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deltaH
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Factice rubber-based propellants from vegetable oils
'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]
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kecskesajt
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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.
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deltaH
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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]
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Fulmen
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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.
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deltaH
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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]
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Fulmen
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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.
We're not banging rocks together here. We know how to put a man back together.
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deltaH
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"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 
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Fulmen
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This PDF looks relevant: www.ijarnp.org/index.php/ijarnp/article/download/212/pdf_6
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deltaH
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Some more literature... discusses some activators and accelerators useful for making factice.
Attachment: Rubber seed factice.pdf (323kB)
This file has been downloaded 880 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]
Ah ok, here's an in-depth article about linseed oil factice.
Attachment: Linseed factice article.pdf (378kB)
This file has been downloaded 585 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]
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Fulmen
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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.
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deltaH
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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]
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Fulmen
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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]
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deltaH
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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
[Edited on 15-3-2015 by deltaH]
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Fulmen
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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.
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PHILOU Zrealone
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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]
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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deltaH
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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]
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Fulmen
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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.
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deltaH
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...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]
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Fulmen
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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]
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PHILOU Zrealone
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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, ...)
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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deltaH
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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
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Fulmen
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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.
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deltaH
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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]
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PHILOU Zrealone
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| 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
PH Z (PHILOU Zrealone)
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deltaH
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One has to be careful with the use of sulfur scavengers lest it reverses the vulcanisation
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