Pretty much anything not covered by the topics above. Short lived production bikes or vehicles, Electrical, Tires, Paint, Brakes, etc. Use this for tech questions, and "Shoot the Bull" for general conversation, no tech.
Gasgacinch (one of my favorite goobers) is bright yellow and stays rubbery, whereas this stuff is very dark red to black where aged inside the tank, and quite hard until I hit it with acetone.
That doesn't mean that there may not be a base chemical similarity, or that a decade of fuel stains may not have changed it as well.
But fresh Gasgacinch didn't do this well in P4gas! (Nor the very similar 3M Weatherstrip Adhesive.)
The felt adhesive would have to date back to the WW2 era, and probably less exotic of a material than we might imagine.
As I posted, all of these similar goobers may well have the same base.
( I have some Permatex Aircraft goo left over from the '60's....still in the same family. It doesn't harden.)
It was my hope that someone may have knowledge of the Factory's preferred slop.
(And slop it they did, with a big brush or swab.)
Forgive me for looking backwards, but relying upon modern brands, even as noble as Gasgacinch, might blind us to the obvious when it comes down to compounds that our fathers took for granted.
Too much knowledge is being lost, and apparently the original felt adhesive is one of them.
Let us all keep an eye out for clues....
I don’t want to head off too deep into the land of polymer science here, but a few comments are in order to help us appreciate the difference between a cured/crosslinked polymer and an uncrosslinked polymer. Let’s take a familiar example - Amazing Goop adhesive. This is a linear thermoplastic polyurethane solution that is delivered as a viscous solvent solution (toluene). Upon dry down a tough urethane elastomer/adhesive results. However, this resulting tough adhesive is not cured, and can be readily dissolved by re-exposing it to a “good” solvent (the one it was delivered from, or many others). As it dissolves it will swell and go back into solution resulting in the formation of a viscous solution.
Now let’s consider a curable adhesive example - Gorilla Glue, which has no solvent and is 100% adhesive. This too is a polyurethane, but this is a curable, or crosslinkable, polyurethane, i.e., it has reactive sites that cause the polymer to crosslink (x-link) upon exposure to atmospheric moisture. Once cured, the resulting rigid adhesive can not be re-dissolved, i.e., it may swell with a “good” solvent, but will never dissolve, and the solvent used for swelling will show no increase in viscosity, because no polymer is dissolving. The take home lesson here is that another means of reducing a coating’s susceptibility to solvent swelling is to x-link it.
Back to the issue at hand - vintage tank sealers and their removal. Tank coatings in general protect the tank by being impervious to motor fuels (non-polar solvents such as alkanes and toluene), and some of our trouble in recent times with tank sealers occur as the polar content of the motor fuel increases due to addition of ethers and alcohols. That said, tank coatings have historically been formulated primarily to be incompatible with non-polar solvents, but unfortunately, this was achieved by making the coatings themselves more polar. As our motor fuels trend to higher and higher polar content the old coatings are not always up to it, and become susceptible to swelling in the modern fuels.
The fact that Cotton’s tank coating can not be dissolved may suggest that the factory used a reactive coating that x-linked upon application, in which case it will not dissolve but would be swellable with a good (polar) solvent. According to Cotton’s earlier comments, the subject coating is swelling and becoming gelatinous, but not dissolving, as evidenced by no color (or solution viscosity?) in the solvent. This is classical behavior of a x-linked coating, where the polymer swells, but does not alter the solvent viscosity. However, it’s also possible that acetone may not be the best solvent for this coating. Sometimes the polymeric coating can be a block copolymer, and the solvent you choose will swell one block and not the other. This would also result in swelling, but no dissolving the coating.
Perhaps the best thing you can do at this juncture if you are still curious about dissolving the subject coating is to take the chips you have removed, and try systematically working through a range of solvent polarity to see if you can identify a suitable solvent. For such experimentation you want a relatively polar and a non-polar solvent pair. For the polar solvent you cold use acetone or an even more polar solvent would be isopropyl alcohol (be sure you are not using rubbing alcohol which is 70% isopropyl alcohol 30% water). As the non-polar component you could try toluene or mineral spirits. If I was doing it I would start with acetone and toluene. Make up solutions containing 0, 25, 50, 75, and 100% toluene in acetone, put chips into each, and seal. Let them stand, or better yet agitate them continuously, for days, then inspect to see what they look like (color leaching?, any viscosity change?, etc) and what they feel like (minor softening of the chip, major softening of the chip, etc), and it should become readily apparent whether the polar or non-polar end of your experimentation is getting you anywhere. Continue experimenting over narrower ranges of solvent proportion if you see something promising. In the end, if you have no success dissolving the coating with any solvent blend you may have to declare it a crosslinked coating. Someone’s earlier advice to use paint remover (for a prolonged period of time in the tank) was also good counsel, as this would stand a very good chance of swelling the coating.
One final note on tank coatings. POR 15 is a curable polyurethane that once well cured should be impervious to common fuels (and no I have nothing to do with POR 15, I don’t care what you seal your tank with, but I do like things to make sense, and POR 15 swelling in motor fuel doesn’t make sense to me). In the above instance where Cotton found it to be otherwise, I suspect that for whatever reason it did not cure adequately. Again, if you have any doubts about a coating’s integrity in a given fuel, create a well cured sample of the coating (to obtain test chips) and expose it to the fuel of interest to see how it fairs. I realize this shouldn’t be on us to figure out, but when things don’t work the way we expect our only resource is more experimentation.
I seem to follow your description somehow, as an isocyanate urethane that I use pulls moisture (or something) out of the air to dry quickly, and up to 30 days to completely cure (cross-link), and then resist common carb cleaners and P4gas.
The "Pink Goo" reference dates back a season or three when a local's seasoned red tank liner suddenly morphed into the blob.
That material also de-gelled when dried, to its own degree, and I then placed squares of it into baby jars of various solvents, from acetone to xylol, with punctilious ethanol in between.
Some solvents took six months to digest what P4gas could do in week. The ethanol didn't touch it.
To generalize my conclusions at that time, it is either detergents and injection cleaner additives in USA pump fuels that digest our soft parts, perhaps augmented by the ethanol (or it is rectification residuals left in the ethanol to denature it, and avoid sin tax).
On to POR 15, my studies in summer-blend Shell Premium suggested that the "15' stood for "15 minutes"
I lost a couple of $Gs when it obviously never cross-linked.
Thanks for posting this info..Very interesting read...I'm saving this article...
And until I personally experience a problem with Por15, I'm gonna stick with it..
It has been & is still working good in my Flathead Servi tank.
Although I did let it cure about a month, while being pre-occupied with other work on that trike..
Cotton - “isocyanate” is the functional group on the polyurethane prepolymer that causes it to cure when exposed to atmospheric moisture (even in the driest of ambient conditions there is enough moisture in air to cause this reaction to occur, but it certainly occurs faster in high humidity air). This is the universal cure mechanism for all one-part PU compositions (Gorilla Glue, AquaSeal, POR 15, etc). You sound like a good experimenter since you have previously conducted your own solubility studies, sweeping a range of solvent polarity to assess solubility. In the example you cite above, the anhydrous (dry, 200 proof) ethanol would be far more polar than acetone, thus too polar to touch the pink goo and the reason it didn’t work. A small amount of ethanol (5%?) in toluene (toluol) or xylene (xylol) might possibly work.
One final comment about solvents and the solvating capability of solvent blends. Most people have the common misconception that when you blend two solvents you have the benefit of both individual solvent properties in the final blend, e.g., if acetone is good for dissolving some polar coating (functions like a paint stripper) and mineral spirits is good for dissolving some heavy oil residue, a blend of the 2 solvents will be good for both dissolving coatings and cleaning up heavy oil residue. Unfortunately, this is not true.
By blending 2 solvents, you have created a new solvent that has neither the property of solvent 1 nor solvent 2, but rather has properties intermittent the 2 starting solvents. For example consider acetone and mineral spirits (MS) as a solvent pair. Acetone is a relatively polar aggressive solvent that may swell/dissolve rubbers, paints, coatings, etc. In contrast mineral spirits (alkane mixture - akin chemically to isooctane but much higher boiling) is a very non-polar solvent that may swell some rubbers and dissolve oil and grease, but aside from these features is a weak solvent that is generally safe to use on almost any paint or coating without fear of swelling/damage. Now consider an 80/20 acetone/MS blend. Do you have the aggressive nature of the pure acetone in this blend? No, because you no longer have pure acetone and have lowered the solubility parameter and the polarity, thus decreasing the aggressive nature of the solvent by introducing MS. Now consider the opposite case, a 20/80 acetone/MS blend. Do you have the aggressive nature of acetone? Again, no, this blend is a new solvent that is even less aggressive than the previous blend and much more like mineral spirit than acetone, yet slightly more aggressive than pure mineral spirits.
The foregoing hopefully illustrates why one might employ solvent blends, rather than pure solvents, to solvate specific polymers or provide specific solvent properties. It can sometimes be quite a fine line between solvents that provide the desired action and those that don’t, and blending affords you a means of probing the intermediate region between the pure solvents. Hope this is clarifying rather than confusing.
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