Instructables
This is a quick and simple method for making your own general-purpose plastic. The constituent ingredients are milk and vinegar. That's it. The total cost is less than $10, possibly less than $5 if you can get a good deal.

The plastic is moldable, and has a consistency of soggy cheese (I certainly hope I never encounter cheese that's anything like this!). When all is said and done, it should take you about 10-15 minutes to make the plastic (less if you make a small amount), 10 minutes of cleanup, plus 2+ days to allow the plastic to dry. As always, your milage may vary.

As for the final product's strength and whatnot, I would classify it as "okay." If you roll it thin (as I did in this instructable), it can easily be snapped in half, though it will probably survive a small drop on to carpet. Thicker pieces seem to be more resilient against average abuses - no problem dropping on to carpet, and if it's thick enough, you wouldn't be able to snap it in half. A blow from a hammer or other such object would quickly shatter it, though.

All in all, I would say this is mostly useful for folks looking for a fast and dirt cheap alternative to much better products available to the average joe. It's definitely not for something that will be handled on a daily basis - good enough for light decor, not much else.

This is my first Instructable, so bear with. Constructive criticism is always welcome!
 
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Step 1: Ingredients & Utensils

instructable001.jpg
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This doesn't require anything fancy.

Essential Items:
Milk
Vinegar
Large Pot
Larger Pot (needs to be the same size as the other, or larger).
Spoon, preferably plastic or metal
Strainer or Colander, the finer the better
Stove or other item with which to simmer milk.
Paper Towels, lots and lots of paper towels

Handy, but not necessarily essential, items:
Wax Paper (good for rolling and shaping on. Water and other liquids bead up on it for easy clean-up; also non-stick with the casein)
Aluminum Foil (good for certain types of molds)
Rolling pin (if you're going to make a flat sheet of plastic)

Before you begin making the plastic, it's important to know what you're intending to make. By knowing what you're final goal is, you can make the preparations for the mold before you have a sloppy wad of plastic on your counter.

For this Instructable, I am making a curved piece that will fit on the front bezel of my computer case. Since this is beyond the scope of this particular instructable, I'm going to gloss over what I'm using. My mold is going to be the front bezel of the computer case, covered with aluminum foil. The plastic will dry nicely on top of it, and the aluminum won't shrivel or wrinkle when it gets wet as the plastic cures.

How much milk and vinegar will you need? The basic ratio that I follow is 1 TBSP of vinegar for every cup of milk. (16:1 ratio, milk to vinegar)

1 cup of milk will produce a puck of plastic about 2" in diameter, 1/8" thick.

To cover my case bezel, which is about 6 inches wide and 8 inches tall, I am going to use 8 cups of milk (and therefore 8 Tbsp of vinegar).

Step 2: Heat it up

If you've never heated milk before, it's important to know that if you heat it too fast, it will start to burn on the bottom of the pot. To bring it to a simmer, it's best to keep the heat down to about 50-60%.

I don't follow my own advice, and use full heat, because I don't want to wait.

While the milk is heating, be sure to stir it occasionally, so it doesn't burn. Also, if you're heating more than one or two cups of milk, measure the vinegar out into the cup while the milk is warming. This is personal preference, as it makes it easier to pour the vinegar in all at once, rather than measuring it out in a hurry.

During this time, you may need to pander to a needy cat, if one happens to be around.

When the milk nears boiling, you will notice a foam forming on top of the milk, as well as a little noise coming from the pot. Steam will start to appear too.

Once you reach this point, turn off the heat, pour in the vinegar, and stir. You will immediately notice chunks of casein forming. Stir it for another thirty seconds or so, for good measure.

Step 3: Strain

Slowly pour the heated liquid through the colander and into the larger pot. Most of the chunks of casein will get caught. We pour slowly to avoid splashing the plastic-loaded liquid into the sink. Something tells me that chunks of this stuff in the drain is not a Good Thing(tm).

Once you've poured it out (don't worry about what's left in the bottom, we'll get to that), gently shake the strainer, and swirl it around a little. Most of the casein will lump up in the bottom, pulling itself out of the holes. Make sure a majority of the liquid is strained out, but don't press it out -- the casein will just get stuck in the holes, and make it harder to get out.

Now that it's all clumped together, dump it out on some wax paper.

If you have a super-porous strainer like mine, you may want to pour the liquid through the strainer several times. Doing it a second time pulled a chunk about 1/4 as large as the original mass; that's a nice addition.

Step 4: Sop up the excess

Picture of Sop up the excess
After you've strained all of the casein out of the liquid, you'll want to soak up some of the remaining juice in the mass on the wax paper.

Use a few paper towels, and press gently on the casein. The liquid will spill out like squeezing a sponge. Be careful not to make it too dry, because it will become difficult to mold if it's too dry.

Step 5: Mold!

At this point, you're ready to do whatever you want with the plastic.

It will take about two days to cure, but if you're using a mold where it cannot easily breathe, it will take longer.

One thing to watch out for is that the casein will warp when it's drying, especially if you have it rolled out into a sheet. It's best to put a weight on it. Watch out, though, because it will seep a milky-vinegary scented liquid into whatever is holding it in place. I used a heavy programming book...and it now has a funny smell to it. Awesome.

For my project, I just need to roll the casein out and let it dry.

Lay another sheet of wax paper over the casein. Use a rolling pin to spread it out. If you didn't dry it too much in the previous step, it should roll nicely, without many cracks or chunks.

Finally, I pressed it between two sheets of aluminum foil, and curved it across the bevel I'm using.

Give it a few days to dry, and it'll be ready to go. This is critical. Depending on how you wrap/mold your casein, you may find it takes more than a week to dry. Wrapping mine in foil took two weeks to get remotely dry. As is expected, the thicker it is, the longer it will take to dry.

I should also note that if you're making a flat piece like I am, the plastic will curl if you remove it from its mold before its dry. I made this mistake with this project, and ended up with a piece that was unusable because it curled.

The final product is quite rigid when it's thick (1/8 inch or thicker), moderately pliable when it's a little thinner, and brittle if it's paper thin. It's also sandable and paintable.

Go forth and have homemade plasticy fun!
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deej121 days ago

how is it to heat? can i make a tobacco pipe out of it?

sudanione3 years ago
how can make it transparent

As a colloidal material, protein glues can never be made truly transparent. However, some (like isinglass) approach it, especially in thin pieces. (Isinglass and other gelatine-type glues are not waterproof without denaturation by tannins, bichromate salts, formaldehyde, or the like, though.)

You can't.
sehrgut23 days ago

What you've made is (besides being "cottage cheese") traditional carpenter's glue. If you want to encourage faster curing and decrease shrinkage, you can use fillers such as sawdust (depending on coarseness, will be similar to "wood composite" plastics); chalk or marble dust, gypsum, slaked lime, or slaked plaster (consistency much closer to plastics like bakelite); or even sand (for a more "concrete" texture). Fillers will also decrease the brittleness of the material at the expense of hardness. Plasticisers such as glycerine, honey, or molasses (if you're trying to stay completely "appropriate technology"); or a mid-weight PEG (if you don't mind a bit of modernity) will also let you modify its properties significantly.

decat21 month ago

what you just made is 'home made cottage cheese', farmer's cheese, paneer,, whatever the local people would call it ... exactly the same recipe up until when you dried it or ironed it. Same exact recipe all farm mothers made for years before they had stores to buy it from... ;) I still make it, and eat it...sometimes I add some cream to cream it and some salt or spices for more taste... I suppose you can dry it and it would be kinda plasitcky... I would add some fungicide to it so it wouldn't mold though. :)

enelson811 months ago
What is the approximate density of this plastic? D=M/V
Does it stink? and could it be made to replace plastic pellet gun pieces, if the previous were plastic too?
skooterv25 years ago
I play airsoft a lot and I play with some people with guns that hurt pretty bad...and this may sound weird but I was wondering if I made this thick enough do U think it could withstand some pretty hard blows like from guns shooting at 400+ fps... TYVM
btw is there anything I could add to make it stronger?? And if u could e-mail me back on this I would greatly appreciate it
cd41 skooterv25 years ago
well this maybe the dumbest thing i ever suggested but you could try putting pencil lead(graphite) in it it is carbon and they add carbon to steel to make it harder and fabric or something but thats just what i would try
tbh-1138 cd411 year ago
Steel is iron alloyed with carbon. Putting pencil lead in casein would be like putting pieces of steel in lead to make it harder. It won't be much better than it would without the graphite. Something like fabric or paper pulp could work, though, and I don't think it would set any faster. Fibers make things stronger.
Cool Idea, But how much milk are you willing to spend on this?

Imagine, an army of Cheese-weilding warriors!
Use the Cornstarch, water, and oil plastic its hard and not too brittle
http://www.instructables.com/id/Easy_Biodegradable_Plastic/
make a thin sheet then cover the back with glue and fabric
Coffeebot (author)  skooterv25 years ago
It might work, if you make it thick enough. It's pretty brittle in thinner layers, and as such, wouldn't do well as body armor.

As for "making it stronger" (your note below), you could possibly add some fabric, of some sort to strengthen it.
Thank you.I really appreciate u getting back to me so quickly. How would u suggest adding fabric to it? Like just adding it in randomly when molding or what? Sorry I have no idea about that. Thanks again
Coffeebot (author)  skooterv25 years ago
Not "randomly" but yes, while you mold it. Probably sandwiching the fabric between two layers of casein would work You'll need something fairly porous -- much looser than cheesecloth, I think. The reason is because of the thick, chunky consistency of the casein, you'll need a lot of gaps between threads in order for two sides to join together.
sorry another question if u don't mind. The juice that drains out of the casein and into a large pot, can u stir it and make that into plastic, too?
thank you And one last question if u don't mind. How thick would you recommend making it? Obviously you have more experience with casein then me. Tyvm again.
fretted1 year ago
Make Your Own Casein Glue from Milk
1. Heat some skimmed milk (do not let it boil)
2. Add about 3 teaspoons of vinegar (an acid) to the milk and stir slowly until the milk
separates into curds (solid sticky bits) and whey (clear liquid)
3. Pour the curds and whey through a tea strainer or sieve to collect the curds
4. In a container, add a little bit of bicarbonate of soda or milk of magnesia (alkali)
5. You should now have a sticky white substance called casein (milk protein). This can
be used as a binder in paint – just add some pigment!
What you've made right there is what we in India call 'paneer' we use it in curries n stuff its delicious, its a kind of cheese, and i'm not sure its a plastic.
You are right that what he has made is Paneer. (Here in the states it is called Cottage Cheese.) However, do a google search for Casein Plastic and you will find that it was a widely used plastic for making buttons, knitting needles, ink pen cases etc. in the early 20th century. It is a polymer by definition and therefore technically a plastic. When used in manufacturing, it would be treated with formalin to retard an bio-degradation. Casein was also a widely used medium for paint.
fqian yan2 years ago
will mold grow on it in the process of drying?
billraymond2 years ago
Are you sure this is truly casein?? My understanding is that casein is precipitated from milk by rennet, not heat. Heating whey with vinegar or other acidifier creates ricotta, which is not a cheese, as it contains no casein, but is rather the precipitated albumin and other (not casein) proteins. Galalith is made from casein and must be fixed in a formaldehyde bath; it is not moldable.
CamoBedding2 years ago
I had no idea you could make home made plastic.
Is the Formaldehyde + Milk Galalith plastic brittle? can it keep a sharp point? will it bend? i will definitely experiment with casien

Any other chemistry suggestions would be welcome.
I want to use casien to make a DIY arrowpoint. I fear that Casien plastic will be

far, far too brittle. is this true?
wow very interesting.
It is very interesting to make plastic out of milk.
But what are the advantages of extracted plastic?????
Although it contains caesin, would it cause any harm if someone eats it??????
Please do reply as soon as possible......
This is cheese. Period. Fromage. Queso. Formaggio. Cheese.
Ah-yup. And while it is plastic by nature, a much superior plastic (harder, more resilient to shock, more resistant to mold) can be made by "dissolving" styrofoam in acetone.
bpfh Broom3 years ago
This is relevant to my interests. Please explain more :)

Just dissolve the styrofoam (polystyrene?) in acetone to a thick goo, mold and leave to dry in a remote area as not to get her indoors all worked up about the acetone smell?
Broom bpfh3 years ago
Pretty much, bpfh. It's a weird, fun process: the acetone "eats" up the styrofoam like a hungry monster, turning a huge amount into a small "sediment" of sticky plastic.

It can take days & days for it to dry on its own, and of course it gives off acetone fumes the whole time. There's no chemical reaction - the acetone just dissolves the styrene in the the mostly-air styrofoam (emphasis on "foam"!), and then gets trapped inside the drying skin of the finished plastic if it's thick, slowing down the drying.

It shrinks somewhat in the drying process, but never (IME) breaks. Also, it seems to change if left in the acetone for a long time, becoming resistant to shape change, so it's best to mold it immediately after dissolving the styrene.
Broom Broom3 years ago
BTW, an entire styrofoam cooler can be dissolved into about a pint of styrene, if you want an idea of how much contraction goes on in the "eating" portion! Don't have any stats on the drying shrinkage, but it's more like 1-15%... something reasonable.
bpfh Broom3 years ago
Thanks for this update! I may try this in the next few weeks!

My project is quite simple: I have a motorbike where you cannot really get any plastic parts for it anywhere for love or money, and I need new wingmirror shells.

So either you are very very very lottery jackpot winning lucky if you find a part on ebay, or you cast it yourself.... I was originally thinking about resin casting, but resin costs a fortune. Casein seemed a good idea but being organic , I'm not sure about resistance to mold and fungus, and styrene seems easy enough to make... even if it may be more fragile than standard ABS plastic, I'm not very worried. You just need a ton of styrofoam to get a handful of goo :)

The other alternatives, like Sugru cost too much to be cost effective, and low temperature thermoplastics could melt if being left in the sun too long, so this method could allow me to make my prototype mirrors !

Cheers,
Daniel

lycoris36 years ago
I just told my dad about this and he said you were basicly making cheese! He's a chief.
Mr. Coffeebot... we have a project in Chemistry... can you give me a tip because we choose this as our project... ty!
use formaldehyde; add it to the curds
bpfh beehard443 years ago
LOOOOOOOOOOOOOOOL :)

Darn right. It gives it a little more "bite"! (it will also slow down growth of green fur :) )
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