If you’re already familiar with polytetrafluoroethylene (PTFE), EPDM, or fluorine rubber/fluoro-rubber (FKM rubber), understanding FFKM rubber shouldn’t be complicated. Suffice it to say, FFKM rubber is everything FKM or PTFE rubber is and more—with enhanced temperature and chemical resistance.
In this guide, we’ll touch on every possible area you need to know about FFKM rubber compounds, including their properties, use cases, price, etc. By the end of this piece, we expect you to fully grasp what FFKM rubber is and what makes it better than FKM or any other rubber elastomer in the market.
What Is FFKM Rubber?
The abbreviation “FFKM” is derived from perfluoroelastomer. It’s basically a class of elastomeric rubber or fluoroelastomer originally invented in the late 60s to rival the FKM rubber. It offers enhanced properties and qualities that satisfy emerging medical and engineering needs—particularly in the mechanical sealant and pharmaceutical market.
However, there have been reports of shortages in the supply chain and distribution of FFKM rubber. These shortages have spiked interest in alternatives like FKM, EPDM/EPR, FPM/FFPM, etc. Some of the major contributors to these shortages include the coronavirus pandemic and global political and economic crises affecting countries with the right FFKM resources.
Notwithstanding, FFKM rubber compounds are still much alive in the market, thanks to trademarks like Perlast, Kalrez (DuPont, US), Chemraz, etc. You can purchase FFKM rubber products or materials from these brands and have them delivered to you within a few weeks, depending on the delivery conditions, such as location and mode of delivery.
Before forging ahead, it is important to know that FFKM compounds are used extensively in engineering and medicine to
- Make O-rings and gaskets for sealing specific areas in equipment or machines or avoid leakages or breakdowns due to friction.
- Fabricate semiconductor wafers used in manufacturing silicone microchips and ICs in electronic devices, etc.
What Is the Chemical Composition of FFKM Rubber?
The carbon-fluorine bond is the primary chemical makeup of FFKM compounds. Per chemistry, this bond is one of the strongest existing bonds. This also gives FFKM compounds their nearly inert ability and high chemical, oxidation, and heat resistance.
Diving further into the chemical composition of FFKM rubber is the percentage composition of the fluorine in it. Fluorine, the leading element in FFKM, has the highest percentage, followed by carbon. Typically, this percentage is over 70%—at least 40% in FKM (with 38-68% F) and less than 5% or more in PTFE (usually between 75-76% F).
As an elastomeric compound, carbon combines with fluorine to form symmetrical ethers with the chemical formula “R-O-R.” This is what an FFKM rubber full form looks like. In this formula, O represents the oxidizing element, which is fluorine.
On the other hand, R refers to any alkyl groups that continuously bond with the compound to form polymers or elastomers. Usually, this is done in the appropriate concentration so that FFKM rubbers do not lose their elasticity and durability during production.
Benefits and Properties of FFKM Rubber
With the chemical composition of FFKM rubber in mind, let’s look at some of its properties in detail. This should give you an insight into what FFKM benefits and its uses in mainstream engineering and medicine.
High Chemical Resistance
FFKM is reportedly resistant to over 1,800 chemicals and oxidizing agents (gasses or liquids). Other reports even say it’s resistant to virtually all chemicals, excluding fluorinated chemicals like chlorofluorocarbons or freons used in aerosols and refrigerants.
High UV Resistance
Because of the numerous vulnerabilities caused by UV rays, experts would advise you to go for UV-resistant products such as silicone and, of course, C-F compound materials like PTFE or FFKM rubber sheets. Not complying with this advice could incur more costs for maintaining
High-Temperature Stability and Steam Resistance
Although FFKM reportedly has an impressive ambient working temperature range of -50°C to +250°C (equivalent to -9.4°F to +482°F), it still offers the high-temperature stability of PTFE, which is around 320/327°C (about 620 degrees Fahrenheit).
Aside from heat resistance, FFKM rubber seals or compounds are nearly impervious to any chemical or materials. However, FFKM may be permeable under different circumstances, like temperature above its threshold or tension above normal levels. This is rare as these conditions may not occur normally or naturally.
Low Compression Set
Elastomers are rubber; as you commonly know, when you compress rubber, it returns to its original state or becomes completely deformed. This theory is called a compression set. A low compression set indicates that the material has a higher chance of returning to its original state after subjecting it to an average compression or tension under normal temperature and pressure.
Conversely, a high compression set indicates the opposite of everything a low compression set material offers. FFKM rubber compounds have low compression, making them durable and highly elastic, regardless of their thickness. In this case, it would take an over-the-limit tension or compression to transform or permanently deform them.
Excellent Compression and Tensile Strength
You can determine these two properties with a metric scale such as the Shore Hardness Scale or Durometer. You can say an elastomer or rubber is Shore A hard if the measuring scale or durometer shows a very impressive resistance to indentation. A normal FFKM compound rubber should have a Shore A hardness of around 80. This metric score indicates that the compound or material can withstand compression for up to 70 hours at 200°C.
This measurement is similar to the compression set of a shore heel on a Shore Hardness Scale Chart. On the other hand, we have the tensile strength represented as “elongation at break.” This implies the percentage stretch an FFKM rubber compound can go before exceeding its elastic limit or tensile strength. This could be between 125 and 250 percent of 10 and 20 megapascals (MPa).
Enhanced Electrical Insulation
FFKM rubber compounds have completely bonded fluorocarbons and form only single bonds. Hence, there is no space for electrons or protons to interact, leading to high insulation. The electrical insulation properties of perfluoroastomers make them a great fit for building insulators used in electrical engineering industries. Moreover, we could exploit their dielectric and semiconductive properties as well.
Polymers are organic compounds, too, and one of the known extreme properties of organic compounds is outgassing. When polymers or organic compounds outgas, they give off smells or volatile organic compounds to their surroundings. This is one of the reasons why polymers are not recommended for preserving food or edibles because they could contaminate them. However, FFKM compounds do not outgas like the other polymers or alternatives.
Strong Inertness to Several Gases and Fluids
Apart from its low outgassing properties, FFKM compounds are inert to gasses and fluids. The reason is that they do not easily bond with other compounds—liquid or gas—due to their strong covalent C-F bond. So, while other elastomers may still have low outgassing properties, they may still be able to interact with the liquid or gas they come in contact with under certain over-the-limit conditions or subjections. And this could prove disastrous in the end.
Differences Between FFKM Rubber and Other Rubbers
This is how FFKM rubber compares with other natural and synthetic rubbers like nitrile and neoprene rubber.
|Parameters for Comparison
|Little or no chemical resistance.
|Limited chemical resistance compared to FFKM or Neoprene rubber.
|Lower chemical resistance compared to FFKM rubber. It has been reported to resist more than 1,500 chemical compounds.
|High chemical resistance. It can reportedly resist any non-fluorinated chemical.
|Lesser thermal resistance than Nitrile rubber. It may deform with temperatures above 100°C.
|Lesser thermal resistance. It may deform with heat above 120°C.
|High thermal resistance up to +275°C.
|High thermal resistance. It can withstand high temperature ranges up to 327°C
|Physical and mechanical qualities
|Seals may easily creep when used in high-pressure or hydraulic engines or equipment.
|Good physical and mechanical sealing properties; not better than Neoprene or FFKM rubber.
|Excellent mechanical attributes and sealing properties.
|Displays excellent mechanical attributes and sealing efficiency
|Permeability to chemicals, gasses, steam, etc.
|It can be permeable to chemicals and steam.
|It can be permeable to chemicals and steam.
|Impervious to liquid and gasses.
|Impermeable to liquid or gasses.
|Resistance to ozone oxidation and weather conditions
|Low resistance to ozone oxidation and weather conditions.
|Limited resistance to ozone oxidation and weather conditions.
|Resistant to weather conditions or ozone oxidation.
|Resistant to weather conditions or ozone oxidation
|Working temperature ranges
|Lower working temperature ranges (typically between -48°C and +98°C).
|Lower working temperature ranges (typically between -56°C and +108°C).
|Efficient in a broad working temperature range (typically between -50°C and +275°C).
|Efficient in a broad temperature range (typically between -50°C and 327°C)
The Manufacturing Process of FFKM Rubber
We showed you the major use for FFKM rubber and why we use it to make such materials. In this section, we’ll highlight the manufacturing process of FFKM rubber compounds. Typically, FFKM rubber compounds occur as synthetic rubber or elastomers. Therefore, their production process usually follows two primary routes.
The first is the polymerization stage, and the second is the processing stage. Under these two stages, we have other processes that the FFKM rubber undergoes before becoming commercially available for use.
1. Polymerization Process
Nearly all rubbers (polymers or elastomers) undergo a polymerization process. FFKM rubber, a fluoroelastomer (or fluorinated elastic polymer), follows the same process.
Polymerization produces the continuous chain of monomers of the fluoroelastomers, which in this case are fluorocarbons. This process is usually facilitated by catalysts, additives, and processing aids like sulfur, silica, carbon black, amines, phosphates, esters, etc.
During polymerization, the unvulcanized monomer, isoprene, is subjected to different oxidizing or reducing agents under various hot (50°C) or cold temperatures (5°C) conditions. The FFKM rubber temperature range used in the polymerization process affects the type of elastomer produced—branched or linear chain elastomer.
That said, we have the emulsion polymerization and solution polymerization. In the solution polymerization, the monomer is dissolved in a hydrocarbon solvent like hexane or cyclohexane, depending on the class of polymer you want to produce—cyclic or acyclic. After dissolving the solvent, you may add a catalyst to the system and form the polymer.
The emulsion process uses liquid soap or detergent (surfactants) as solvents for the monomer. A catalyst like a peroxide or potassium salt facilitates the reaction to form the polymer or elastomer. The resulting product is coagulated, washed, dried, and taken to the processing stage.
2. Processing Stage
The processing stage involves grinding or masticating the polymerized FFKM rubber and then mixing it with additives, dyes, fillers, reactive compounds, or processing aids. Afterward, the rubber or elastomer undergoes extrusion or molding before hardening it through curing or vulcanization.
Molding or Extrusion
Molding or extrusion is the stage in which we eventually convert the FFKM compounds or elastomers into a desired shape. This stage is where we produce products like O-rings, gaskets, or stoppers. During this stage, the softened or molten FFKM rubber compound is put into an extruder machine with the designated profile, size, and thickness.
Curing and Vulcanization
After extrusion, the soft product is reduced with sulfur to become hardened through vulcanization. Curing can also be done with fluorocarbon intermediates like Bisphenol AF or hexafluoropropylene.
3. Post-Processing Stage
The post-processing stage is the point where we properly examine and test the perfluoroelastomer for outgassing or contaminants or impurities that could hamper the quality of the FFKM rubber compound produced.
Peradventure, if the product doesn’t meet the quality or standard set by legal authorities, it will be recycled and reinvented until it matches the industry standard and customer quality. The post-processing stage is subdivided into post-curing and quality control.
This is simply subjecting the FFKM material to further vulcanization to improve its physical properties or harden it further. We usually do this if it’s necessary. Otherwise, the material is pushed to the quality control center for inspection.
Quality control ensures that the product passes the necessary standards set by organizations such as the International Organization for Standardization (ISO), ASTM International, World Standards Cooperation (WSC), etc.
Types of FFKM Rubber
FFKM rubber comes in several types or analogs that depend on the production method or additive used in the process. Typically, these rubbers generally follow the organofluorine rule, which brings them under one parent chemical composition or backbone.
Nonetheless, different types of FFKM rubber could display or offer other chemical and mechanical benefits. So, unlike what we may have highlighted in this piece, some FFKM rubber compound types may exhibit lesser benefits than their universal alternatives or rivals.
With that in mind, here are the common FFKM rubber types:
1. Perfluoroether (FFKM-FFE)
Perfluoroether is one of the most commonly used perfluoroelastomers today. As an organofluorine compound, we commonly use it to make FFKM rubbers that are super resistant to aggressive chemicals. Perfluoroether’s primary distinction is the presence of one or more ether functional groups. These compounds can be cyclic, such as those containing oxygen (i.e., tetrafluoroethylene oxide and hexafluoropropylene oxide), and acyclic, which typically have lower molecular weights and more fluoride than the cyclic types.
2. Tetrafluoroethylene-Perfluoroalkyl Vinyl Ether (FFKM-TFE/PFA)
We also call this compound perfluoroelastomer alkoxy Vinyl Ether or copolymer PFA. It is an organofluorine compound similar to perfluoroether. Evidently, the presence of the ether functional group sold it out. Like perfluoroether, we use FFKM-TFE/P to manufacture thermally and chemically-resistant FFKM materials or products. It usually follows the production method of PTFE and MFEs but utilizes different molecular ratios.
3. Bisphenol AF (FFKM-BPAF)
We use this variant or analog of Bisphenol A to produce thermoset plastics or polymers. However, the determiner here is the presence of fluorine that eventually forms the carbon-fluorine bond. In the case of Bisphenol AF, the three-dimensional trifluoromethyl group replaces the two alkyl groups during production. This three-dimensionality is why BPAF is greatly used as a crosslinking agent to transform or vulcanize rubber or plastics into fluoroelastomers. It can also serve as an additive when producing some fluoroelastomer compounds.
4. Tetrafluoroethylene-Hexafluoropropylene (FFKM-TFE/HFP)
Hexafluoropropylene serves as a monomer and intermediate used in producing other organofluorine, especially PTFE and FFKM compounds. We usually mass-produce it as an oxide called Hexafluoropropylene oxide (HFPO). And just like the Bisphenol AF, it can serve as an interlinking or crosslinking agent. Usually, we produce HFP by reducing perfluoroethylene without an oxidizing agent like oxygen under controlled temperature and pressure.
5. Perfluorocarbon (FFKM-FFC)
We had to include the common perfluorocarbon. The reason is that it forms the backbone of perfluoroelastomers. Every other elastomer (with a C-F bond) mentioned in this section finds its roots in perfluorocarbon and derives its benefits from it. We don’t have to say much about perfluorocarbon, as everything you’ve read up until now explains everything you need to know about it. So, you may reference the previous sections where we discussed its chemical compositions and properties to refresh your knowledge of its concept or benefits.
Applications of FFKM Rubber
Before now, you saw some uses of FFKM rubber. Now, we’ll show you some industries where these products apply. Meanwhile, some industries listed here may use FFKM compounds or polymers as intermediates during production.
Semiconductor companies that produce silicon wafers or chips use FFKM elastomers due to their excellent resistance to aggressive chemicals and specialty gasses. These toxic acids, bases, or chemicals are used to perform surface preparations, deoxidation, and regeneration of semiconductors during production.
Furthermore, some reports claim that FFKM semiconductors offer the lowest particle and trace metal contamination. When used in macro equipment or machines, FFKM minimizes chemical erosion rates and produces lesser yield loss in these semiconductor materials.
Another area where FFKM elastomers have been effective is the outdoing of Moore’s law, which observes the doubling of transistors used in integrated circuits (ICs) every two years. FFKM elastomers provide high purity and optimized semiconductor conditions that reduce the aforementioned law or observation in the computer world.
Aircraft and space shuttles are other machines or equipment always in contact with UV radiation, high temperatures, and ozone reactivity. FFKM compounds or fluoroelastomers are super effective in this industry due to their unreactivity and heat resistance capabilities.
FFKM seals can also be used in the engine section of these aircraft and space shuttles for their elongation and tensile strength capabilities. Remember that replacing a damaged seal is quite difficult and expensive, and aerospace companies do not want to deal with that all the time. So, the best option to use is FFKM seals.
Food and Drug Processing
Food and drug processing industries, such as pharmaceutical companies, do not want to risk contaminating their products with materials that have high outgassing properties. FFKM rubber properties exhibit little or no outgassing, making it a better choice of sealing material in the machines used to test or produce these foods or drugs.
Meanwhile, other polymers or elastomers may decompose upon oxidation or chemical attacks during production processes and, in the process, contaminate the product. Another situation is heat action, forcing the seal to creep out of form and causing leakages and wastage from the machine.
Oil and Gas
Petroleum industries always require elastomeric seals in distillation equipment or sections like pump housing, reactors, mixers, compressor casings, valves, etc. The best option to withstand the high temperatures in these distillation tubes or machines is FFKM rubber due to its impressive thermal and steam resistivity.
Another case study that proves that FFKM rubber compounds would be most beneficial to the oil and gas industry is the issue of heat aging and fluid attack in the complex distillation system. These issues can cause low-resistant elastomeric seals or gaskets in these machines to break down easily.
Therefore, a cost-effective and better alternative would be FFKM seals. It’s cost-effective in the sense that you do not have to change it or buy a new one all the time when extreme conditions begin to affect the machine system.
Limitations of FFKM Rubber
FFKM may look all glamorous, especially because of its elevated advantages over other natural or synthetic elastomers. However, it has its limitations, which include:
- Difficulty in production or processing: FFKM rubber or elastomer is quite difficult to make. This is a major reason behind their different standards. The American standard is different from the German standard because of the variation in their production process.
- Very costly to produce and purchase: Not only is FFKM elastomer difficult to make, but it is also expensive. A 10 kg FFKM rubber price, if converted for other uses, could buy you an SUV or even higher-price cars. This explains why they are mostly used in specific engineering and medical fields or industries.
- Poor creep properties in fluorinated solvents and low temperatures: An FFKM rubber sheet or seal has very poor creep (deformation) properties below their working temperature ranges. Additionally, FFKM rubber tends to swell or permanently deform in fluorinated solvents.
- Poor physical properties in certain conditions: For instance, using perfluoroelastomers in molten or gaseous alkali metals or temperatures could force them to look at their physical properties or structures. This also explains their poor adaptability when a material using an FFKM seal undergoes thermal expansion; you’ll only need to replace the seal to fit the equipment or machine.
FFKM rubber compounds offer excellent and advanced advantages over other fluoroelastomers in the industries that use them. This guide highlighted all the essential areas that exposed FFKM rubber uniqueness, including its chemical composition, properties, and benefits.
We also saw that FFKM rubber is super important to silicone semiconductor manufacturing industries due to its reduced trace chemical contamination properties, temperature resistance, and durability.
Suppose you need to learn more about silicone semiconductors or how elastomers contribute to developing enhanced semiconductors or other technologically sustainable products. In that case, you may visit our product catalog or see more in our resource center.