Sciencemadness Discussion Board - Factice rubber-based propellants from vegetable oils

Factice rubber-based propellants from vegetable oils

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deltaH - 14-3-2015 at 11:31

'Factice' rubber is the material obtained from vulcanising polyunsaturated vegetable oils. This means reacting things like linseed oil with sulphur.

I was wondering whether this might not be a good candidate to marrying with sodium/potassium nitrate for a propellant... think black powder, but with the sulphur and fuel component combined... a better fuel than charcoal to boot, plus potentially castable.

Reference:

http://naldc.nal.usda.gov/download/24579/PDF

[Edited on 15-3-2015 by deltaH]

kecskesajt - 14-3-2015 at 22:29

I tryed to make hard margarine + KNO3 rocket fuel but it wont work.Even when I cooked out the water.It just dont want to burn.Isnt vulcanisation for hydrocarbons only?Like the tire on my bike or car.

deltaH - 15-3-2015 at 01:01

Quote: Originally posted by kecskesajt

I tryed to make hard margarine + KNO3 rocket fuel but it wont work.Even when I cooked out the water.It just dont want to burn.Isnt vulcanisation for hydrocarbons only?Like the tire on my bike or car.

Fats and oils by themselves won't burn well with an oxidiser like KNO3 because they would just melt and boil before hitting the temperature KNO3 can oxidise them. A heavy rubber, on the other hand, can burn because it is so heavily cross-linked that it doesn't melt, instead it chars and decomposes.

Vulcanisation occurs when short sulfur chains cross-link unsaturated hydrocarbons. With vegetable oils, the linkage occurs at sites with double bonds, particularly at the -CH=CH-CH2-CH=CH- carbon which is more reactive. Vegetable oils that have a very high degree of unsaturation (double bonds) also work and the resulting brown rubber is called 'factice'. Oils with the highest degree of polyunsaturates probably work the best. These are called 'drying oils'. A good example is linseed oil and is also readily available from the hardware stores and very cheap.

One would have to re-work the normal black powder formula for the new stoichiometry of course. A guideline could be to use enough sulfur to convert all the KNO3 to K2S and enough KNO3 should be used so that the oil can be fully oxidised to CO2 and H2O when burned, for example.

To make a factice rubber, the vegetable oil, for example linseed oil, would need to be first cooked with the sulfur at above it's melting point for some time until it begins to thicken. This would probably stink and fume terribly!

Hypothetically speaking, this could then be mixed with the KNO3 and cast into a mold, air bubbles removed and then baked further until fully hardened. There is a fair chance that this could self-ignite in the process, a greater danger for larger castings I would imagine, so all the necessary precautions assuming this would happen would need to be taken, of course.

The would all be very dangerous and should only be attempted by experienced professionals who can safely carry it out and are legally allowed to do so.

[Edited on 15-3-2015 by deltaH]

Fulmen - 15-3-2015 at 03:38

Interesting. I've played with rape seed oil and sulfur before, but never seen it crosslink to a solid. I use it as a cutting oil, 5-10% sulfur produces an excellent EP-lubricant for metal cutting. At low temperatures the sulfur appears to simply dissolve, in one test it simply precipitated out again when cooled. With higher temperatures and longer holding times it seems to react completely. Some residual dissolved sulfur is to be expected I think, but as both dissolved and reacted sulfur are said to have EP-properties I never studied it any further. I got my cutting oil and was happy with the result.

An inert blanking sounds like a sensible advice, my experiments produced something that smelled like a dead sheep marinated in used engine oil. Some H2S must be expected, probably not enough to make it dangerous but it does smell funky when fresh.

As for stoichiometry an over-fueled mix would be the best, look at Nakka's work on KNO3/sugars. Not only should one strive for low MW exhaust products, reducing the amount of solids also improves nozzle efficiency. For KN/SU the stoichiometric ratio is appr 75% KNO3 while the best performance is found at around 65% IIRC.

deltaH - 15-3-2015 at 04:12

Thanks Fulmen. Yes, most commercial factice seems to be made with low-cost oils like rapeseed and the like but I think one could target something harder by using a highly polyunsaturared oil like linseed oil, which is a 'drying' oil.

I've also dissolved sulfur in sunflower oil by strong heating which went brown and smelled horrible, but like you, I didn't see gelling, but commercial brown factice rubbers are solids, so it can be done. I think they need to be baked for long periods of time to fully cross-link, but I suspect it won't be more than a few hours with linseed oil. Temperature, of course, changes everything

At my hardware store, there's two kinds of linseed oil sold, one is 'ordinary' linseed oil, the other is boiled linseed oil. Supposedly, the latter is partially oligomerised already by strong heating, which would be a good thing, but I've read on somewhere that often this is ordinary linseed oil with a metal accelerant (catalyst) added, which could be a very bad thing or a good thing, who knows

Interesting what you said about the oxygen balance, I was thinking this might be the case but didn't have specifics to advise as you have. Thank you very much for sharing that. It would definitely help in terms of the physical properties of the propellant to have more factice in the composition.

Here's a picture of solid brown factice gotten from http://www.tradeindia.com/fp1157451/Brown-Factice.html because I know that people are going to moan that they're not getting theirs to solidify

[Edited on 15-3-2015 by deltaH]

Fulmen - 15-3-2015 at 04:58

As far as linseed oil goes IIRC there are two types: raw and "boiled". Even the raw should polymerize given enough time and oxygen, but it is quite slow. Heating/boiling it speeds up the process giving a partially polymerized oil that cure much faster, today siccatives are used to catalyze the process.
For factices I'm unsure if there will be any difference between raw and boiled, but as there are two different bond types I'd start with the raw oil just to be sure. The siccatives could possibly accelerate the reaction to the point where runaway reactions become an issue.

According to this document rape seed and similar oil will give a hardness of 30 shore A, this is comparable to a rubber band. Not sure if there is any way to increase this other than using something like linseed, perhaps one could dissolve other polymers? I believe I have some sulfur somewhere, I think this is worth a bit of research. A curable composite propellant using household chemicals is pretty much the holy grail of amateur rocketry.

deltaH - 15-3-2015 at 05:20

"The siccatives could possibly accelerate the reaction to the point where runaway reactions become an issue. "

Yes, my worry as well.

"A curable composite propellant using household chemicals is pretty much the holy grail of amateur rocketry. "

In my country, KNO3 is available from commercial fertiliser companies that sell 25kg bags of it for something like $20-30 if I remember correctly. I recall seeing multi-kilo bags of "flowers of sulfur" available cheaply from the larger nurseries. So yeah... this could be a REALLY low cost way to build rocket motors if it can be made to work properly and if it doesn't spontaneously ignite during baking :mad:

Fulmen - 15-3-2015 at 05:57

This PDF looks relevant: www.ijarnp.org/index.php/ijarnp/article/download/212/pdf_6

deltaH - 15-3-2015 at 06:38

Some more literature... discusses some activators and accelerators useful for making factice.

Attachment: Rubber seed factice.pdf (323kB)
This file has been downloaded 845 times

Also found this tidbit:

From:

https://books.google.co.za/books?id=2CYDAAAAMBAJ&pg=PA24...

So at least we know factice can also be made from linseed oil.

[Edited on 15-3-2015 by deltaH]

Linseed factice.JPG - 26kB

Ah ok, here's an in-depth article about linseed oil factice.

Attachment: Linseed factice article.pdf (378kB)
This file has been downloaded 547 times

Looks like adding magnesium oxide results in a much harder linseed factice and faster cure, interesting!

I suspect that it might be due to the formation of magnesium soaps from the oils and then cross-linking them... double wammy!

[Edited on 15-3-2015 by deltaH]

Fulmen - 15-3-2015 at 07:30

Very nice find, an IRHD (should be roughly equal to Shore A) of 70 sounds promising. I see great potential in this, and considering that the KNO3/sucrose-propellants have an auto-ignition point above 300°C the odds of this fuel igniting should be low. This must be tested of course, but I see no reason not to test it.

deltaH - 15-3-2015 at 07:35

I think the autoignition could be a problem for large diameter castings. The paper does state that the reactions are exothermic, so there will exist some diameter of motor where the centre will heat up more than it can lose heat to the casing and so run away. If the casing is made of paper, then there is an added insulator.

Working from the magnesium oxide forms magnesium soap hypothesis, I calculated the stoichiometric amount required for linseed oil from its saponification number.

The result is 69g MgO/kg linseed oil. I guess it should be as fine a powder as possible.

[Edited on 15-3-2015 by deltaH]

Fulmen - 15-3-2015 at 08:04

True, at some point it will pose a problem. There are however the possibility that it could be partially polymerized, cooled, mixed with oxidizer and reheated to a lower temperature for a controlled curing. If you look at page 62 in "MANUFACTURE OF DARK FACTICE FROM RUBBER SEED OIL" it shows the reaction temperature over time, it looks like the bulk of the heat is evolved before gelling.
Another possibility would be to mix pre-cured and uncured propellant. But all in all I don't think this will be an issue for small scale testing.

[Edited on 15-3-15 by Fulmen]

deltaH - 15-3-2015 at 08:11

Yes exactly, also what I suggested earlier, first react the sulphur and oil until you get the sulfur dissolved and to thicken/gel the oil, then mix in the KNO3 powder, cast and bake to cure. I'd also add the MgO powder with the oxidant so as not to over thicken the initial phase. One still needs to be able to get out the air bubbles from the casting before curing.

I'm very excited about this, I wish you luck with the experimentations. Sadly, I now live in an apartment and can't experiment with this :mad:

[Edited on 15-3-2015 by deltaH]

Fulmen - 15-3-2015 at 09:32

So do I, hasn't stopped me so far. I like the idea of mixing the MgO into the oxidizer, another is to add the sulfur incrementally. There must be a minimum amount needed to cause gelling, so by keeping below this it should be possible to reduce the heat during final mixing.
In fact I am fairly confident that this can be done safely even for large grains, the real question is whether the mechanical and chemical properties are suitable.

PHILOU Zrealone - 15-3-2015 at 11:17

Ultrasonic bath or probe (like smog generator/ultrasonic humidificator) will help to drive the air bubbles out of the mix.

[Edited on 15-3-2015 by PHILOU Zrealone]

deltaH - 15-3-2015 at 11:31

Bert's signature quote seems REALLY appropriate right about now...

Quote:

Boom.
The explosion removed the windows, the door and most of the chimney.
It was the sort of thing you expected in the Street of alchemists. The neighbors preferred explosions, which were at least identifiable and soon over. They were better than the smells, which crept up on you.
-Terry Pratchett, "Moving Pictures"

[Edited on 15-3-2015 by deltaH]

Fulmen - 15-3-2015 at 11:49

I did a quick test with some rape seed oil and sulfur in a small test tube. I've heated it repeatedly with a torch before allowing it to cool. First run only dissolved the sulfur which precipitated back out again upon cooling, next run gave a dark oil while the third gave a slightly sticky, crumbly rubbery solid. Sadly it doesn't seem to be strong enough to work as a binder, but according to the literature linseed oil could work better so I'll try that next. It also melts upon heating, but that might not matter much. After all melted sugars do the same yet they work fine in propellants.
Another issue is the smell, there is a lingering sulfurous odor that is less than agreeable in the long run.

deltaH - 15-3-2015 at 12:04

...and we're off. Well, that's not a bad start for factice-making. The weakness isn't a concern too much as I suspect MgO would stiffen it considerably. Yes, the odours are really terrible, but the saponification helps here a bit. When I made the sunflower wannabe factice (which didn't solidify), I was stuck with a rather large amount of dark brown absolutely horrid oil. My solution was to saponify with NaOH. The resulting hard soap smelled considerably less (though still horrid). I also experimented with trying to saponify with calcium hydroxide and moderately strong heating (minus sulfur), but struggled to get it to set.

Fulmen, please take pictures if you can!

[Edited on 15-3-2015 by deltaH]

Fulmen - 15-3-2015 at 13:42

If I find something interesting I'll try to document, but right now I'm just throwing science at the wall to see what sticks. I have no idea what to expect, so why not just muck about a bit and see what happens...

I've started looking at the world of drying oil, and there are a lot of variables to play with from raw oils to "blown" or "stand oil" to catalysts. And then there's the oils themselves, properties seem to wary significantly.

White factices made with S2Cl2 are said to be the main constituents of rubber erasers, if so it could work as an example of probable properties. And I wonder if it's low resistance to abrasion would cause problems.
But if we can end up with something closer to thoroughly polymerized linseed I thing we're onto something.

[Edited on 15-3-15 by Fulmen]

PHILOU Zrealone - 15-3-2015 at 15:14

The smell comes from H2S and thiols R-SH generation above a certain temperature...this is common to hydrocarbons heated with sulfur!
The smell will be diminished somehow if you have a H2S or thiol scavenger.
Mineral bases are a typical example...
NaOH + H2S --> NaSH + H2O
2 NaOH + H2S --> Na2S + 2 H2O
R-SH + NaOH --> R-SNa + H2O

Some heavy metals or cations may help precipitating the odorless sulfide... (Hg, Ag, ...)

deltaH - 15-3-2015 at 22:07

Yes and I suspect the culprit is the glyceride component of fats which at high temperature can form all kinds of volatile and 'yummy' sulfur compounds. Oh well, no pain... no gain

Organosulfur chemistry is nearly always going to be a stinker.

There are indeed a lot of things to explore with these formulations. Chemical inertness permitting, burn catalysts like freshly precipitated ferric hydroxide/goethite could be helpful.

Incorporation of aluminium or magnesium powder opens up another can of worms. Lots and lots of things to consider. Heck, I wonder if you could even make am oxidant free propellant by using high sulfur in the oil and aluminium, i.e. linseed, sulfur and aluminium powder only, using enough aluminium to form Al4C3, Al2S3 solids and H2

Fulmen - 16-3-2015 at 00:23

I've been digging through the literature in the hopes of finding something on odor control, but haven't had any luck yet. The stuff I just made is a stinky mess, hopefully there is a way to reduce the problem. Using strong bases wouldn't be my first choice as it might be incompatible with the propellant, nor do I see dangerous heavy metals as a good solution. Luckily most metal sulfides are insoluble so finding a safe candidate shouldn't be that hard.

deltaH - 16-3-2015 at 00:34

One idea for odour control is mixing MgO and linseed and cooking until it's fully saponified, then make flakes and wash the solid to remove glycerine (I doubt Mg soaps are soluble) and other low molecular weight impurities.

The resulting waxy solid can then be mixed with sulfur and KNO3, pressed into the mold and then baked at 180C to vulcanise.

[Edited on 16-3-2015 by deltaH]

PHILOU Zrealone - 16-3-2015 at 04:46

Quote: Originally posted by Fulmen

I've been digging through the literature in the hopes of finding something on odor control, but haven't had any luck yet. The stuff I just made is a stinky mess, hopefully there is a way to reduce the problem. Using strong bases wouldn't be my first choice as it might be incompatible with the propellant, nor do I see dangerous heavy metals as a good solution. Luckily most metal sulfides are insoluble so finding a safe candidate shouldn't be that hard.

Not that hard?
It has to be:
-a basic oxyd or hydroxyd...solubility would help a lot to catch faster the H2S ... but MxOy or M(OH)z are usually unsoluble.
-a soluble salt but the counter anionic part will thus deliver an acid...
MxZz + H2S --> MxSz + HZ

deltaH - 16-3-2015 at 05:38

One has to be careful with the use of sulfur scavengers lest it reverses the vulcanisation

Bert - 16-3-2015 at 06:29

MSDS for the brand of "boiled" linseed oil sitting in my painting supplies-

http://www.sunnysidecorp.com/pdf/msds42.pdf

Various Cobalt and Manganese compounds are used to catalyze the polymerization, rather than the old fashioned Lead compounds.

As far as de gassing composite fuels before solidification, that may be done with a vacuum chamber and vibration for those formulations which are fairly liquid and pourable . For mixtures that can be handled like a cookie dough, it is common for amateurs to just consolidate them into motor case or a surface bonded grain "sleeve" without vacuum or other de gassing techniques. This is popular for smaller motors and less well equipped amateurs-

deltaH - 16-3-2015 at 08:30

Cobalt and manganese compounds would make great burn catalysts to, if they don't cause ignition prematurely during baking.

I'm excited to hear how linseed vulcanisation went. Particularly interested in the MgO 'trick', though I suspect it's not going to be easy to get it to react. I have a 25kg bag of industrial MgO product (mineral origin). It cost just about nothing, but it's very crude and impure and in the form of burnt flakes, a bit like burnt lime flakes. I suspect one would need to pulverise this really fine for it to work if my experience with lime saponification is anything to go on. Then again, 180°C is pretty hot...

To be honest, what I like about this idea (very much) is the low cost and simplicity... which in my opinion is worth having to deal with the smell, especially if the final set product is not going to be so bad. My factice soap bar I made only smells unpleasant when you stick you nose to it.

So honestly, I don't think it's worth the effort to remove glycerine as I've suggested before. Just need a fume cupboard for the initial stages or work outdoors far from people and stand upwind

You need to setup an oven outdoors to bake it during the cure stage... one that you can afford to lose and also never use again for anything else.

Damn, I really wish I lived somewhere remote and owned a small piece of land... donations welcome of course, all in the name of science

[Edited on 16-3-2015 by deltaH]

Fulmen - 16-3-2015 at 08:56

No significant progress yet, I've spent the afternoon synthesizing MgO. While others might disagree I feel that the smell from a direct vulcanization is a deal-breaker. Maybe it can work, but I'm not going down that road.
I'll admit that my test was crude, so a more careful setup might mitigate the problem. I'd really like to know how they handle this commercially, but haven't found anything yet. Nitrogen-flushing is mentioned in the first PDF, but as it is pretty much out of the question for our target marked we'll have to come up with an alternative.

For now I'm going to explore what MgO can do, but it'll take a couple of days to get a finished product.

deltaH - 16-3-2015 at 10:11

I'm glad you're making the MgO, because I think it's going to be key.

Fulmen - 16-3-2015 at 10:36

That seems to take it's sweet time. All I could find was some Mg-chips from a band-saw, most likely a mix of pure and alloyed containing ~5% Al and a tad of Zn. After digesting it in HCl I precipitated it as Mg(OH)2 using NaOH, but this precipitate will not settle out. I'll have to wash/decant it before drying, so it looks like I need a flocculant.

deltaH - 16-3-2015 at 10:48

I don't think "milk of magnesia" will settle out on its own

You can buy flocculant from the pool section of the supermarket or pool supplier, it's sold as "pool clarifier", in my country. Check composition.
Polymeric anions might work too... e.g. antacid that is based on sodium alginate, e.g. Gaviscon
Also xanthan gum, it's available in some health food retailers here.

Do dilute the flocculant heavily before using it.

I'm happy you're preparing magnesium hydroxide as this is likely the most active form. I don't think bulk MgO would be nearly as reactive.

[Edited on 16-3-2015 by deltaH]

Microtek - 17-3-2015 at 02:05

You could also try igniting the Mg turnings and collecting the ash (MgO)...

Fulmen - 17-3-2015 at 02:23

I tried starch, and while it did seem to help it didn't exactly cause it to settle out. But it thickened enough for filtering through cloth. I'm only making ~25g, so it's not too much work if one have a bit of patience.

j_sum1 - 17-3-2015 at 02:59

Quote: Originally posted by Microtek

You could also try igniting the Mg turnings and collecting the ash (MgO)...

Ummm. That's what I would do.

Praxichys - 17-3-2015 at 08:22

-- Speculation Alert --

It seems to me that there are some points to be gathered from this:

1. Degree of polymerization, and thus stiffness, is likely controlled by the number of unsaturated bonds in the starting oil.

2. Triglycerides in the starting product may yield glycerol if any strongly acid or base conditions exist. (MgO, H2S) which might lead to a runny, stinky liquid. (Insert poop joke here)

The following is a table of various oils with their percentage of unsaturated bonds, from Wikipedia:

I think a good approach (albeit a few more steps) is to:

1. Choose an oil which gives an appropriate degree of cross-linking when vulcanized
2. Saponify the oil with hydroxide and separate the soap from the glycerin
3. Acidify the soap to recover the unsaturated fatty acids
4. Form ammonia salts with the fatty acids, which dehydrate to amides on gentle heating
5. Add well-mixed oxidizer and sulfur blend to molten amides, cast, and bake to vulcanize.

In theory, the amides will scavenge H2S. The oil industry uses this to desulfurize petroleum. The amides also add nitrogen and hydrogen, which is a good thing for a propellant. (High delta-Hf for N2, low MW for H2)

Or, use transesterification instead of saponification to make maybe methyl esters of fatty acids, a la biodiesel. Separate the glycerol, add the oxidizer and sulfur to the oily part, and bake to vulcanize. In theory, the ester falls apart in heat plus H2S acid, and the alcohol flies away on the wind, which might help with hardening.

If runaway thermal events happen during vulcanization, there is a way around it. Simply pre-vulcanize an amount of propellant in a pan, then shred it into chunks and mix that with a fresh batch. The pre-vulc stuff reduces the heat generated per unit mass and would probably be effective at stopping a runaway. This is much like using grog (crushed and fired refractory) to prevent excessive shrinkage in uncured refractory mixes.

In any case, I would advise against leaving the glycerol backbone in any triglyceride intended for use as a propellant. Its abundance of hydroxyl and C-O bonds do not lend well to energy content or high flame temperature. Glycerol is difficult to burn in general. Have a look at the waste oil burner industry!

EDIT: Ahh, yes, amides are only very weakly basic. Amines are typical in hydrodesulfurization. Also, one might be trading the sulfurous reek for that wonderful fishy flavor.

As far as non-caustic and nicely soluble H2S scavengers, try NaNO2.

EDIT EDIT: No, I take that back! Ammonia salts of acids fall apart easily, so start with them. Just skip the conversion step to amides and use as-is. The conversion will happen during vulcanization and can go two ways: amide formation or entrapment of H2S, forming... err... ammonium hydrosulfide... Eh, on second thought I think it is going to positively reek no matter what!

EDIT 3: This is highly interesting: http://tenmasub.co.jp/en/products/sulfurchoride-factice.html

[Edited on 17-3-2015 by Praxichys]

deltaH - 17-3-2015 at 09:12

Quote: Originally posted by Praxichys

-- Speculation Alert --

I simply have my speculation alert permanently on display as my tag, it's easier that way

Quote: Originally posted by Praxichys

1. Degree of polymerization, and thus stiffness, is likely controlled by the number of unsaturated bonds in the starting oil.
....
The following is a table of various oils with their percentage of unsaturated bonds, from Wikipedia:

It's not just about content of polyunsaturated, the type of polyunsaturate is more important. You want an oil that is high in triple unsaturated fatty acids, not double (both are 'polyunsaturated') in order to have the property of being a decent drying oil and making good factice.

So for example, sunflower oil is very high is polyunsaturates because it is high in linoleic fatty acid derived triglyceride component, a double unsaturated, but it is not a drying oil and makes crap liquid factice (I made that mistake). Linseed oil is high in linolenic acid derived triglyceride (~52-55%), which is a triple unsaturated fatty acid, so it does dry to form rubbers and makes good factice. Another even better drying oil is tung oil, very high in alpha-eleosteric acid derived triglycerides (82%), another tripple double bond fatty acid.

Quote: Originally posted by Praxichys

As far as non-caustic and nicely soluble H2S scavengers, try NaNO2.

I don't think H2S is the problem, it's probably thiols, the smell is much to terrible to be 'just' H2S. It's more like H2S on steroids :mad:

Removing glycerine may help reduce odour a lot as I suspect it's half of the problem (a la simple thiols...)

PS. Yes the white factice's are nice, but requires sulfur monochloride to make

The whole point of this is to simplify propellants for the amateur.

PPS. On the bright side, the government will love this cause dogs would probably smell it being made from the next city (I'm reffering to the brown factice)

[Edited on 17-3-2015 by deltaH]

Fulmen - 17-3-2015 at 10:12

There is also the matter of conjugated vs nonconjugated bonds, not sure if that plays a role.

As for saponification, are we even sure that these acids or soaps will vulcanize just as the oils do?

deltaH - 17-3-2015 at 10:49

Whole linseeds are also sold by the packet as a health food these days. What about blending the whole linseed and then adding the other ingredients? All that fiber should stiffen the resulting factice a lot. If you're lucky and can find a bulk supplier of raw whole linseed, it might be fairly cheap (as opposed to heath food store prices which I find very inflated).

One might fake this effect by making use say blended newspaper and linseed oil for added stiffness. Hell, this is basically the propellant equivalent of linoleum flooring (made from linseed oil dipped cotton rags)

The carbohydrate content of the fibre might help the burn.

EDIT: Sorry keep saying linseed, for the whole seed, the name 'flax seed' is more appropriate.

The notion that you could simply blend flax seed, sulphur, potassium nitrate, then compress and bake to make a composite rocket fuel sounds mad though, I must admit

Warning: blending together may lead to spontaneous ignition, blend seperately!

[Edited on 17-3-2015 by deltaH]

Fulmen - 17-3-2015 at 11:57

I think we're far enough off the beaten path as it is

Good news: The MgO is done, 1 hour @400°C should be enough. I tried heating 10 parts rape seed oil with 1 part MgO, no visible reaction occurred. So I added 2 parts sulfur and continued heating. The MgO wasn't fine enough to stay in suspension, and the precipitate quickly turned black. I'm assuming some sulfides are formed. Continuing heating and stirring the oil turned dark brown and thickened within 5-10 minutes. This time the smell isn't as bad, smells more like elemental or burning sulfur rather than that smell of death I got the other day. Whether it is due to the MgO or more gentle heating I don't know.
After 30 minutes the factice was still liquid, so I turned off the heat and let it cool. It ended up as a semi-solid sticky goo, not far off from the previous result. I will try heating it further tomorrow while I dig for the linseed oil.

deltaH - 17-3-2015 at 12:09

Sounds very promising Fulmen. I'm VERY pleased to hear that the smell was toned done. I'm excited to hear about your linseed oil experiments. Best of luck with that!

Praxichys - 17-3-2015 at 12:14

How about this:

A saturated solution of sulfur is prepared in hot xylenes. Some linseed oil is heated to approximately the same temperature. The solid oxidizer is weighed, finely powdered, and warmed. All three ingredients are rapidly combined to form a dough, which is rammed into propellant cores. Vulcanization proceeds and the xylene is simultaneously baked out by holding the finished core in an oven until stiff.

The xylene carries the linseed oil and spreads it evenly throughout the oxidizer, much like petroleum ether can be used to spread PiB into RDX.

I did some math on the stoicheometry, and it appears the it may be difficult to get a thorough mix of the oxidizer/fuel binder.

About 92% of rapeseed oil is oleic acid, linoleic acid, and a-linolenic acid, all C18 fatty acids. The average molecular weight of the triglyceide is expressed as (C₃H₅)(C₁₈H₃₂O₂)₃, or C₅₇H₉₉O₆, MW 879g/mol.

The combustion of rapeseed oil therefore looks like this:

4 C₅₇H₉₉O₆ + 315 O₂ --> 228 CO₂ + 198 H₂O

I have compiled the following oxygen-balanced weight ratios for oxidizer to rapeseed oil:

Ammonium Nitrate - 7.17:1
Potassium Nitrate - 7.17:1
Sodium Nitrate - 6.10:1
Ammonium Perchlorate - 8.43:1

Note that these values ignore any sulfur content, which would cause them to increase.

Also note typical oxidizer to fuel ratios for various compositions:

Black powder, 75/15/10 - 3:1
Zinc/Sulfur - 2:1
APCP: 2.3:1

These do not look stoicheometric. Can ANFO be used as a rocket propellant? The AN version is like ANFO but with vegetable oil and a little sulfur.

deltaH - 17-3-2015 at 12:30

I like your out of the box thinking Praxichys, but I fear xylenes could cause the cast to mushroom out during baking due to vapour bubbles forming and expanding.

Fulmen also stated before that running fuel rich is better and also favours the cast.

[Edited on 17-3-2015 by deltaH]

Fulmen - 17-3-2015 at 13:43

Praxichys: Let's not get too carried away just yet. I have real doubts about this endeavor, but it peeked my curiosity so I just want to take a look at it.

Perhaps we're missing the elephant in the room, the drying oils themselves. Do we really need the sulfur at all, why not accelerate it's natural polymerization? Yes there are drying additives, but they all depend on oxygen as far as I can tell. Perhaps a peroxide accelerant?

Fulmen - 18-3-2015 at 07:21

Bad news first: No additional solidification from prolonged heating. So it looks like the edible oils are out. Also I'm unsure if this batch actually smells any better or I'm just getting accustomed to the smell.
It remelted upon heating and after 30 minutes it was still liquid. So after checking that there were no adverse reactions I added 20 parts KNO3 to the mix. It formed a dough-like pliable mass that would not sustain combustion when heated with a blow torch.

On the plus side I found the linseed oil, so that will be next on the list.

deltaH - 18-3-2015 at 08:07

Thanks for the update, but even from the literature, rapeseed oil didn't look very promising. The rapeseed versions looked like jello. Incidently, when you said rapeseed, did you mean off-the-shelf Canola oil specifically?

I'm holding thumbs for linseed oil. It would be cool if there was a way to easily separate out useless triglycerides, you know, saturated, monounsaturated and di-unsaturated. If I'm not mistaken, that makes up ~45% of linseed oil and will only detract from hardness since they can't vulcanise. I don't suppose simply leaving it in the freezer for a day will do the trick...

Fulmen - 18-3-2015 at 08:47

Not Canola, just a no-brand rape seed oil for cooking. Don't know if it matters.

The linseed test is under way, some preliminary observations: First off, the oil is an old bottle of unknown "boiled" quality, fresh or raw might behave differently.
Heating 10 parts with 1 MgO produced some slight foaming, I'm guessing it's due to water being produced from saponification. This subsided after a few minutes, producing a darker oil with little change in viscosity.
At this time 2 parts of sulfur was added. Within 10 minutes the mass had thickened to a rubbery dough, more solid than the cold RSO-product. Sadly the cold product has little strength, crumbling with little resistance when manipulated. I'll let it cool for a few hours and see how it behaves to reheating.

Bert - 18-3-2015 at 08:48

From personal experience, flammable oils, either of organic or mineral origin in VERY small percentages will greatly slow a solid fuel or other pyrotechnic mixture-

This is done deliberately to make "oiled stars" that are intended to smolder all the way back to the ground (or water... I would only fire these over a body of water, deep snow, etc.). A friend who was less cautious calls these "FSAFOYH" stars (as in "flaming shit falls on your head").

Some will add a % or two of oil in a fast evaporating solvent to black powder rocket fuels that are too fast burning for the intended motor size, then dry off the solvent. If done correctly, the remaining oil slows the fuel down just enough to prevent a CATO- add just a little bit more, and they sometimes won't leave the ground!

Fulmen - 18-3-2015 at 09:26

I know, it's the most likely explanation for the complete failure of the vulcanized RSO.

As for vulcanized linseed oil, I'm not seeing it. This stuff has no shear strength whatsoever, I see little hope of this working as a reliable binder.

deltaH - 18-3-2015 at 09:44

Pppft, that's disappointing. Fulmen are you heating this in a test tube over a flame? Any idea of the temperature?

Fulmen - 18-3-2015 at 09:49

No, I'm using a thermostatically controlled hotplate set at appr. 150°C. One could of course try to optimize the conditions but I think I'll leave that exercise for someone else.

deltaH - 18-3-2015 at 10:14

Thank your for your time and efforts, fulmen. It's greatly appreciated.

I think I might dabble with this a bit further. Will update here.

[Edited on 18-3-2015 by deltaH]

Fulmen - 18-3-2015 at 12:03

Go ahead, maybe you'll get lucky. It's not unreasonable to expect variations due to both methodology and raw materials, but for me that is a bit of a turnoff. It's like brand-specific recipes where no-one can tell you what makes that brand important. If you can't get that one you have to go through the pain of random testing. The sugar-based propellants greatest advantage is that they work with any brand of commonly available consumer products.
But from what I could gather factices often exhibit poor shear strength. Yet I read it was also used as a rubber substitute. Bit was that only as an dilutant or also as a replacement? If used as a pure substitute then clearly better results are possible to achieve.

deltaH - 19-3-2015 at 00:23

While luck plays a factor as with all things in life, product and formulation development is very tough. Something like this may takes months of research to perfect. I don't think it's going to be about brands used or anything like that, I just think the science is a lot more complex.

For example, I think the formation of either a magnesium or calcium soap is important, but also think that that will hardly proceed with MgO and ordinary oils, unless you cook it at very high temperatures for a day. If you look carefully at that African agricultural research paper attached earlier (Ebewele et al, 2013), you'll notice that the rubber seed oil they used had a ridiculously high content of free fatty acid, I think something like 38%. That is completely unusual for normal OTC and refined oils and this is also why simple MgO neutralised that particular oil easily. But when I tried to saponify sunflower oil low in free fatty acid using lime and heating, I did not achieve any significant conversion. So there is the first problem, saponification (hydrolysis of triglycerides) does not proceed easily with alkali earth oxides, while on the other hand, these react easily with free fatty acids. In the case of linseed oil, the free fatty acid content would be much much too low, so very little saponification would have happened under the conditions you were using. If it did, the oil would have gelled there and then, possibly even solidified. Then vulcanising would have hardened it even further. Anyway, there's a lot to explore here and many possibilities. It's not just about optimisation, it's about studying the system and solving its problems.

What I think I'd like to try first is saponifying linseed oil with lye by normal soap-making methods (and an OTC phase transfer catalyst) that I'm used to. Then I would neutralise it with hydrochloric acid to precipitate and salt out the free fatty acids. Those aught to easily react with MgO or lime at elevated temperature. They should also stink significantly less when vulcanising because you've purified it and removed glycerine. Ideally, one would distill the fatty acids under reduced pressure or with steam, but I don't have the apparatus for that. If one distilled it, you could ditch the useless saturated and monounsaturated fatty acids that detract from hardness.

Industry straight steam strips the starting oil to obtain fatty acids, relying on the high temperature of the superheated steam to hydrolyse and crack the oil, but that's not something the amateur couldn't easily set up, plus the initial stripped fatty acids have to be redistilled to isolate the desired fraction of polyunsaturates.

[Edited on 19-3-2015 by deltaH]

STEP 1: Saponification of linseed oil

deltaH - 20-3-2015 at 10:02

Bought a 750ml bottle of light brown raw linseed oil at my hardware store today. It was about halfway in cost between cooking oils and olive oil, so not too bad.

I dissolved 35g NaOH in 35g tap water with gentle swirling in a 500ml polypropylene plasticware with a good rubber sealed lid and side snap wings. Then 5ml didecyldimethylammonium chloride (30% w/w solution, black algaecide for pools) was added in one portion as phase transfer catalyst and formed a white milky precipitate (presumably sodium chloride). 250g Raw linseed (flax seed) oil was then quickly added to the very hot solution, the lid secured tightly and then contents was shook by hand, making sure to firmly hold the lid and base down in a pincer grasp because the pressure increases slightly. The hot emulsion was then shaken by hand at a leisurely pace for several minutes until it thickened (trace reached) and resembled mustard after which it was set aside to react further overnight.

I'm pleased with the saponification so far.

EDIT: I had a brainwave, I was going to acidify and isolate the fatty acids tomorrow, but I just realise that I can simply cook this soap up with a concentrated Epsom salt solution to form and salt out the magnesium soap directly (since it is insoluble). I can then mix this with catalyst, NaNO3 and sulphur, compress and then bake to vulcanise.

UPDATE: To quote fulmen, look like it's taking its sweet time :mad:

Next morning, it's a little firmer but still not fully saponified in my opinion. I'm going to put the container in a small dish with water and boil it slowly for a couple of hours to speed things up. Perhaps my phase transfer catalyst isn't working as well as I'd hoped.

[Edited on 21-3-2015 by deltaH]

deltaH - 21-3-2015 at 01:54

Quote: Originally posted by Bert

From personal experience, flammable oils, either of organic or mineral origin in VERY small percentages will greatly slow a solid fuel or other pyrotechnic mixture-

This is done deliberately to make "oiled stars" that are intended to smolder all the way back to the ground (or water... I would only fire these over a body of water, deep snow, etc.). A friend who was less cautious calls these "FSAFOYH" stars (as in "flaming shit falls on your head").

Some will add a % or two of oil in a fast evaporating solvent to black powder rocket fuels that are too fast burning for the intended motor size, then dry off the solvent. If done correctly, the remaining oil slows the fuel down just enough to prevent a CATO- add just a little bit more, and they sometimes won't leave the ground!

I'm hoping (though can't promise) to ditch the really inert waxy unsaponifiable matter, saturated fatty acids and maybe monounsaturates as well. Their soaps aren't very soluble, so when I boil up my saponified linseed mass, I should be able to skim them off before adding magnesium sulfate to precipitate the magnesium soaps.

I should be left with something enriched in polyunsaturates if all goes well (which it seldom does

) which should be far more reactive.

Finally, I have a bottle of ferric nitrate nonahydrate. I'm going to add a few percent to the final mix with sulfur and oxidiser. This should decompose on heating (during vulcanisation) to a ferric oxyhydroxide/sulfide that I'm hoping will serve as a cracking catalyst for the organics when burning. I'm borrowing here from industry that use 'iron muds' to crack very heavy petroleum oils/tar.

[Edited on 21-3-2015 by deltaH]

STEP 1: Saponification of linseed oil - UPDATE

deltaH - 21-3-2015 at 07:14

Yay, saponification complete, placing the PP container in simmering water for three hours did the trick and produced an interesting linseed oil soap... a first for me

Now on to salting out and Mg ion exchange with Epsom salt.

PHILOU Zrealone - 21-3-2015 at 09:51

Just a few side notes!
1°) Ca(OH)2 would also provide precipitated unsoluble soap and may be cheaper than Mg soap.
2°) Mixing cationic soap with anionic soap result in a waxy unsoluble precipitate and ruins the soap effect of both cationic and anionic surfactants.
(C10H21)2N(CH3)2Cl + NaO2C-R --> (C10H21)2N(CH3)2O2C-R+ NaCl
didecyldimethylammonium linseed-oleate
3°) It may be good to test for sorbic acid or sorbates with sulfur... sorbic acid is CH3-CH=CH-CH=CH-CO2H (2,4-hexadienoic acid) it contains two unsaturations and may lead to sulfide/disulfide crosslinkage.

[Edited on 21-3-2015 by PHILOU Zrealone]

STEP 2: Magnesium ion exchange and salting out

deltaH - 21-3-2015 at 10:08

[1] Simmered my linseed soap with 1000ml water for 90 minutes. Most of it dissolved, but a few gelatinous blobs remained insoluble.

[2] Carefully poured out the solution using a spoon to hold back the floating insoluble bits.

[3] The clear solution in a stainless steel bowl, hopefully somewhat enriched in unsaturated fatty acid soaps (wishful thinking

)

[4] Added 100g Epsom salt (MgSO4.7H2O) in one go into the hot soap solution while stirring gently. It immediately precipitated 'curds'.

[5] Carefully poured out the slightly milky liquid using a spoon to hold back the curds. I was careful to not squish the curds in the process as they were very soft and I wanted to maintain their granular form for washing. I washed twice with tap water and stirred very gently when washing.

[6] After my final wash and decant, I used my hands to compress the magnesium linolate precipitate. It felt like a very soft and fatty dough.

[7] Spread out the product on several sheet of newspaper to soak up the excess water. Some ink transfer occurred on the underside, but I'm not too bothered by that.

All-in-all, this was great fun!

[Edited on 22-3-2015 by deltaH]

deltaH - 21-3-2015 at 10:11

Quote: Originally posted by PHILOU Zrealone

Just a few side notes!
1°) Ca(OH)2 would also provide precipitated unsoluble soap and may be cheaper than Mg soap.
2°) Mixing cationic soap with anionic soap result in a waxy precipitate and ruins the soap effect of both cationic and anionic surfactants.
(C10H21)2N(CH3)2Cl + NaO2C-R --> (C10H21)2N(CH3)2O2C-R+ NaCl
didecyldimethylammonium linseed-oleate

[1] Yes, but I had a packet of Epsom salts for the bath that I never used

[2] I've experienced this with close to one-to-one mixes, but not so much with small amounts. I cannot know if this helped or not for sure without rigorous comparison with a control, but I figured it wouldn't hurt much to have a little in there in case it could help.

***********
I decided against letting the product dry out as the little bit on my hand started to go slightly tacky as it was drying and I was worried this was the beginning of radical polymerisation.

Most of the excess water had been absorbed into my newspaper anyhow, the remaining product resembled a soft dough with a similar light yellow colour. I transferred to a sandwich bag and keeping it closed with air squeezed out until I decide what to do with it exactly.

The last thing that I want is for it to become really hard and useless.

[Edited on 21-3-2015 by deltaH]

PHILOU Zrealone - 21-3-2015 at 10:37

Maybe the few unsoluble gunky blobs are from the DMDD-ammonium-lineseed oleate.

The DDMDD ammonium chloride as phase transfer is of no use because as soon as NaOH/water hydrolyses the oil, it forms a soluble anionic soap that will be the phase transfert catalyst increasing the saponification speed.

But DDMDD ammonium chloride might be a good idea (for a deviated project) in a 1/1 fashion with sodium lineseed oleate to get mineral-less (No Magnesium/No Calcium) factice rubber starting material?

deltaH - 21-3-2015 at 10:46

Quote:

Maybe the few unsoluble gunky blobs are from the DMDD-ammonium-lineseed oleate.

They were still soluble in fresh water and were soapy, like store bought transparent soap. While I cannot discount this for sure, it also resembled what I frequently observed with ordinary saponification of other oils, e.g. olive oil etc. There's always hard to dissolve blobs that are nevertheless soapy. I don't think this was the complex of the two as you say, but it could be so. It could also be simple saturation

Quote:

But DDMDD ammonium chloride might be a good idea (for a deviated project) in a 1/1 fashion with sodium lineseed oleate to get mineral-less (No Magnesium/No Calcium) factice rubber starting material?

The one-to-one aspect is not that great, with things like Mg and Ca, you have at least two unsaturated 'strings' to cross link. Also the DMDD is completely saturated and large, not that great for the hardness of the final product I think, nor reactivity. I'm really trying to maximise the degree of unsaturation as much as possible, in that respect, I'm pleased to see yellow colours

****************************

[Oh, forgot to mention that I don't think the magnesium linolate is totally insoluble... I managed to wash it off my hands fairly easily and it was soapy to the feel. It might be less soluble than sodium, but I wouldn't say insoluble, it's more like another kind of soap and very soft like an oily dough.]

EDIT: I take that back, some of it clinging to the pot was really hard to wash out, I think there was some residual sodium linolate in the paste that made it easier to dissolve.

There's probably a fair bit of moisture in there still and not to sure what to do about it. From its marvelous consistency, I'm very tempted for a step 3 to just add the other powdered dry ingredients (S + NaNO3 + Fe(NO3)3.9H2O) and 'knead the dough' before baking in a mold to set, but the water in there could cause problems.

A desiccator with inert atmosphere/vacuum would have been handy right about now

[Edited on 22-3-2015 by deltaH]

deltaH - 21-3-2015 at 23:21

I need some advice on my formulation stoichiometry for my step 3:

I've made a spreadsheet with the following design parameters:

[1] Amount of NaNO3 to target formation of CO and H2O from the fuel (in reality there will be some mix with H2 and CO2 because of the water-gas shift equilibrium and iron catalyst present which is active for this reaction). I'm using fulmen's suggestion to run fuel-rich, which I think is a great idea.

[2] Enough sulfur to form all Na2S from the NaNO3

...and assumed my magnesium linolate is in fact pure magnesium linolenate (the other fatty acids in there should make only minor differences to the final weight of oxidant required etc.)

Now for the ferric nitrate. In the presence of basic soap, it's not unreasonable to assume that the ions would swop to a degree, forming ferric linolate and magnesium nitrate. In a way I'm pleased about this if it happens as ferric linolate would be a three prong soap and so can result in a more cross-linked factice (harder?) as well as dispersing the iron catalyst better in the material to favour cracking of the oils.

This results in an iron mass fraction of 1.3%, but that will go up in drying. This seems like a reasonable number.

What are your thoughts/suggestions on my composition formulation I've laid out?

Factice propellant composition.JPG - 38kB

Simplifying, this rounds off to:

• 6 parts NaNO3
• 2 parts magnesium linolate
• 1 part sulfur
• 1 part ferric nitrate nonahydrate

all by mass.

Planning to grind a small amount of these together in a mortar and pestle and then see what to do next, compress and bake is one option. This is obviously not castable, would have to go the liquid free fatty acid route if one wanted to make something castable, but it's a good way to check what the final material would be like physically and if it will burn. Still worried about the water that needs to come off... hope that doesn't mess everything up.

***********
Just realised I should have salted out and ion-exchanged using ferric nitrate in step 2 to make ferric linolate directly, stupid of me :mad:

If I had some ferrous sulphate, even better, oh well, next batch...

This is the structure of the iron clusters in ferric acetate according to Wikipedia. This seems too good to be true for my materials, now I have to try to make ferric linoleate using my ferric nitrate to salt out.

That beast has six freakin' legs!!!

[Edited on 22-3-2015 by deltaH]

deltaH - 22-3-2015 at 05:32

Quote: Originally posted by PHILOU Zrealone

The DDMDD ammonium chloride as phase transfer is of no use because as soon as NaOH/water hydrolyses the oil, it forms a soluble anionic soap that will be the phase transfert catalyst increasing the saponification speed.

I'm making another batch of sodium 'linolate' because I want to try salting out with ferric nitrate this time to prepare ferric 'linolate'.

For comparison, I didn't use the quaternary ammonium salt this time around and indeed, while reaching trace was slower (about doubly so), there is no major reason to use it since it proceeds nevertheless, so you were right!

aga - 22-3-2015 at 07:47

I'd never heard of Factice until you started this thread. Thanks !

Trying it out (simple factice) was a little smelly and messy, and didn't work out too well.

Olive oil and Sunflower oil were used: 50g oil, 12.5g Sulphur, 5g Sodium Carbonate.
Air was bubbled through the oil for 15 minutes, then the oil heated to 140C, the reactants added, and the heat removed once the reaction kicked off.

Sunflower oil reacted a LOT faster than the olive oil.

Both results are a viscous orange/dark brown liquid. The sunflower version is a lot more viscous.

[Edited on 22-3-2015 by aga]

deltaH - 22-3-2015 at 08:08

Wow aga, I'm amazed you tolerated the smell of that so well!
Nice photo's BTW, you make tar look about as good as it possibly can look in your third photo :cool:

The olive oil one looks like crude oil (probably smells similar but much stronger) and the final one looks more like tar.
To produce rubbery factices, you really do need a 'drying oil', cooking oils just don't have enough linolenic acid derived triglycerides.

My second batch of sodium soap of linseed oil is nearly finished, about to do the 90 minute dissolution before attempting an iron ion exchange and salting out of ferric 'linolate'.

aga - 22-3-2015 at 08:23

Yeah, the smell is pretty 'orrible.

Doing this in an apartment would have the neighbours either calling the police, fire brigade, or possibly an Ambulance, thinking that if you naturally made that smell, you'd be seriously unwell.

blogfast25 - 22-3-2015 at 09:23

Quote: Originally posted by deltaH

My second batch of sodium soap of linseed oil is nearly finished, about to do the 90 minute dissolution before attempting an iron ion exchange and salting out of ferric 'linolate'.

What's the interest in ferric linolate?

Metacelsus - 22-3-2015 at 09:32

Iron(iii) accelerates the burn rate of solid rocket fuel. For example, the Space Shuttle boosters used it at 0.4%.

https://en.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_Boo...

[Edited on 22-3-2015 by Cheddite Cheese]

deltaH - 22-3-2015 at 09:38

Exactly Cheddite Cheese. I'm hoping to cross-link the ferric linolate with sulphur by heat treatment to make a factice, the iron is then already in there and nicely dispersed, plus the iron itself may help cross-links the polymer, see the structure of the ferric acetate I attached above, it has six 'legs' which in my case will be polyunsaturated fatty acids instead.

blogfast25 - 22-3-2015 at 09:48

As regards that phase transfer catalyst, any soap making crafts site will show you it isn't needed. Saponification with NaOH or KOH takes a while but proceeds well and to completion, with just about any triglyceride. I prepared crude oleic acid that way, years ago.

Good luck with vulcanising your mixture of ferric linolate, NaNO3 and sulphur, though! Make sure you don't blow yourself up...

[Edited on 22-3-2015 by blogfast25]

STEP 2b: Iron ion exchange and salting out with ferric nitrate

deltaH - 22-3-2015 at 10:10

The ferric nitrate didn't yield as practical a result as the magnesium sulphate did.

The product appears to be a semi-fluid and the solution remaining still appears quite red. Not so sure what's going on here. I think the salting out effect is not working as well with the nitrate as it did for sulphate, but it worked in part, so letting it cool and will try to isolate the red-brown semifluid gloop that's floating on top. Definitely not as well behaved as the magnesium sulphate salting out.
Perhaps this would have worked better with ferrous sulphate?

In some way, this gloop resembles the oil dough consistency of the magnesium 'linolate', but it's so soft that it's actually runny. Seems like the higher the cation charge, the softer the resulting polyunsaturated soap, which makes sense.

I think I'm going to put this into my freezer to see if I can harden the ferric linolate... it's hard to work with it in this thick semi-fluid gloop state.

Interestingly, this might actually be close to a castable material!

[Edited on 22-3-2015 by deltaH]

blogfast25 - 22-3-2015 at 10:29

Quote: Originally posted by deltaH

The product appears to be a semi-fluid and the solution remaining still appears quite red. Not so sure what's going on here. I think the salting out effect is not working as well with the nitrate as it did for sulphate, but it worked in part, so letting it cool and will try to isolate the red-brown semifluid gloop that's floating on top. Definitely not as well behaved as the magnesium sulphate salting out.
Perhaps this would have worked better with ferrous sulphate?

Have you taken into account just how insoluble Fe(OH)3 is? Depending on concentration it starts precipitating from pH 4 to 5.

I bet part of your solids is Fe(OH)3, perhaps part of it in the peptised form.

Perhaps using a ferrous salt, followed by air oxidation of the 'ferrous linolate' would work better.

Alternatively use much smaller amounts of iron, it's supposed to act as a catalyst in the combustion, I think? If so, large amounts would not be necessary.

[Edited on 22-3-2015 by blogfast25]

deltaH - 22-3-2015 at 10:48

Thanks blogfast for the suggestions. I have an excess of ferric nitrate in there since I used 100g and there once again remained a fair amount of insoluble sodium linolate behind when I dissolved it in the step prior, so the pH of the solution is acidic. I'm relying on the insolubility of the product to force it out of solution.

It looks like it worked, it's just that the physical form of the product makes it cumbersome to separate, it's a runny gloop, but low temperature might help a lot (freezer). If I can just get it to firm up a little, I can manipulate it better and wash.

I definitely think using ferrous sulphate is the way to go, it should ion exchange and salt out in a similar fashion to what the magnesium suphate did, I just didn't have any on hand, but had the nitrate :mad:

In the end, it should matter what oxidation state the iron's in, the active catalyst I imagine would probably be reduced iron anyhow. I want a lot in there because the iron is going to be a lot less active with all that sulphur that probably poisons it. That said... I do know that ferric oxides speed up the burn of sugar+sulphur+saltpeter from personal experience, in-spite of the sulphur, but again, I used a few percent there, not hundreds of ppm's as one would normally work a catalyst.

blogfast25 - 22-3-2015 at 11:02

I've not read this thread from A to Z so I might be b*llshitting here but unintentionally.

Wouldn't it be simpler and more controllable to isolate the linolenic acid, dry it properly and then thoroughly mix in the sulphur, 'active' ferric oxide and sodium nitrate? Then mould and crosslink?

That would give far more control over the actual composition of the propellant, I think.

[Edited on 22-3-2015 by blogfast25]

deltaH - 22-3-2015 at 11:13

Yes, that was the original plan of sorts, but one of the problems with factice rubber is that it's soft. I found a paper on the first page of this thread that used magnesium oxide in the factice formulation to make a harder factice, so I hypothesised that the harder factice was because a magnesium soap was forming which then also vulcanised by way of the double bonds... a double whammy.

I just figured that I could make a reasonably pure magnesium soap off the bat instead of isolating the free fatty acids first and then using magnesium oxide, but ultimately, the free acid route is the route to go for a castable formulation.

However, the iron soap is changing matters, since the ferric linolate is runny, it might be castable as is. Anyhow, early days and lots of work in store. The ferric linolate may also benefit from a magnesium oxide addition if it has a high fatty acid content to it in terms of hardening the final factice product.

[Edited on 22-3-2015 by deltaH]

blogfast25 - 22-3-2015 at 11:44

Quote: Originally posted by deltaH

However, the iron soap is changing matters, since the ferric linolate is runny, it might be castable as is. Anyhow, early days and lots of work in store.

But it still contains loads of water too. Even if, as I assume, you started from pure ferric nitrate nonahydrate (and not a solution of it). So what will it be like when it's been dried?

Couldn't castability be regulated with small additions of a highly oxidisable oil like light mineral (paraffinic) oil?

deltaH - 22-3-2015 at 11:59

Praxichys mentioned using xylenes as a diluent on page 2. I'm not a fan of the paraffins, I think they will slow down the burn as Bert mentions somewhere thereabouts too.

Yes, the water may be a problem, particularly for the baking stage, as it might mushroom out the cast.

I'm thinking it might be carefully heat treated first to remove the water... like one would normally dry an oil. It is a semi-liquid after all, should be no problem to heat to around 100°C and hold for 30 minutes. I don't think it will froth because it seems to behave more like a hydrocarbon and less like a soap. I think it doesn't have the right shape to be a surfactant.

In fact, I'm probably going to boil down this mess I made to isolate everything and pray it doesn't polymerise, instead of sticking it in the freezer. It's going to contain sodium nitrate, but I'm adding more later anyhow and I know how much is in there which is what really matters

[Edited on 22-3-2015 by deltaH]

blogfast25 - 22-3-2015 at 12:53

Quote: Originally posted by Bert

From personal experience, flammable oils, either of organic or mineral origin in VERY small percentages will greatly slow a solid fuel or other pyrotechnic mixture-

Hmmm... the backbone of your linolenic acid is quite paraffinic too!

aga - 22-3-2015 at 14:05

Sorry if this is not directly releated to the OP, yet i would like to succeed in making Factice that can be removed from a pot as lump, rather than having beakers full of sticky brown goop.

Which Oil stands the best chance of success ?

Linseed ?

blogfast25 - 22-3-2015 at 14:21

This post has the unsaturation levels of several oils:

http://www.sciencemadness.org/talk/viewthread.php?tid=61792&...

Linseed oil should work well because of the high content of polyunsaturated fatty acids (linolenic acid in this case). It's also fairly OTC.

In the *.pdf linked to above (Factice from Oil Mixtures, Selim M. Erhan and Robert Kleiman) recommends 20 parts of sulphur per hundred parts of oil, cook for 40 minutes at 180 C.

[Edited on 22-3-2015 by blogfast25]

aga - 22-3-2015 at 14:36

Sorry. I missed that.

Thanks for the reference.

I'll get some Linseed oil and hopefully make a beaker less dirty next time.

Wife wasn't too happy about the plates i used, and as a bonus, i was so engrossed that i forgot about the new kettle, which melted onto the gas hob for an hour or two.

Thankfully the plastics were mostly Carbon by the time i went inside and noticed.

deltaH - 22-3-2015 at 14:45

Yes if you want rubbery stuff, you have to use a so-called 'drying oil', the most common OTC one is linseed, also called flax seed oil in health shops (though very pricey from there). Another one that is available from selected hardware store is Tung oil or 'china wood oil', that's probably the best, 80+% alpha-eleosteric acid (another triply unsaturated fatty acid).

I've said it before and I'll say it again, if an oil is high in polyunsaturated, it's not necessarily good for this, because linoleic acid for example (found abundantly in sunflower oil), with two double bonds IS a polyunsaturated, but it sucks at making factice, you really need an oil high in linolenic acid or another triply unsaturated fatty acid, specifically.

I strongly advise making soaps from the oils first and ditching the glycerine, I have a strong suspicion that it's the main culprit for making the severest stinks by way of volatile thiols. Also the making of a soap also reduces the volatility of the fatty acid, particularly with Mg and Ca, this also helps.

[Edited on 22-3-2015 by deltaH]

blogfast25 - 22-3-2015 at 14:51

In the *.pdf linked to somewhere above (Factice from Oil Mixtures, Selim M. Erhan and Robert Kleiman) recommends 20 parts (!) of sulphur per 100 parts of oil, cook for 40 minutes at 180 C.

[Edited on 22-3-2015 by blogfast25]

aga - 22-3-2015 at 14:53

OK.

So more sunflower oil, saponify, then go for the Factice ?

I feel a bit silly here, as i'm not aiming for what your OP is after, just a solid Factice.

deltaH - 22-3-2015 at 14:55

No not sunflower oil, that doesn't make a rubber.

deltaH - 22-3-2015 at 14:57

Yes saponify linseed oil first with lye, then boil up to dissolve most of the soap, then use magnesium sulfate (Epsom salts) to salt out and produce the magnesium linolate that you can use to make factice. It should be far less stinky, but that is to be confirmed

[Edited on 22-3-2015 by deltaH]

blogfast25 - 22-3-2015 at 15:05

Quote: Originally posted by deltaH

I strongly advise making soaps from the oils first and ditching the glycerine, I have a strong suspicion that it's the main culprit for making the severest stinks by way of volatile thiols. Also the making of a soap also reduces the volatility of the fatty acid, particularly with Mg and Ca, this also helps.

I doubt is glycerol has much to do with it. I worked for years in material development, including oodles of sulphur vulcanised rubbers. Well, even these glycerol-free processes stink, even though the raw materials are of very high MW.

Model studies of very low molecular weight dienes, sulphur vulcanised with accelerators, showed tens of sulphur bearing structures and byproducts to be the reaction product mix. And these stink to high heaven, as we know.

I also kind of fail to see how sulphur would affect the ester bond.

Factice producers use the oil rather than the fatty acids because a higher viscosity gel is obtained with the oil. Or so I've read...

Perhaps we should see what happens if a methyl fatty acid ester is heated with sulphur?

[Edited on 22-3-2015 by blogfast25]

aga - 22-3-2015 at 15:10

Sounds like i have to get some Linseed oil and do a whole series of experiments.

Reminds me of the CHRIS25 Aluminium Sulphate Saga.

Well, we succeeded on that one, so i guess it can be done.

deltaH - 22-3-2015 at 15:12

Quote: Originally posted by blogfast25

Quote: Originally posted by deltaH

At high temperatures triglycerides crack and release small amounts of glycerine which can then react with sulfur to make water and thiols, at least in theory....

Industrial factice is not necessarily a good rubber, it's blended with normal rubber to give a nice finish to it, that's why the industrial ones can be made from things like rapeseed oil, that gives gelatinous stuff, but not what we're after.

A free fatty acid if it's linolenic acid has only three doubly bonds to react with sulphur, but magnesium linolenate has six, so that's why the soaps are harder. The Ebewele paper on page 1 has the proof of the pudding.

[Edited on 22-3-2015 by deltaH]

deltaH - 22-3-2015 at 15:15

Quote: Originally posted by aga

Sounds like i have to get some Linseed oil and do a whole series of experiments.

Reminds me of the CHRIS25 Aluminium Sulphate Saga.

Well, we succeeded on that one, so i guess it can be done.

It's really easy actually, there's a step by step photo essay on page three for making the magnesium 'linolate'

All you need is linseed oil, lye and Epsom salts, all OTC.

[Edited on 22-3-2015 by deltaH]

aga - 22-3-2015 at 15:24

Got them all, apart from Linseed Oil.

Acquistion expedition tomorrow.

blogfast25 - 22-3-2015 at 15:30

An important point is like other vegetable oils/animal fats, linseed oil is not a pure trigycleride.

From Wiki (composition of linseed oil)

Quote:

The triply unsaturated α-linolenic acid (51.9-55.2%),
The saturated acids palmitic acid (about 7%) and stearic acid (3.4-4.6%),
The monounsaturated oleic acid (18.5-22.6%),
The doubly unsaturated linoleic acid (14.2-17%).

So saponifying linseed oil does not strictly yield a 'linolate' but rather a mix of soaps.

And, based on their fatty acid profiles I'm still at a loss why linseed oil does gel with (a lot of) sulphur but sunflower oil does not.

aga - 22-3-2015 at 15:38

Well, we all have to learn.

Best thing is to mess with stuff and see how it behaves.

blogfast25 - 22-3-2015 at 15:40

Quote: Originally posted by deltaH

Industrial factice isn't really rubber at all, it's MW is far too low for that. Good quality rubber has tensile strength of up to 20 MPa, rubber factices you can slice with a knife like butter. We did use to add factices to rubber compounds, mainly for extruded goods.

Rubber factices are quite low MW, if they weren't you could never incorporate them into green (uncured) rubber compounds. 'Gel factice' would be a better term than 'rubber factice'.

As the C=O, C-O and H-O bonds are all stronger than their sulphur equivalents, I think trigyceride esters should be quite resistant to attack by sulphur, except of course for those double bonds.

[Edited on 23-3-2015 by blogfast25]

blogfast25 - 22-3-2015 at 16:31

Quote: Originally posted by deltaH

The Ebewele paper on page 1 has the proof of the pudding.

Actually, assuming we're talking about the same paper:

Polymer processing aid from rubber seed oil, a renewable resource: Preparation and characterization. R. O. Ebewele1, A. F. Iyayi2*, F. K. Hymore3, S. O. Ohikhena4, P. O. Akpaka2 and U. Ukpeoyibo2

...then it does nothing of the sort. The paper isn't concerned with soaps and uses only rubber seed oil (RSO) in its experiments, not soaps of it, magnesium or other.

It does evaluate MgO at 10 parts per 100 parts of RSO, as an accelerator/modifier in the vulcanisation of RSO.

I'm surprised they don't seem to realise that in sulphur vulcanisation of rubber, zinc oxide (ZnO) is considered the invaluable and indispensable component. No sulphur vulcanising system goes without 5 to 10 parts of ZnO, per hundred parts of rubber.

So that might be something to consider, to improve crosslinking and obtain a simpler (read: shorter S links) crosslink network.

[Edited on 23-3-2015 by blogfast25]

deltaH - 22-3-2015 at 21:16

Quote: Originally posted by blogfast25

'Linolate' is my made up word for soaps of linseed (of all fatty acids), which is why I try to enclose it in quotes. Linolenate, linoleate, palmitate etc. on the other hand, is specific and real (referring to their respective acids) and so magnesium linolenate is a major component of a magnesium 'linolate'. It's a bit confusing, sorry

As for why linseed oil works better, I think that there are more 'sites' for vulcanisation with the triple unsaturated fatty acid oils and so more chance to have continuity in cross links between sulphur chains across the polymer network as a whole and so a more rigid structure.

Quote: Originally posted by blogfast25

Quote: Originally posted by deltaH

The Ebewele paper on page 1 has the proof of the pudding.

The devil's in the details blogfast

I've mentioned earlier in this thread that I noticed in that paper that their rubber seed oil is unusual in that it has a very high content of free fatty acids (FFA), some 38% in fact (it's in the 'materials and methods' section), so yes, mixing that with MgO and cooking up would make the Mg soap. It's a simple neutralisation reaction, not saponification, that proceeds easily. I also made the point that our everyday oils are typically quite low in FFA's by comparison and so replied to fullen's posts that I didn't think he achieved any significant saponification when he simply heated MgO with rapeseed and linseed oils because those don't contain such large amounts of FFAs and require traditional saponification methods if you want to convert them fully to Mg soaps.

Look, I might be barking up the wrong tree here with working with the Mg soaps, but I have a hunch they might (a) help to reduce the stench and (b) make a harder factice. This is hypothetical, of course, which is why I am doing the experiments to see...

The ZnO you speak of, does it have to be freshly precipitated high surface area stuff? I still have lots of ZnO left over from my experiments with zincates, it's calcined pharma grade. It seemed rather inert and I struggled to dissolve it as is in sodium hydroxide solutions back then. It did, however, dissolve in acid, so in you experience, do you think that would work as is, because I'd be very happy to use it

[Edited on 23-3-2015 by deltaH]

deltaH - 23-3-2015 at 02:36

Managed to boil my ferric 'linolate' only for a few minutes before masses of dark and viscous red oil prevented me from continuing. Because of it's viscosity, it started to balloon instead of releasing the water vapour bubbles nicely. Looked like boiling lava mounds :mad:

It smells and dries very much like wood varnish... I really wish I owned a garage with a garage door that needed painting

Anyhow, I get the feeling this red oil is just ITCHING to harden up, I just need to get the bubbles out and to separate the water entrapped in it. I'm not keen to dilute it to drop the viscosity, sigh... it's a pain in the ass.

hyfalcon - 23-3-2015 at 04:49

Try vacuum.

deltaH - 23-3-2015 at 06:13

Finally got some sulphur and have two substrates to play with... stinky time

deltaH - 23-3-2015 at 08:37

UPDATE: Okay, mixed 50 pho sulfur (yes I know it's very high, but about what would be necessary for a propellant) with my nice yellow magnesium linolate paste. Made a butter like material, but still very soft, like an oily paste. I placed a pea-sized bit on a SS spoon and attempted to gently/gradually heat it over a flame.

This produced an intense sulfur smell and small amounts of white fume, exactly as melting sulfur over a flame smells and looks. I'm pleased to report that it didn't produce any nasty organosulfur type smells, just strong sulfur fumes. It took me back to my childhood, making black powder.

I struggled to cook the factice in my spoon, the back charred while the top turned dark brown, but soon everything was char :mad:

Overall, it looks promising in terms of smell reduction, but a pea-sized experiment won't do. I'm less scared of it now that I've established it appears like 'just' sulfur fumes coming off. The residue wasn't too smelly either, so I'm really happy about that.

I need to buy some test tubes and repeat with slightly more of the 'special butter'

and try to heat it more slowly this time around. I have a high-temperature thermometer, beaker and gauze, so I might use a small oil bath and target 160°C and immerse the test tube into it with some foil over the top. If the factice gets hard and stuck, I can always smash the test tube to free the melt.

I'll be heating incrementally and taking some photos.

[Edited on 23-3-2015 by deltaH]

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