Polystyrene based cast able fuel

[gtvpo]

So, I recently wanted to find a use for ammonium nitrate in rocketry (Because I like how cheap it is, if I'm honest) and ammonpulver is somewhat underwhelming in my current state of not having proper milling set up for getting the chunks of charcoal down as well as the AN.

 

But, I recently did some basic stoichiometry to see if I could find a formula for the combustion of polystyrene with AN as an oxidizer. (I'd recently figured out that polystyrene dissolved in toluene makes a fairly decent binder. I then, of course, got curious and tried to see what I could do with that knowledge) so, my basic formula was born

 

76 grams AN, 15.6 grams PS.

 

one gram of a catalyst is also provided for, and I tried salt for the first batch (Copper and iron oxide are the ideas for future batches)

 

the procedure for making it is to finely powder the AN, then dissolve the polystyrene into toluene (Or another solvent) for toluene, I found about 50 milliliters was plenty, but eyeballing it is fine.

 

Once it's been mixed thoroughly, it can be left to dry and once it's solid and somewhat crumbly, it's done.

 

It didn't work perfectly. It burned like normal polystyrene and then suddenly, once there was a puddle of AN and PS mixed in liquid state, it burned quickly (Faster than ammonpulver does, slower than meshed BP) with a small yellow flame over its surface. I'm thinking that I messed up my chemistry, and that's what I was hoping you guys (Who are all way better at practical chemistry than I am) could help out with!

 

So here's the working formula:

 

20NH4NO3, + 3C8H8 > 20NH4 + 10N2 + 12H2O + 24CO2

 

I'm fairly certain that my problem is on the products side. If my balance is wrong, and that's actually the only problem, this could be really easy to fix.

 

However, I doubt that. In the meantime, I kind of want to try out a second fuel being added (Charcoal dust, because if it ain't broke don't fix it, and later sulfur, because of the same reason)

 

Any help is massively appreciated! If this can be solved out into something workable, people might be able to make rocket fuel out of fertilizer, trash, and paint thinner... Or just have some fun with deflagration.

[AzoMittle]

Polystyrene dissolves easily but redries to a crumbly state, like you said.

 

I would recommend switching to ABS (used for 3D printing). It is much tougher, does not crumble, but does not dissolve easily either; talking with 3D printing people, what they usually do to make 'ABS glue' is to leave it in a jar overnight with a mix of organic solvents. I would also suggest adding half of the weight of your binder (PS or ABS) with a Dibutyl Pthalate (DBP), ex. 12% ABS gets 6% DBP, add this while binder is in a slurry state, and before adding dry components.

 

A few percent of charcoal or lampblack should help to reabsorb some of the heat. Think of parked cars out in the sun, which will get hotter the black car or the silver car? Oversimplifying but you get the point.

 

edit: Your 'puddle then burst into flames' comment makes me think it wasn't mixed well enough. This stuff looks like it is mixed well, until it dries, then it becomes obvious it isn't; this could be due to either under-mixing or the contents settling before it is dry.

Edited June 18, 2016 by AzoMittle

[gtvpo]

That's a large part of my theory on the issues. And The idea was to make it from trash from the start (Though I will totally try ABS, don't get me wrong)

 

Since I'm testing multiple things, I might just try the R-Candy method of mixing, just for the heck of it

 

Where exactly would I source the DBP, by the way? it's looking quite expensive, though I won't deny having a plastizer does have some great benefits.

Also, as a former LEGO junkie, I've got some experience with ABS and I must say DBP plasticization isn't necessary for rubbery consistencies prefered in Composite propellants, the addition of a rubber can also work if the thermoplastic method is used. Might be worth some looking into.

 

Anyways, I'll get some videos up of the stuff burning and try milling the AN a bit better beforehand. Thanks for the advice!

[Mike]

Touluene is drykng out quite sllw. Maybe you should think about using a faster evaporating solvent, to prevent seperation of your contents.

[gtvpo]

While it does dry slowly, it is currently my only pure covalent solvent. I'm planning on grabbing some acetone and maybe another solvent at some point, but in the meantime, it works. And I have a gallon of it.

[PIL]

AN based propellant requires a metal fuel to regulate and sustain its combustion.You may add coated magnesium or fine magnalium powder. Catalyst such as ammonium dichromate is necessary as well.

I don't suggest using a solvent during the casting process because it leaves bubbles in the grain or creates gaps around the grain, which can cause a explosion. Polyurethane glue (polyol and isocyanate) seems to be the best option.

[Mumbles]

There are indeed problems with your balanced formula. NH4 is not a discrete neutral molecule. The ammonium cation will burn to water and nitrogen under ideal circumstances. This is what I came up with. You may want to double check though. I haven't had any coffee yet today and am kind of dragging.

 

20 NH4NO3 + (C8H8)n ---> 20 N2 + 44 H2O + 8 CO2

 

You might be fighting against other issues. Salt is not a catalyst. If anything it's a burn retardant. Ammonium nitrate is not an overly vigorous oxidizer in deflagrating compositions. I don't know much about polystyrene as a fuel, although my impression is that it's not great.

[gtvpo]

I'll chuck the salt then. Hah, Can't believe the ammonia derp though lol. I just mainly wanted to try it out, just FYI! This isn't really supposed to be a super-useful fuel.

 

I'm going to try adding carbon, as well, so I'm going to add the bits for that as a separate reaction and then just mix the stuff for that into the resin-y stuff.

 

To be clear: This isn't supposed to be an awesome rocket fuel, its just being tested to see if it works at all, for fun, and because the chemistry looked cool.