Nitrile Rubber Floats

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WZ507
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Nitrile Rubber Floats

#1

Post by WZ507 »

The topic titled "Cotton" has been "locked" so no more replies are possible there. Near the end of that topic Mr Big posed a question along the lines of "why aren't all Nitrophyl floats equivalent in terms of performance (swellability)?" to which Cotton responded that his employed genuine Nitrophyl M.

With the above as introductory context, thought some further explanation might be of interest to the forum members regarding nitrile-butadiene rubbers and their solvent/oil resistance.

Rogers Corporation Nitrophyl material is a nitrile-butadiene rubber (NBR), also known as Buna-N, which is a copolymer made from butadiene (non-polar monomer) and acrylonitrile (polar monomer). NBR is the most common rubber used in industry to provide fuel and oil resistance in a wide range of applications.

NBR rubbers are made in myriad compositions where the nitrile content can vary from a few percent up to about 50%. All other things being equal, the higher the nitrile content of the composition the more polar the rubber, and the better the fuel and oil resistance. Click on the chart at the link below to expand it and see the large variety of NBR rubbers offered by one vendor, Zeon Chemical.

http://www.zeonchemicals.com/Nipol/Prod ... ction.aspx

Another key factor that imparts solvent resistance (gasoline resistance) to NBR rubber, and all polymers, is crosslink density (x-link density). Crosslink density refers to how well a rubber is cured or vulcanized, i.e., how well the polymeric chains are bonded to one another. Depending on the application, NBR rubber may be employed as polymerized, i.e., without x-linking, or may optionally be post x-linked during subsequent processing. So why would we care if NBR was crosslinked? Because swelling of a polymer by solvent is inversely proportional to x-link density, i.e., the more crosslinked the polymer is, the less it will swell in solvent. And why do we care if a polymer swells in solvent? Because it can result in the predicament Cotton illustrated previously, where a float changed dimensions due to imbibing solvent.

In light of the above observations, to optimize fuel resistance of an NBR rubber one would desire a composition that was either high in nitrile content, or well x-linked, or both.

Although we've talked about how to optimize solvent resistance of NBR, there is one glaring omission we have yet to include in the discussion and that is the solvent system, i.e., what solvent system is the NBR (float) exposed to and expected to survive in? The link below is from Roger's Corp website and shows the resistance of an unspecified Nitrophyl NBR composition to a wide variety of solvents/solutions.

http://www.rogerscorp.com/ec/nitrophyl_ ... ility.aspx

Note how resistant the Nitrophyl rubber is to a variety of non-polar saturated hydrocarbon solvents - aviation gas, jet fuel, heptane, naptha, stoddard solvent, etc, or restated, Nitrophyl would be very resistant to old fashioned gasoline, which was predominantly saturated branched hydrocarbons. However, notice that Nitrophyl does not have good resistance to common aromatic solvents, e.g., toluene and xylene, nor does it fair well with moderately polar solvents such as acetone and MEK. Note that in the hydrocarbon section of the table there is an asterisked (*) entry for a blend of hydrocarbon with less than 10% methanol, with the comment * For higher percentage of material [methanol], we recommend our NITROPHYL-M material. This is why Cotton employs the "Nitrophyl M" product - because it is Rogers superior NBR for challenging solvent systems (present day oxygenated gasoline?). Although the exact composition of Nitrophyl M is unknown to us, if it has higher solvent resistance than standard Nitrophyl, then it is based on a higher nitrile content rubber, has a higher x-link density, or both.

Regarding present day gasoline that is more polar, due to the addition of polar molecules, e.g., alcohols, ethers, etc, it becomes a quite different and more aggressive solvent system. For example, when 10% ethanol is added to gasoline, a new solvent system is created and the solvent properties of gasoline and ethanol no longer exist in this fuel blend, but instead, a new solvent system is created that is intermediate between gasoline and ethanol in terms of polarity and solubility parameter, and is considerably more aggressive toward NBR than the parent gasoline.

It may seem surprising that such a small amount of ethanol (10% by volume) can result in such a significant shift in the solvent properties of gasoline. However, when we consider the density and molecular weight of gasoline and ethanol (EtOH) it becomes clearer. As an example let us consider a model sample of gasoline composed of isooctane (defines an octane rating of 100) and 10 volume % ethanol - two simple well defined molecules that for the sake of discussion mimic standard alcohol containing gasoline. Isooctane has a density of ~ 0.692 g/cc and a molecular weight of 114.23 g/mol, and ethanol has a density and molecular weight of 0.789 g/cc and 46.07 g/mol respectively. When we turn the crank on all these numbers to find out exactly how many molecules of each component there are in the gasoline/EtOH blend, it turns out that there is ~ 1 molecule of EtOH for ever 3 molecules of isooctane! That's a lot of alcohol, and far more than the average person would intuit to be present in a 90/10 blend. Thus, on a molecular level, the sample is really 25 mole % alcohol.

Transitioning back to Rogers Corp let's consider what they may or may not be doing in making their Nitrophyl materials. This author adds the disclaimer here that he has no knowledge of their business or processes, and that the following is pure conjecture on his part. Emulsion polymerizing NBR rubber is big business and done on very large scale by very large chemical concerns (Zeon, Bayer, etc) and I would seriously doubt that Rogers would make their own NBR, since they appear to manufacture value-added products rather than being a supplier of bulk raw materials. Since Rogers can buy any NBR composition they desire in the marketplace and convert it into their value-added products, why would they bother making NBR on their own? I suspect Rogers expertise lies in their ability to mill, compound, extrude, and cure various rubbers into an array of final products of various shapes and forms for their customers. It takes significant expertise and knowledge to mill and compound NBR (incorporating filler, plasticizer, vulcanisate, stabilizer, etc) and to mold and cure the rubber at high temperature. I'm sure Rogers is very good at what they do and have many trade secrets and possibly some intellectual property that protect their various compositions/processes.

Although we don't know the exact NBR composition each vendor uses for his/her float materials, hopefully the foregoing provides a bit more insight into the materials and issues affecting the solvent resistance of NBR rubbers.

If you desire more info on NBR rubber, there is no shortage of it on the net, but the following is a short fairly straight forward introduction to the subject.

http://www.iisrp.com/webpolymers/07nbr-18feb2002.pdf
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Re: Nitrile Rubber Floats

#2

Post by Mr.Big »

And what's even more amazing is I read that and actually understood it........ :shock:
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Re: Nitrile Rubber Floats

#3

Post by 58flh »

In my trade before they outlawed XYLENE,Im starting to wonder if all them vulcanized gaskets were made of the NM-KIND!?--we used XYLENE & guys would bathe in the shit at the end of the day-cause it wiped any kind of sealent odd your hands easily!--After the XYLENE crap with OSHA--I strickly used & ordered cases of mek-(methyl ethyl keytone)-if I remember correctly & it worked in clean-up of tooling overspray ,just needed a little more elbow grease to it.I bet I have stashed quite the array of different Vulcanized & non-vulcanized rubber gaskets & set-blocks in various thicknesses starting at 1/16 & up.WZ507 do you think its worth testing the stuff im sitting on & its sealing every skyscraper in NJ & NYC! & it saw heavy mek & XYLENE or ZYLOL as some spelled it!????--let me know & I can send to you or anybody that has proper testing equipment or I can just stick it in glass jars ,mark them & go with it!--The thing is what was the composition of the matieral I use that does not get affected?---Respecfully---RICHIE :?:
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Re: Nitrile Rubber Floats

#4

Post by 1951 adam »

WOW! TMI....or just call liberty cycle.
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Re: Nitrile Rubber Floats

#5

Post by 58flh »

YES ADAM I AGREE TOTALY!----RICHIE :!:
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Re: Nitrile Rubber Floats

#6

Post by WZ507 »

Richie,

As you note, the easiest way to check swellability is to place the material you want to know about in the solvent you are interested in and allow it to soak in a closed system (capped jar) for an extended period of time to see if it changes - dimensionally, stiffness wise, etc. To get a more exact assessment you would measure the dimensions before and after the swelling experiment to determine exactly how much the item swelled. The most accurate and reproducible means of assessing swellability is to weigh the item before the solvent challenge begins, immerse it in solvent for an extended period of time, remove it from the solvent, quickly wipe it dry and reweigh immediately to determine the weight of solvent in the part.
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Re: Nitrile Rubber Floats

#7

Post by Cotten »

Folks,

First to further answer Mr. Big's question from the locked discussion, molded floats on the market are subject to swelling because they use obsolete off-patent, or "aftermarket" formulae. Roger Corporation, which was H-D's OEM supplier since the 1950's, commands a huge royalty for the rights to mold the "M" material, which has only been available since June of '08, and under patent.
Thus, I machine seven varieties of floats from pre-cast boards as a labor service.

Sadly, if the producer of the Rubber Ducky had spent just one dollar from each of his 10,000 floats flooding the market, he could have covered the royalty.

On to Richie's question about soak-tests, my own sample Rubber Ducky survives in my local P4gas just fine, but the bloated example in my photo came in a customer's carb. Several fellows at Davenport, from around the country, reported them swelling. So you can only really test one fuel, and not really the float.

Obviously some brands of fuels are more digestive, and combinations may be more digestive than any one alone. And you never know what the next summer blend will be like.

And to comment upon WZ507's suggestion, even the bloated floats do not soak up and gain weight. They do gain volume. By the time their diameter reaches 3.415" (~87mm), they stick and overflow.
So far, only the V-TWIN "nitrophyl" offering becomes soft and springy.

Ironically, soaking floats causes the fuels to darken and sour, requiring it to be periodically changed: Floats ruin fuel as much as fuel ruins floats.

.....Cotten
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Re: Nitrile Rubber Floats

#8

Post by Omarine »

This is a great read, some of it over my head but if there is any interest I plan on posting a simple observation when I get around to it.

Im in Japan building my panhead and I have a set of stock orings. I will be ordering VITON soon. The reason I mention Japan is becasue there must be something different about the fuel here.

I say that because I also have a 96'' SS EVO sitting here that I cant ride becasue of absurd hurdles to get paperwork (different topic). Since that bike has now been sitting for a year, I start it periodically.

It can sit for a month, with no battery tender, in the shed and the same gas as a year ago and that bitch starts FIRST hot kick EVERY time.

When I was in FLORIDA, if it sat for 2 weeks, it was a pain to get started, presumably from the fuel, becasue i DID use a battery tender there.

So when I get around to it, I plan to soak the STOCK oring and the VITON oring in the local gas (one sample from a Marine base, the other fuel sample from out in town). More to follow
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Re: Nitrile Rubber Floats

#9

Post by HDChevroletUSA »

I trust you guys, but don't understand anything from the engineer, and don't have enough time to do the research. I bought a brass float and everyone said not to use it. I finally found a Rubber Duckie, thinking my troubles would be over, and now I read this.
I just want to know one thing: Tell me what to buy for my 60 with original Linkert?
Thanks
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Re: Nitrile Rubber Floats

#10

Post by Cotten »

HDChevroletUSA!

The Rubber Ducky is a marvelous piece of quality mass production, with only the fault of an obsolete material.

Your problem will only be avoiding the wrong gas pump, as the problem is the fuel, otherwise we might as well all be running corks.

Nonetheless, it should serve, even if only for the short term, far, far better than a brass boatanchor, which was far too heavy to begin with...

....Cotten
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Re: Nitrile Rubber Floats

#11

Post by socalrider »

HDchevroletUSA,
Get one of cottons floats. I put one in my 65 flh and improved idle, start up, and mileage immensely!
Suerte,
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Re: Nitrile Rubber Floats

#12

Post by Huck »

String trimmer $hit the bed. Went on a rampage and put sta bil in all my air cooled machines. Naptha? Does it help or am I wasting my money?
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Re: Nitrile Rubber Floats

#13

Post by Cotten »

Huck!

Bone dry would be safest on several levels of concern.

....Cotten
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Re: Nitrile Rubber Floats

#14

Post by WZ507 »

Cotten wrote:And to comment upon WZ507's suggestion, even the bloated floats do not soak up and gain weight. They do gain volume. By the time their diameter reaches 3.415" (~87mm), they stick and overflow. So far, only the V-TWIN "nitrophyl" offering becomes soft and springy.
Polymer physics says that if the float changed in volume it swelled, and if it swelled it gained weight. Although the weight gain might not be of the order of magnitude you anticipated, it nevertheless occurred. Since the float is light (2-3 g?) the weight gain may be on the order of hundredths of grams or maybe even less. One would typically use a 4 place balance to conduct such gravimetric swelling experiments.

All of the above is predicated on the assumption that the volume change is temporary and reversible, i.e., that nothing is removed from the float (dissolved out of the float during swelling) and that the float recovers to original dimensions upon dry down.

As a fun aside to all this swelling talk, might there be an extra nitrile float (not Nitrophyl M) of limited value in your possession, that could be swelled in a good solvent (acetone or toluene), to see just how big it might get? It would be neat to see a severely bloated float with a x-section about 2x that of the dry counterpart.

The picture below shows 2 identical cross-sections of air cleaner foam. The piece on the left was submersed in acetone for ~ 5 seconds and wrung out prior to taking the photograph. After ringing out, there was obviously no perceivable weight gain to the human hand, but rest assured if it swelled it gained weight.

Air Filter Foam.jpg
Air Filter Foam.jpg (444.07 KiB) Viewed 3373 times
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Re: Nitrile Rubber Floats

#15

Post by Cotten »

WZ507!

I could measure such infinitesimal weight changes if it were necessary,
QALCNTRL.jpg
QALCNTRL.jpg (63.68 KiB) Viewed 3342 times
but it is a mute point when dimension is the issue.

And no, once a float bloats, its shrinkage when dry is equally miniscule.
They stay fat. OEM "Armstrongs" have even swollen to the point of splitting, and typical ones remained bloated on my Christmas tree for years (until the puppy ate them).

Unfortunately, I do have a stock of pre-M floats, although all mis-machined Scheblers. Never did the pre-M material swell in my own tests, however I have quite a selection that have been returned to me from around the Nation for replacement. Identifying the digestive component of P4gas goes beyond simple solvents.
95%/5% Ethanol/H20, nor even Methylene Chloride paint stripper affects the obsolete formula.

(Back about '08 or so, I tested a variety of solvents upon a digested tank sealer to determine a culprit of that disaster, and unless there is illegal dumping into station tanks, we should only have to deal with one of the 150+ EPA-sanctioned additives. Testing becomes impractical.)

I cannot view the aircleaner foam pics here at the shop, but it would be an apples-to-oranges comparison anyway. Nitrophyl is a "closed-cell" foam, and the aircleaners foams are naturally "open", allowing solvents and digestives in easily.
It is a mystery to me how a closed-cell foam expands when solid Nitrile or Buna-N O-rings expand dramatically with no cells at all.

The M material has a much coarser cell grain than earlier pre-cast board.The grain of cell size varies, with the coarsed in the center of boards, and finest on the outside skin.

Rubber Duckies have the advantage of a skin all the way around it, whereas mine have the cells exposed upon all but one surface.
Yet the machined M still survives, when the molded off-patent formulae have failed.

M is presumeably the thirteenth generation of the material.
Let us hope they are working on "N".

....Cotten
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