flexible under low temperatures and structural integrity remains intact under extremely high temperatures.  However, it starts to break down or degrade once you expose it to temperatures surpassing +200°C for prolonged periods.

· Chemical Resistance

Fluorosilicone rubber adds to its impressive thermal properties by reinforcing its chemical resistance with the addition of fluorine sub-groups. This makes it relatively more suited to applications handling hydrocarbon fluids and a host of other volatile chemicals.

It demonstrates great resistance against dilute acids and organic acids such as acetic acid. However, it can degrade when exposed to highly concentrated or oxidizing acids such as fuming sulfuric acid. Furthermore, it swells and loses structural integrity when in contact with strong bases and amines.

· Mechanical Properties

• Tensile Strength: FVMQ boasts tensile strength ranging between 7 and 8 MPa, making it ideal for distinct cushioning and sealing applications. Compared to alternative rubbers, such as nitrile, this is quite low. However, if you desire to reinforce its tensile strength, you can inject silica fillers during post-curing.
• Tear Resistance: When installing or handling components made from fluorosilicone rubber, you must exercise great caution since its tear-resistance, rated at approximately 10–25 kN/m (Die B), is relatively weak. If subjected to great force, it is likely to tear or nick.
• Hardness: With an average hardness of between 40 and 80 Shore A, fluorosilicone rubber is regarded as a relatively soft elastomer. It is, however, harder than standard silicone, explaining its extensive utilization in demanding sealing applications.
• Elongation: FVMQ can withstand relatively long stretches without deforming permanently or losing its structural integrity, thanks to its great elongation range, which extends to between 150% and 400%. Although this is essentially lower compared to standard silicon rubber, it allows you to elongate your fluorosilicone seals up to 400% without risking permanent deformity.
• Compression Set: Fluorosilicone seals retain their integrity for ages thanks to the exceptional compression set of FVMQ, which stands at 15-30%. This means that components made from this elastomer rubber can tolerate extreme compression forces before breaking down. However, when compressed at temperatures starting at 175°C for over 22 hours, you risk deformation.

· Weather Resistance

Fluorosilicone rubber thrives in settings prone to harsh or unfriendly weather elements such as UV radiation, moisture, and high temperatures. This is because it comprises a silicone core, supplemented by fluorine and methyl sub-groups, which makes it resistant to cracking and atmospheric aging when exposed to these harsh weather elements. As such, you can deploy it in outdoor spaces without having to worry about its longevity.

· Durability

The impressive thermal stability of FVMQ, coupled with its reinforced resistance against chemicals and fuels, generally translates into a longer operational lifespan. When utilized in settings exposed to favorable weather and operational conditions, FVMQ components can serve you diligently for up to 25 years. However, if the conditions are relatively harsh, this lifespan may drop to around 15 years.

· Gas Permeability Resistance

The inclusion of trifluoropropyl groups in FVMQ contributes to its compact molecular structure, making it up to 10 times more gas permeability resistant than regular silicone rubber. However, its resistance to gas permeation comes second to other elastomers, particularly butyl and nitrile rubber.

· Insulation Properties

FVMQ makes excellent insulators, thanks to its enormous dielectric strength, especially in applications subjected to volatile chemicals or harsh conditions. Its dialectic strength is similar to that demonstrated by regular silicone rubber, averaging between 10 and 20 kV/mm, allowing its deployment as insulators in the aerospace, automotive, and defense industries.

Processing Fluorosilicone

Owing to its distinct yet impressive properties, fluorosilicone rubber is broadly exploited to fabricate numerous components that play an indispensable role in varying industries. Transforming it from raw FVMQ into functional components, however, necessitates a lot of effort and expertise in the processes discussed below.

· Compounding

Fluorosilicone is first manufactured as gum, which lacks the strength needed to fabricate rigid engineering components like seals and gaskets. Compounding turns this raw gum into a strong material that you can modify to generate components of your liking. It involves the injection and mixing of reinforcing fillers, additives, and cross-linking agents. Additives added include acid acceptors and heat stabilizers, which boost the rubber’s thermal stability.

· Injection Molding

This processing technique allows you to generate intricate yet rigid engineering pieces with great dimensional accuracy from compounded FVMQ. The compounded fluorosilicone is first softened by controlled heating, and then it is injected into designated mold cavities. The heated raw fluorosilicone is then pressurized, forcing it to assume the shape of the mold cavities before being cured, leaving you with the finished FVMQ parts.

· Extrusion

Extrusion utilizes heat and pressure to produce tubes, seals, and hoses, amongst other fluorosilicone parts, with great chemical and oil resistance. It involves rigorously mixing the core flourosilicone material with fillers and curing agents before the resulting mixture is shaped into your prescribed components. The extruded parts are then vulcanized, leaving you with high-quality FVMQ components, characterized by great chemical resistance.

· Bonding and Adhesion

FVMQ is essentially a non-stick material, meaning that bonding it to other materials, especially plastics and metals, can be quite challenging. Bonding fluorosilicone to most substrates requires the use of cross-linking agents such as peroxides and the application of heat. You must etch the workpiece you intend to merge with the fluorosilicone rubber before vulcanizing the bond with controlled heat and pressure.

How to Safely Handle Fluorosilicone Rubber

Whereas FVMQ hardly poses a serious threat to you or your health, it is advisable to be cautious when handling it. You are advised to;

• Wear your protective clothing, particularly gloves, when handling FVMQ for long periods.
• Ensure there is sufficient ventilation before processing fluorosilicone rubber.
• Keep it far from open flames.
• Store it properly.
• Handle it as per your manufacturer’s recommendations.

Comparing Fluorosilicone to Other Engineering Elastomers

Engineering Applications

Fluorosilicone not only promises the thermal stability and flexibility of silicone rubber, but it also comes with the reinforced chemical resistance of fluorine side groups. This has made it one of the most sought -after materials in industries such as;

FAQs

When was fluorosilicone rubber developed?

The origin of FVMQ dates back to the early 1950s, with Dow Silicones credited for its creation.

What is the main difference between fluorosilicone and standard silicone rubber?

Whereas fluorosilicone demonstrates most of the attributes exhibited by standard silicone rubber, it is slightly different in composition and certain features. It contains trifluoropropyl groups, which reinforce its immunity against fuels, oils, and chemicals.

What are the limitations of fluorosilicone rubber?

Despite FVMQ thriving in industrial applications demanding great chemical and fuel resistance, its suitability for applications prioritizing abrasiveness can be questioned. Its physical strength leaves a lot to be desired, and its gas permeation resistance is comparatively weaker.

Is fluorosilicone rubber safe?

Yes. The stability of fluorosilicone guarantees its safety even under extreme temperatures. However, you must exercise caution when dealing with it for prolonged periods to avert skin irritation.

What are the advantages of using fluorosilicone rubber?

Fluorosilicone rubber’s unique composition not only makes it suitable for challenging applications, but it also makes its use quite rewarding with benefits such as;

• Retained flexibility at low temperatures.
• Unrivalled chemical resistance.
• Impressive insulation properties
• Broad temperature range.

Is fluorosilicone resistant to all chemicals?

No. Whereas fluorosilicone retains its structural integrity when exposed to most chemicals and oils, it does swell or degrade when subjected to certain chemicals. This includes highly concentrated acids and strong alkalis.

Can you bond fluorosilicone rubber to metals?

Yes. Although FVMQ does not stick easily, you can merge it with different substrates, including metals and plastic, with the right bonding techniques and adhesives.

Is FVMQ suitable for continuous and high-temperature applications?

Yes. FVMQ bears the thermal stability of standard silicon rubber, which allows its continuous use at high temperatures, some as high as 200°C.

How long do FVMQ components last?

Fluorosilicone components, such as seals, can serve you for up to two decades, depending on the harshness of the operational conditions they are subjected to. Components operating under friendly conditions can serve you for over 25 years, while those operating under harsh conditions remain effective for 10-15 years.

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