What is FKM? Things you must know about FKM/Viton?

What is FKM? Things you must know about FKM/Viton?

08/01/2019 Jon Chang Category: Blog

First of all, we should narrow it down our scope. Today we are only talk about fluorocarbon elastomers. There are two other variation of fluoroelastomer such as Fluoroalkoxyphosphazene elastomers, Fluorosilicone we are not going to discuss it today.


So let's start with the name, how to call it correctly. FKM is the ASTM designation for fluoroealstomer, "F" stands for fluoro, "K" Stands for "Kohlenstoff" Carbon in German, "M" is designation of saturated back bone rubber.

However, you might have heard FPM, it is the call out from international DIN/ISO standard.

The next common jargon is their trademark. Of course the infamous "Viton", nothing related with the fashion brand "Vuitton".

"Viton" is the register trade mark of DuPont since the invention of FKM in 1958. Since 2016, DuPont spun off Titanium dioxide product, most of fluoroproducts and some other chemicals to formed Chemours Company. Leave comments below if you want to know more in-depth story about the history.  This story is fun, I can talk it all day!

There are many fluoroelastomer makers in the world.

Such as 3M, yes! the post-it 3M produce FKM trade as Dyneon, sounds like Korean for me.

Diakin chemical produce Dai-El and Solvey specialty polymer produce Technoflon FKM.

These are the big boys in the industry.

There are many producers in the world independently produce FKM.

Here is the quick table, you can hit pause to look at it.

I will use FKM to describe fluoroelastomer in the following of my video to be precise on the description.


Fluoroelastomers enhance reliability, safety, and environmental friendliness in such areas as automotive and air transportation, chemical processing industries, and power generation. Worldwide production of fluorocarbon elastomers was about 22,000 metric tons in 2012.

Total consumption of the three major fluoroelastomers is forecast to grow at an average annual rate of 4% through 2018. Fluoroelastomers have extrodinary resistance to most fluids at high temperatures, and are replacing other elastomers in applications where improved sealing performance is necessary.

But I will give you a personal story which FKM is typically not working, Ketone.  This story I never told my advisor. When I was a graduate student, I was working on self-assembly proteins. All the petri dish, microscope slides I always wipe with acetone to remove most of the biological residue. There is one day I am going to operate a temperature controlled chamber for AFM sample, the bellow cover was made by "Viton". I checked the MSDS it just said great chemical resistance. So I wiped it with "sufficient amount" of acetone. Oh my god, the bellow lid start warping and unable to cover the fluid chamber. I was freaked out and hind the bellow from my lab member. The next day, I back to the lab this bellow return to its own shape, what a magical thing. Until I worked in the rubber industry then I resolved my mystery, because FKM will absorb ketone and swell.


Back to the main topic, we should start from it's monomers. Like most of elastomers or Rubber, FKM are polymers, which composed of multiple elastomer. There are six major monomers is used in fluorocarbon elastomer or FKM.

  1. vinylidene fluorideVDF
  2. hexafluoropropylene HFP
  3. tetrafluoroethylene TFE
  4. perfluoro(methyl vinyl ether)  PMVE
  5. Ethylene /we will use letter  E as representation
  6. Propylene we will use letter P as representation



Please refer to these two triangles The original development was a co-polymer or a dipolymer, of hexafluoropropylene (HFP) and vinylidene fluoride (VDF). Industry refer it as A-type. These included the Viton A and GA polymers from DuPont and the FL21xx grades from Dyneon. These general purpose polymers contain are 65% fluorinated and form the basis of many of the general purpose fluoroelastomers. A-type typically was cured with bisphenol AF as crosslinking agent and work with various accelerator. It so-called ionic cure. They have good resistance to hydrocarbons and good compression set resistance.


Terpolymers were developed using tetrafluoroethylene (TFE) in addition to the HFP and VDF which increase fluorine content to 68% providing improved fluid resistance but inferior compression set and low temperature performance. These materials are not usually serviceable below about -10°C. Typical materials are Viton B, FL2320 and FL2350 from Dyneon and Technoflon T838K. Most curing of these elastomers is based on the versatile bisphenol cure sys- tem, but some TFE-containing polymers are designed for free radical / peroxide curing.


Tetrapolymer fluoroelastomers growing in importance because of better low-temperature characteristics. Tetrapolymers is based on use of perfluoro(methyl vinyl ether) [PMVE] replace of HFP in copolymers with VDF and TFE. Incorporation of a small amount of cure site monomer (CSM) is necessary to facilitate curing with peroxide systems.

The fluorinated CSM improved curing and provide more stable cross-linking with increased fluorine content to 69 or 70%. The Viton GF, Dyneon FLS2650, extreme low temperature grade such as Viton GFLT. These grades have a much wider chemical resistance and can be used with methanol and a number of other polar solvents. If you have the genuine apple watch, look at it, the rubbery wrist band was made from these type of polymer.


The bloody Producer said, this topic is going too long, I should stop.

We will leave formulations, Perfluoroelastomer, TFE/P elastomer aside in the following episode. Its really too many interesting topics I want to cover.


So last important thing you need to know about FKM is what is it good for and not good at.

FKM is well know at it's high temperature resistance, it typically can serve up to 200 and 225 degrees Celsius or 392 to 437 degree Fahrenheit. Low temperature is its weakness; standard A type can operate around -15 degree Celsius or 5 degree Fahrenheit. Low temperature grade can reach -30 degree Celsius or -22 degree Fahrenheit.


Lastly, Chemical resistance. Generally speaking, most of FKM can operate in Mineral oils and greases, some phosphate esters (HFD), silicone chlorinated solvents, air and ozone, fuels. Specialty grade FKM can use in specific application which require further validation.


FKM is not working well in Steam and hot water above 100°C, phosphate esters, fuels contain methanol, gear lubricants with EP additives, engine oils with amine additives, amines, alkalis, organic acids, brake fluids and Ketones. (Acetone in my case)


The bloody producer said "That's it."


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