[grampajack]

I'm trying to develop a 100% safe gun oil for the military, as some of the current cleaning systems they're using are very toxic to the soldiers. I'm looking at using different vegetable oils as a base. Safflower is very desirable because it has a very high smoke point, but it's a drying oil with a very high iodine value.

Jojoba has a very low iodine value, but it's also very expensive and the smoke point isn't nearly as high. Many military grade weapons generate a great deal of heat, especially those mounted on aircraft.

I need something that is stable at reasonable temperatures, i.e. won't change its viscosity too much from cold weather to a hot weapon. So something like coconut oil is out, at least as a primary ingredient. There are actually some gun oils made from coconut oil already on the market, but the military has rejected them because they don't perform at all in even mildly cold weather.

I can raise the smoke point by adding fatty acids, primarily oleic acid, which is cheap and non toxic. I'm hoping to find a non toxic solvent to prevent gumming at lower temps. I'm going to try ethanol, but that doesn't look too promising based on what I'm reading about the solubility of vegetable oils in ethanol.

So basically my plan is to use primarily safflower oil, followed by jojoba oil and a little coconut oil. Then add oleic acid to raise the smoke point. Oleic acid also has the benefit of removing carbon, which makes it attractive for gun oil.

So is there any way I can lower the iodine value without using any harmful chemicals? It needs to be stable and not gum up even if left on a rack for several years, regardless of temperature or humidity.

[Arkcon]

What is Iodine Value?  What is its cause?  You don't want to alter iodine value, but instead what a totally different oil.  How will you achieve this?  What is the difference between oils with lower and higher iodine values?

I asked these questions because that's what we do here.  This is a learning forum.  What can you tell us, about what you know, so we can give you the best help.

[grampajack]

What is Iodine Value?  What is its cause?  You don't want to alter iodine value, but instead what a totally different oil.  How will you achieve this?  What is the difference between oils with lower and higher iodine values?

I asked these questions because that's what we do here.  This is a learning forum.  What can you tell us, about what you know, so we can give you the best help.

The iodine value is a measure of how quickly an oil dries due to oxidation. An iodine value below 115 is considered a non drying oil, and above 115 is considered drying. Drying oils are used in paint, whereas non drying oils would be used in lubricants.

For example, safflower oil is used in white oil paint. What I need to know is if it is possible to take a drying oil and add something to it that will keep it from drying out, or at least delay the process. I would need some kind of antioxidant.

[Intanjir]

So I guess by 'drying' they mean oxidation ruining an oil's fluidity. Simply adding antioxidants will only delay oxidation.

On the other hand using saturated fatty acids will avoid oxidation. Unfortunately longer saturated fatty acids will solidify at warm temperatures.
Coconut oil makes some sense since it mostly has saturated fatty acids of medium length, though apparently they are still a bit too long for cold weather.
Shorter fatty acids will have increasingly lower melting points and increasingly larger vapor pressures(and so might actually dry, ie evaporate, if present as free fatty acids).
Evaporation should be much less of a problem with triglycerides.

So an oil consisting of triglycerides of medium-short saturated fatty acids is a good avenue to pursue if you are looking for something patently nontoxic.
Trihexanoin has melting point of -60°C and the next natural size up, trioctanoin, has a melting point of around 10°C whereas tridecanoin has a very warm melting point of around 33°C.
These melting point are for the pure chemicals. If you have mixed triglycerides then the melting point can be much lower. The point is just that fatty acids with 6-10 carbons seems ideal.

They sell such stuff in health food stores under the name MCT oil. So it isn't outrageously expensive. Basically it is coconut oil which has been fractionated to remove the larger and more lucrative lauric acid and contains triglycerides of mostly octanoic and decanoic acids. The melting point is around -4°C. This could be lowered quite a lot more if transesterified with a source of hexanoic acid.

The most salient concern I have with this strategy is that moisture will eventually break the fatty acids off of the glycerol and will then evaporate and be a little stinky. I don't know whether this would occur fast enough to matter. This hydrolytic rancidification is the primary way that butter develops off odors, but butter is an emulsion and so has tremendous exposure to water.

Microbial degradation is another potential concern. These are natural triglycerides so microbes have the machinery to break them down. However oils in isolation tend to be fairly resistant to microbes since there is no ready source of water and other nutrients besides.

These triglycerides are small enough that they will boil around the same temperatures that other oils would smoke. 230°C or so. This is probably better than smoking but you would be concerned with loss of oil over time. Compare soybean oil which has a smoke point of around 260°C and a boiling point of maybe 300°C.

[grampajack]

Thanks, that's exactly the kind of info I'm looking for. Sounds like trihexanoin is exactly what I need. A melting point anywhere near -40 F would be fantastic. So essentially what you're suggesting is to start out with fractionated coconut oil, then add hexanoic acid to it?

[Intanjir]

You could do that, but you need to add the hexanoic acid chemically. You can't just mix in the free fatty acid. Besides it would smell horrendous.
Basically you would need to replace some of the fatty acids which are combined into triglycerides in MCT oil with hexanoic acid.
This could be done much the same as an esterification, but just using an ester instead of an alcohol. Ideally you would also throw in some glycerol to account for the overall excess fatty acid.
hhttps://en.wikipedia.org/wiki/Ester#Preparation

Alternatively you could just start with the hexanoic acid already attached to glycerol, so trihexanoin for example. Then you could simply mix. If you wanted to get fancy you would interesterify the two triglyceride sources. This shuffles around the fatty acids between the molecules. So if you weren't trying to add too much hexanoic then each triglyceride molecule would generally have one hexanoic acid at most. This is very useful because you wouldn't have to be worried that some trihexanoin fraction would just evaporate off early.
https://en.wikipedia.org/wiki/Interesterified_fat
This is actually almost the same thing as the above esterification.

Pure hexanoic acid or trihexanoin would probably be somewhat expensive. It would be better to find a source oil that contained a fair bit of it and not too much of fatty acids you don't want. Unfortunately I think that nature doesn't like making such short fatty acids in large quantities.

Anyways if it were me and I didn't want to learn the practical ins and outs of esterification then I would try out simply mixing trihexanoin with MCT oil and seeing if the properties were roughly where they needed to be. I would expect some issue with excessive evaporation of the trihexanoin. So long that it wasn't totally horrible I would then consider hiring a chemist in some capacity to see if transesterification or something else could be done to sufficiently improve retention over time under heat.

I wonder... what if you switched to bigger molecules by replacing glycerol with a polyalcohol which could hold more than 3 fatty acids. Olestra comes to mind. Would you be able to get substantially higher temperatures? It would probably just smoke.

[grampajack]

The only thing I could find for sale is Glycerol Trihexanoate, and it's $65 per ML? I hope that stands for metric liter and not milliliter! I don't even know how they could package 1 milliliter, or what you would even do with it, so I'm assuming that means liter.

If it's per liter, then that might be doable depending on how much was needed. So you're saying to blend this stuff with fractionated coconut oil and just mix it with a spoon? No chemistry involved?

How much do you think would be needed?

*MOD Edit - remove monster quote*

[Arkcon]

The iodine value is a measure of how quickly an oil dries due to oxidation. An iodine value below 115 is considered a non drying oil, and above 115 is considered drying. Drying oils are used in paint, whereas non drying oils would be used in lubricants

Not exactly what I was looking for here.  The iodine value is a test of the level of unsaturation in an oil.  For example: the USP test for olive oil specifies:

Iodine value <401>: between 79 and 88.

Out side of that range, one would expect that the olive oil is mixed with another oil, or possibly highly degraded.  Its true that the drying oils, for example, linseed oil are very highly unsaturated, and that allows linseed oil to polymerize into a varnish or with the addition of fillers, be made into linoleum.  But what significance those facts have, on the usefulness of a particular vegetable oil, as a gun oil.  Or how affecting iodine value, or blending vegetable oils of varying unsaturation levels, or smoke point is explained by the many walls of text above, I can't fathom.

OK, lets try this.  Gun oil is typically white lithium grease -- a soap made of the reaction between  lithium salts and various fatty acids, dispersed in hydrocarbon oil.  Simple, no corrosive, doesn't spoil.  What's wrong with it?  Why is it used anyway?  And what are you doing to replicate its properties in vegetable oils?  And blending oils with antioxidants is not the answer to the last question.

[Intanjir]

Yikes, that is steep. They mean mL, lol. I would call/email around and see if someone can direct you toward a less purified source. Also I would compare prices for hexanoic acid since you can make it from that with just cheap glycerol. If the free acid is much cheaper then go ahead and get that and be prepared to read up on esterifications, lol.


Yeah, you should be able to just mix in the trihexanoate and be within a ballpark of how it would behave if you instead transesterified it with the MCT oil. At least for most parameters. We would expect the evaporation at high temperatures to be quite a bit higher when just mixing.

I have no idea how much you would need. It depends on what physical parameters you want to measure and how you go about measuring them. At a minimum you'd want to find the melting point of the various samples you mix as well as measure viscosity at relevant temperatures. I don't claim to know much of anything about lubricants and their figures of merit. You'd also want to verify that it is compatible with whatever additives are needed besides just the carrier oil, ie grease and boundary lubricants or whatever.
Anyways, the main concern I would have is whether the final lubricant is sufficiently resistant to moisture over time. Fatty acids are more polar the shorter they are, so water might be able to gain a foothold.

You might just try playing around with turning just the MCT oil into a proper lubricant as a first project. Even though low temperature performance might not be ideal you will still get an understanding of what all needs to come together.

[grampajack]

Lithium grease hasn't been used on small arms since the M14 was taken out of service in the sixties. They still use some old M14s as DMRs, but those are slowly being replaced and I don't know what kind of lubes they use on them nowadays. Likely some kind of synthetic. Largely, lithium grease has been replaced by TW25B, which is a synthetic oil thickened with PTFE.

I think you're missing the point, though. I'm not trying to improve upon the performance of current gun lubes, but make a completely non toxic one that meets the performance of currently used synthetic lubes. There are non toxic lubes already on the market, but they perform terribly at low temperatures and have a higher burnoff rate than synthetics. To be useful to the military, it has to perform at temps as low as -40 F.

And when I say completely non toxic, I mean something that you could eat. It's a like a doctor said one time, don't put anything on your skin you wouldn't want to eat. And considering that many of the base oils used in lubricants are carrier oils, you're going to see very high absorption of any additives. So even relatively minor toxins could be amplified by the carrier oil when they get on skin, and you could see much higher absorption than expected.

*MOD EDIT -- remove useless quote*

[Arkcon]

OK.  How are you achieving your goals with the additive suggested?

[grampajack]

OK.  How are you achieving your goals with the additive suggested?

I really don't understand what you're after. I'm the one looking for help, not the expert. If you're referring to the trihexanoate, the goal is to make the base oil more suitable to colder temperatures. That's the area where current attempts have failed.

Like I said, I really don't know what you're wanting from me.

[grampajack]

Okay, I found hexanoic acid as cheap as 30 dollars for 4 ounces. I'm sure I could order it in bulk from Alibaba cheaper than that. So how complicated would it be to combine it chemically with fractionated coconut oil? And how much would it take, ballpark? Are we talking less than 10% hexanoic acid? If the final product was more than about 10% hexanoic acid, then it might be too expensive to be viable. The military wouldn't consider anything that was more expensive than the status quo, no matter how good it was.

[Intanjir]

You suggested -40°F as a performance target. Curiously this happens to be the temperature that Fahrenheit and Celsius are equal: -40°F=-40°C. Anyways, this is fairly low. Trihexanoin melts at -60°C and MCT melts around -4°C. You would need a fair bit of it, but there isn't an easy way to come up with a good estimate. In any case you might want to aim for the vicinity of a eutectic.

A potential commercial source of hexanoic(capric) would be some varieties of cuphea:
https://en.wikipedia.org/wiki/Cuphea_oil

I don't know the practicalities of interesterifying/esterifying. I think one way to do it goes something along the lines of mixing your reagents with a small amount of sodium methoxide and applying heat. This might not work well if there is too much free fatty acid as each fatty acid molecule will release a water which might interfere with the methoxide catalyst. You should look around in the literature for specific procedures.

[Intanjir]

Ahh, I was mistaken with cuphea. I confused capric with caproic. Though, in all fairness, about 90% of the blame goes to the poor imaginations of goat-obsessed Victorian chemists.