Sciencemadness Discussion Board

Styrofoam - Lets reprocesses it

Intergalactic_Captain - 31-3-2019 at 22:55

Polystyrene comes up on this board from time to time, but usually not with the intent of reusing it in its original form. My primary interest in this is lost-foam casting - I'm sure a few of you guys are familiar with the process. Cutting foam is easy enough, but what if I wanted a molding setup?

The obvious solution to this is to just buy expandable polystyrene beads, and, as you may guess, expand them in something resembling the industrial methods. Steam, age, mold, steam, age - Simple. Except NOBODY sells the fuckers! Well, with the exception of one guy I found on ebay, but after researching the production process I have a better understanding of why nobody sells them, at least in non-industrial quantities.

Here's my thought - The stuff (expanded polystyrene) is all over the place already. From a recycling standpoint, and yes, I pored over that too, the main reason it isn't done is density - at ~98% air, it's not worth enough to justify the collection and transportation infrastructures versus just making more. So we throw it out, and pay no attention to the fact that this stuff is not only a potentially useful material, much less how much space it might represent in our landfills.

I'm no bleeding heart, so take all the above with a grain of salt - Lost-foam casting remedies the volume problem by deflagration - quite spectacularly.

So where am I going with this? Well, first and foremost, I want expandable polystyrene beads. If I ran a factory, no problem - buy it by the gaylord and run it by the usage-date. Why? Blowing agent volatility. My best guess, again going from a couple weeks of random research, is that the primary reason for inaccessibility to amateurs is a matter of solvent volatility.
Blowing agent evaporates, unusable product, dissatisfied customer.
Not enough money to pay your EPA fines? Sorry, you're done. Less capital than either of those options? Hmm. . . Everything I've found says that pentanes are preferred, except for niche purposes. CFC's are an environmental nightmare, propane and butane are (more) volatile, and higher alkanes are less volatile. Specialty purchase, then, but at ~5)+-2%w/w, not exactly prohibitive. Sooo...

How's it made? Aqueous polymerisation, some sort of filtration, blowing-agent impregnation, another aqueous stage for bead formation, more filtration, and. . .

Then there's this - US Patent 7776244B2 - Can we just skip the above, melt some polystyrene, add some pentane, and extrude it?

edit - remove edit marker

[Edited on 4-1-19 by Intergalactic_Captain]

Intergalactic_Captain - 1-4-2019 at 00:31

So just for shits and giggles the other night, I decided to revisit an old experiment. As an avid dumpster diver, I have always had a certain respect for the amount of "stuff" I throw out. As such, styrofoam of any sort almost always gets set aside for better uses. Some time ago, the pile got too large, but disposing of it was not an option - wind plus very light garbage bags equals problems for everyone. So, having some toluene on hand, I dissolved something like three cubic yards into a more managable form for future use.

What to do? Well, long story short, my initial experiments were abject failures. My thoughts were that by stirring my solution in water, I might be able to form beads, or at the very least emulsify it. No go. How about heat? No, little better, but not much. Then the breakthrough moment - Let's subject a bit of the "emulsified" goo to vacuum, and see what happens - nothing. Well, not exactly nothing - I suppose if I were a special effects technician in the pornographic industry, I might just be able to retire at this point - but that is not the goal here.

So, what did I learn?

1 - No cosolvent for bead formation. Search as many patents as you want, the initial polymerisation seems to be styrene monomer + initiator + water, process, and that's it.

2 - Stronger stirring? I was using a highly unoptimised magnetic setup. In the back of my mind, I imagine that high-speed, high-torque mechanical stirring at 100degC in water, with a polystyrene/toluene mix dripped in via burette or similar might work.

3 - I know precisesly dick about polymer chemistry - This one is not new, but just a reminder to myself. My theory is, being a simple, non-crossed system, once the initial reaction is terminated, the polymer chain should be chemically stable - Provided said chain is not exposed to undue chemical or mechanical stresses, it should be otherwise, for lack of a better term, plastic, correct?

Ok, lets get to processes. . .

1 - Raw Material - There are a couple commercial operations out there that go by compaction - Not going with that here. Not primarily, at least. Ultimately a solvent system will be needed to get the last of the air out. Failing that, compaction followed by direct melting, perhaps?

2 - Solvents - I used toluene because it was on hand at the time. Obviously, not the best choice. Limonene seems to be the solvent of choice from both the industrial and hobbyist standpoints, but I cant seem to finger whether this is for "green" reasons or simple availibility. In either case, it's a moot point - we need a clean resin with a reasonable expenditure of energy. My thought is lower alkanes are the way to go.

3 - Drying - Since we're starting with the polymer, screw the polymerisation. We need to dry our goo. Atmospheric, forced air, vacuum, etc? Winter just threw another jab here so it will be a couple days, but I plan on pouring a ~1mm film of my goo and leaving it to dry unassisted.

4 - Granulate - I almost hesitated adding this, but it will be an important step. Now that the goo has dried into a sheet, we need to knock it down to a usable form. Alternatively, or preferrably, our goo would be extruded and chopped before drying in order to conserve operations.

5 - Impregnate - Now here's where things get interesting. Our primary concern is that, for all intents and purposes, we are at the same point in our process as a manufacturer would be after the first sieving of resin beads from the polymerisation tank. Our only difference is that our resin is not "wet," and it may or may not already be in a granular form. Pretty much every source states the same clearly vague process - the blowing agent is introduced to the resin, in a molten state (100degC), and the mix is then processed in whatever manner. The Fuck?

Simple enough, I figure, except for number 5. My best guess as to how to do this at home would be a bomb-type pressure vessel.

1 - Simple bomb-type setup. Cap on top, valve on bottom, components in, shake/heat, impregnated resin out.

2 - Same as 1, but with a die plate as described in the mentioned patent. A simple slicing mechanism for sizing.

3 - Some kind of stirred autoclave. Necessary, perhaps? None of the patents I've read give any indication to temperature/pressure, but heavily imply the necessity of solution polymerisation, hence stirring - but then, patents are notoriously obscure.

So, do we have a project here? Or is this just another one of my ultimately futile quests? I say we make some EPS beads.

RedDwarf - 1-4-2019 at 05:14

Idle thoughts of an idle fellow... why not combine 3 and 4 by trying spray drying/ fluidised bed?
Also in terms of step 5 - impregnation, what about using the approach of the urethane foam diy cans and just mix blowing agent into batch of molten polymer at last minute (under pressure) and then inject into mould at low pressure so blowing agent expands at that point? That way you don't have to worry about a process to keep blowing agent in granules during storage.
If you want me to elaborate more about how it might be done on an amateur/batch basis let me know.

Pyro_cat - 20-8-2019 at 23:41

I had an idea to make ice in the winter to use for AC in the summer and to make a massive cooler I was also thinking about recycling Styrofoam here on this thread

[Edited on 21-8-2019 by Pyro_cat]