Introduction: Recycling Styrofoam (EPS) Into Useable Castable Styrene Plastic at Home

About: Im a bit of a geek of all trades. Of late most of my free energy has going into Making sure our hacker/makerspace is awesome! Come check us out!

Scope of the project and feature creep:

Recycle small old Expanded Polystyrene foam insulation coolers I get monthly with a medication. Our city has no program that accepts EPS, and so I looked into some experiments with it, and in the process come up with a 'Easy' technique to Recycle EPS (Expanded Polystyrene Foam) not only reducing its size, but also making it into something usable/useful (im calling it “Maker Goop” for now). In a relatively safe and health conscious way.

‘Maker Goop’ Can be handy for making small plastic parts, castings, or just to make the EPS a flowable product for makers, or for Recyclers which could have the solvents extracted and reused commercially, or burned (as is done in the EU for power. It does emit co2 and water vapor and not much else.)

Below are some notes on my experiments on found on Degasifying the EPS (EPS is 90-99% empty space, and 1%-10% Polystyrene. First steps were to isolate a way to turn it from foam into a liquid to both save space, and make it useable. This is also the first step in commercial recycling too. But at this point i'm experimenting on the small scale for home/hobby reuse.

And I really look forward to seeing what people do with their own nearly free 'Maker Goop'!

Step 1: Materials

You will need the following:

  1. A bucket with a lid, I started with a 5 gallon eventually moved to a 2 gallon for but any kind with a tight fitting lid will do.
  2. D-limonene (this is an essential oil extracted from orange peels) you only need a few ounces per LB of EPS. so a little goes a long way, although more solvent melts the foam faster, but then you have more solvent to remove later.
  3. EPS (Expanded Polystyrene) foam. you can use just about any 'styrofoam' except the starch peanuts. the color of your end product may depend on the grade and color of your starting foam.
  4. a junkable spoon or spatula.
  5. muffin tins, or shallow silicone drying pans.
  6. molds (steel or silicone )
  7. Toaster oven, or possibly even an old ezbake oven or dehydrator may work, (only needs about 200F-250F, possible to do this with an oven or other heat sources.) not very smelly, but i use toaster oven on a back porch
  8. some spare cookie sheets or even some waxed paper or whatnot to leave things to finish curing on.

BTW thi was my source for the-D-limonene although you can get it through amazon and possibly some janitorial supply houses as its sold as a food additive and safe kitchen cleaner. link to ebay seller of good quality 99% pure limonene i used. (not connected to seller in any way other than as a satisfied customer)

Step 2: Getting Started

'Melting' the EPS, starts with breaking it up into chunks that you can put into your bucket, and then simply adding a few ounces of D-limonene solvent to the bucket and then start feeding EPS into it and let it dissolve in the process the gasses in the foam will bubble out. and the Polystyrene will turn into a runny goo when it touches the solvent. you can keep stirring it in to speed things up, or you can just toss it in and snap the lid on and wait for it to all melt. (EPS floats, so it will only touch the solvent on the bottom, ideally you want to use as little solvent as needed to get the job done, i usually added about 20 cc's of limonene per 4 cubic feet or so of EPS.

In the long run, I think i plan to go back to the 5 gallon hardware store plastic (PP) bucket with a tight fitting lid, and just keep adding EPS and solvent and pulling out liquified polystyrene/solvent from time to time. rather than doing batches emptying the whole bucket as i did during a lot of my experiments. If everyone just did this step, and digested down all the packing styrofoam they get we could save a bunch of landfill space.

Please note, if you want to work with a colored end product, its pretty easy at this step to add some other #6 PS objects such as a Red Solo cup, or colored disposable plastic picnic plate or whatnot. its amazing how much dye is in some of those! the blue in the above photos was from Insulation foam thich started out light blue, but went dark blue as it melted and lost all the air bubbles..

Step 3: Evaporating Off and Thickening the Maker Goo!

Once the air has all bubbled out of your solvent/eps bucket. you should have a pretty clear goo (if using white polystyrene) next step is to spoon out some of it into some sort of wide flat drying dish. ( started using a silicone "twinkie" baker mold to pour/spoon off 4 oz chunks of the sticky liquid and i then let it evaporate for a few weeks on my back porch shelf. this helps it thicken enough to be removable and handleable although after 2 weeks the solvent is enough to still feel squishy like a gummy bear, it can be demolded from the drying pan, and flipped over to allow for better drying.

The slow drying time is a disadvantage of the Limonene, but it being nontoxic, biodegradable, renewable, and pleasantly citrus scented, are a good trade off for the slow thickening time.

Because of the slow drying time, its handy to do largeish batches, because once they are dried to this state, you can cut them up into smaller chunks or leave them for use

Step 4: Casting!

Once you have some ingots of PS and limonene that have dried enough to be thick gummy bear consistency, its easy to tear it apart of cut it with scissors for cutting it into bits to fill molds with. Steel molds you can add a little furniture wax or oil to the mold to keep it from sticking, Silicone molds need no release.

cut off chunks and pile them on the things you want it to flow into, and then drop it in your toaster oven, set to 210F the solvent helps lower the melting point of the plastic down from the 250F-300F pure polystyrene, and bake it at 210F for about 30-45 min if there are any bubbles, you can gently pat the surface with a spatula or other poker to get them to pop. (fewer bubbles in more thick/dry stock)

if the mold is overflowing you can pinch off some of the excess and then toastsome more it so that the rest runs down into the mold.

when done remove them from the heat, depending on how flexible/solventfull the starting material is, you may be able to demold it right away once it cooled, but it may be squishy still. you can either leave it to try more, or you can freeze it mold and all and the parts will temporary harden and shrink a little making it easier to de-mold

In the future i want to experiment more with casting LED's into them, as well as adding magnets, trying out some plasticisers such as Butylated rubber particles to make it a more HIPS style plastic. im also wanting to try it out with a small desktop injection molding rig too.

Step 5: Fin! Notes and Links.

This is only a simple starting point guide, most of the molds i made were mostly just proof of concept, I was preparing for the 7th Annual Albuquerque Mini Maker Faire, where i showed off my Styrofoam re-creations and a bunch of my experiments that lead me up to this point, (in the process i tried a lot of other solvents, xylene, toluene, acetone, gasoline, naphtha, lacquer thinner, M.E.K.) lots of them melt it, but all are less pleasant to work with than D-limonene and in some cases such as acetone, my end results were super bubbly, Note: although its possible to get PS to fall out of acetone solution by adding water. (which may be useful for some resuses)

below are some of my more random notes and links i found during my research.

Here is a instructable about using just acetone i think i ran into early on in my research, and is totally worth a credit.

About Solvents:

Why so many organic solvents are bad for you..

Acetone: Works great, turns it into a slurry of dissolved polystyrene that will eventually evaporate thicken and then finally harden, most of the gas is lost, but the acetone gets trapped eventually and blows bubbles into the slowly solidifying stuff, making it bubbly and less than ideal to cast with. Interesting note, water makes the eps crash out of the acetone, but make a odd milky slushy eggdrop soup like stuff. I've not really worked with water crashed out eps much yet, did it two times and all, may try baking it after drying it to see if it will melt back into a puck.

Xyline: also dissolves the product fast, but takes a good long time to dry, and is stinky and bad for many reasons.

M.E.K.: (methyl ethyl ketone) also dissolves the product fast, ends up with a fairly bubble free end result, but is also stinky, and bad for many reasons.

Lacquer thinner: slow, does soften it and degasify it, but not fully dissolve it, and is stinky and bad for many reasons. End result foams and puffs up as it dries. And dries white, one neat thing is its totally not sticky. And i don't think much of any is being pulled along in the solvent, making it possibly the most solvent friendly. Might be good for just strictly commercial use, this may also vary by formulation

D-limonene: works great on plain white ps, will dissolve quite a lot per oz, nice smell, not known to be toxic, leaves the ps very clear (sometimes a slight yellowing) virtually no bubbles, long glass transition. (verrrrry long transition, can take months to feel like thick rubber. And stay that way at elevated heat (80F and plenty of circulation for months.) when solid, re melts at about 104C/220F(seriously this is like easy bake kids oven temperatures! and flows nicely. Casts with relatively few bubbles* Cons, very long dry time. And relatively expensive Pros, not known to be toxic, nice smell, good clean results, not much shrinkage, re-meltable and flows well, stays glassy

Toluline: works much like limonene stinkier but faster has many more health risks. and bad for many reasons.

Gasoline: works but dirty, very yellow stinky foamy result in the end... and is stinky and bad for many reasons.

White gas/ Naphthalene: works to degas and shrink it to some degree but does not soften or melt the EPS.

Links: misc.

Experiments in mixes of acetone and D'Limonene
Cool tool! Looks like 87% d-limonene to 13% Acetone by volume should do the best melt. According to the above site. Theoretical mix RA of 3.8 (lower= better)

But 25% d'limonene to 75% M.E.K has a theoretical RA of 3.7

Or 21% Xyline to 79% acetone gets us down to ra of 3.2 which is the best i've pulled from the above table. Sofar. Other experiment notes and links:

Tried this mix, using a 50ml test tube filled it with 43ml acetone and about 7ml limonene, and absorbed EPS until it stopped accepting more. Let it tsit 30 min, and then mixed in 45ml of distilled water and mixed. Milky thick eps crashed out of the slurry and the acetone was absorbed into the water. kicking out about 55ml of liquid although im estimating since i spilled some, wound up with a slightly milky 50 ml of liquid, im letting see if any settles, ideally in the future id love to try and absorb the water out, (perhaps with water beads? Can't recall if they dissolve in acetone/limonene,) or distil off and recover the acetone, and see if we can do it again. I have also not investigated only using acetone vapors, perhaps a bucket with a pie tin in it with acetone under it, and ps, and a lid. Or eventually a condensing chamber i can pipe in ther hot distilled acetone? The end result was a sticky ball of wet ps. It’s self sticky and very thick, but it is handleable, (standard disclaimers for solvents on skin, gloves are not a great solution, because the stuff sticks more to them than skin) and shapes like putty, i kneaded it a bit to get out the water/acetone, and proceeded to leave one blob to dry, and one blob mushed into a small mold and i will see how it dries. Im suspecting this version will still contain a fair amount of solvent, and may still take some time to dry End result was fairly white and milky with teeny bubbles, workable. Should be able to distil out the acetone from the water for reuse.

Limonene sadly is not water absorbable so not sure how mixes of acetone/limonene will work, and results of drying lomonine under water have lead to very milky results and super slow drying time.

Polysevert uses Cymene to do what im doing with limonene info on the solvent here.

more on Cymene (thyme/Lavender terpene)

We examined the dissolution of polystyrene into p-cymene and related substances to develop an alternative method for the recycling of expanded polystyrene. The dissolving power of p-cymene [212.0 g (100 g solvent)−1] to polystyrene at 50°C compared favorably with those of 2-p-cymenol [156.7 g (100 g solvent)−1], (R)-limonene and its structural isomers [181.7–197.1 g (100 g solvent)−1], and Abies leaf oil [84.7 g (100 g solvent)−1]. The favorable solubility of polystyrene into p-cymene can be explained by the solubility parameter. p-Cymene and polystyrene can be recovered almost quantitatively from the polystyrene solution by simple steam distillation.

Carrier, a term for something like a solvent, may be what im needing for the end reprocessing, folks are suggesting toluline, but, in the process im hearing about making conductive ps mixes, using toluene as the carrier,

Related links

My ebay source for 99% pure clear d-limonene


My Youtube Growing playlist of plastic recycling links mostly EPS but some PET, some PP and others…

For more information or questions email

adric@quelab dot net Or tweet @killbox

Step 6: Continuing Saga, New Bucket Technique and Trying Out Lavender Oil

In the last year i have experimented with some more techniques.

One has been working with mixed/dirty polystyrene/eps including drink cups, and paper plates, and togo boxes. (lightly rinsed but not super clean)

I also found that if you use a 5 gallon bucket or larger you can put about a gallon of water in first, and all the Limonene floats, as does the polystyrene. this not only allows the eps to sink a bit deeper into the limonene, decreasing the solvent needed, but also the water gives food particles and other contaminants a place to settle out into, this plus the layer of limonene/polystyrene on top keeps it from smelling, and the end result eps is a little more easy to get out of the bucket because its a rubbery layer on top of the water.

One caveat to the water on the bottom tecnique is that its easy to trap some water in the removed eps/solvent goop. ive mostly fixed this by transfering it from the bucket into a cookie sheet and letting it dry out flat until i can flip it.


I have also begun some experiments with Lavender Essential Oils. i have found its just about as good at dissolving polystyrene, and may evaporate a little more quickly but for the most part its more expensive. (unless i can buy some expired or perhaps cheaper grade of the stuff since i'm not using it for perfume or food use. it does also have the advantage of the fact it can be steam extracted from lavender and lavender will grow here whereas i cant grow much citrus for d-limonene. Still some room to experiment on the whole process with this.

One other thing that keeps me from doing a larger scale trial with lavender essential oils. is the fact i have at least one friend who is allergic to lavender and id hate for my project to cause them extra stress if they were to stop by.

Trash to Treasure

Participated in the
Trash to Treasure