Make plastic from milk? It seems like some sort of lactose intolerant horror story, but it’s actually a really cool science process. Create your own toys, beads, jewelry, and more, with ingredients you have right now in your kitchen. It’s so easy and super cool!
Turn Milk Into Plastic Toys!
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Also known as casein plastic, this process has been used for over 100 years and is the way they used to make plastics before 1945 when synthetic plastics were introduced. Even royalty wore jewelry made from milk plastic many years ago. How cool is that?
With this simple process you can make toys, beads, jewelry, decorative pieces and more. This is a great, budget friendly experiment, with spectacular results that will have your students pumped with excitement for science!
Milk Plastic Supplies
A stove top or microwave to warm the milk
Milk (we used 2%, lower fat content is better)
White Vinegar or Lemon Juice
Bowl
Spoon
Strainer (or can create your own using cheese cloth or similar)
Paper towel
Molds (we loved using our Lego minifigures and Dinosaur molds) or other tools for shaping.
Time: 30 to 90 minutes for the experiment, then 2 days for drying. Add in a little extra time for painting once dry!
How To Turn Milk Into Plastic
Measure out 1 cup of milk (you can also use chocolate milk and the end result smells amazing!), this makes about 4 minifigures or 4 dinosaurs. Heat on the stove top in a pot or in the microwave in a heat resistant bowl. You want it to just start steaming. Remove from the heat. Add 4 tsp of vinegar or lemon juice and stir gently.
The amount of vinegar is not exact. We used 4 tbsp by accident and it was fine, just made for a more intense vinegar smell!
You will notice that it immediately begins to curdle. You’re making curds and whey!
Stir gently for approximately one minute for the full reaction to finish and all the curds to form. Don’t stir aggressively. Be gentle.
Strain off the whey using a strainer or you can use cheese cloth (or similar). Let drip for a few minutes until most of the liquid has drained off. Gently smoosh the curds around in the strainer if needed.
Now remove the curds and place them on a few layers of paper towel. Carefully pat and squish to remove more liquid. You may need to replace the paper towel and repeat a few times. The goal is to remove as much liquid as possible.
You will notice it is kind of crumbly and squishy, but you can smoosh and shape it.
An Extra Optional Step In The Name of Science
Now you can put it in your molds at this point but we discovered that if you put the curds in a jar or bowl, soaking in vinegar for an hour, you will get a much smoother final product. Plus they are more white if you do this extra step. If you do the extra vinegar soak, once the hour is up, repeat the straining, and paper towel drying process again. This time you will notice it is smoother in texture and no longer crumbly.
How To Colour Your Plastic Milk
During the vinegar soak you can add some food colouring if you want. Just put a few drops in with the vinegar while it is soaking and it will colour the curds. Or make yours glow in the dark with our favourite trick!
Final Steps For Finishing Milk Plastic
Now squish it into your molds. We used silicone molds to make Lego minifigs and dinosaurs.
You can also shape it by hand. Roll it to create beads, then use a skewer to put a hole through it before setting it aside to dry. Or flatten it and use some cookie cutters.
The drying process takes time, approximately 2 days depending on your natural humidity levels and how much moisture you removed with the paper towels. But you can remove it from the silicone molds after 24 hours and this will help speed up the drying time.
Once dry, clean up the edges a bit if necessary, just like you would with any other casting. You can do this with just your fingers, a piece of sand paper or other tools. It will be hard plastic now, so it might take a little extra work!
You can paint the final products with either acrylic paints or markers. I used acrylic paints and a sharpie for the faces on mine. Spray them with a clear coat to give them a nice shine once you are finished.
VOILA! Who knew it was so easy, and so much fun, to make plastic from milk!
How Long Will Milk Plastic Last?
Our oldest Milk Plastic Toys are over 2 years old now and show no signs of degrading. We haven’t done any experiments yet to see if they might break down with moisture, or heat, or sun, but that might go on the books for a future study. They are definitely highly durable!
The Chemistry of How Milk Turns Into Plastic
This is a chemistry experiment working with polymers. Polymers are molecules that have formed a regular chain structure. Milk contains molecules of a protein called Casein. During this reaction between warm milk and acid the casein molecules unfold and form long chains called a polymer. The polymer can be molded and shaped which makes it a plastic. In this case it’s called casein plastic or milk plastic because of the type of molecules that created the plastic.
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Emma says
Wow, this sounds so neat! I had no idea you could make plastic from milk!
Mark says
Is making plastic really that easy? I mean, is it really? Not that I think it’s impossible it’s just that I’ve never thought it can be made of food of all things.
Shelley says
Yup! Up until 1945 this is how plastic was made. 🙂 To make it extra hard like they did back then you need to do a formaldehyde soak, for obvious reasons we skipped that step and they are still plenty hard.
Sarah @ Share it! Science says
Such a fun experiment! Just think if we still made plastic this way…the long term effects on the landfill probably wouldn’t be so dire! Thanks for the great post.
swapna says
This is interesting! Would love to see your posts in the Practical Mondays Link Up:)
Mother of 3 says
I had NO idea you could make plastic from milk! We’re going to have to try this!
Sheila says
This is basically the recipe for Farmer’s Cheese — you just stop at the “crumbly and squishy” stage and eat it, or refrigerate it for later. So, lunch, science lesson, and a craft, all in one!
Andrea says
We tried this and it worked great, until we did the extra vinegar soak. That made it SUPER crumbly and dried out. It wasn’t moldable at all 🙁 We tried again and skipped that step and it came out great. I wonder if it had to do with the acidity in the vinegar?
Shelley says
The final product is not moldable. It is quite crumbly if you have done it properly and removed as much liquid as possible. That is why you need to use a mold and pack it into the mold and then let it dry. The mold is what gives it the shape once it dries and hardens. If you are looking for a product to mold I would look for air dry clay. Best of luck.
Brooklyn Castro says
Hi, we had the same result as the poster above- we did the extra hour vinegar soak, and the result was a less smooth, pile of crumbles. We did use the crumbles and press them into our molds, we will see what happens. However, in your instructions it states quite clearly that after the extra vinegar soak, it will be “smoother in texture and no longer crumbly”. You also indicate that you could just roll this into beads or shapes, but we could not get the crumbles to stick together at all. A fun project, curious to see if the molds will turn out, but a bit confused about your original instructions versus your response to another poster that it should, in fact, be crumbly? Thank you!
STEAM Powered Family says
If you are running into issues I would try a different fat content milk. Yes, it gets crumbly if you remove all the liquid, but the extra vinegar soak does make a difference in the smoothness and whiteness of the final product. It could also be a difference in the type of vinegar you are using. The best advice is to experiment! It’s science, test and retest, and see how your results change. 🙂 We’ve made these many, many times and never had any issues. Happy experimenting!
PS. I’ve edited this article to include links to some of our other milk plastic projects!
Brooklyn Castro says
Thank you for the response! These did not turn out- they came out like crumbles stuck together, and smell really strongly of vinegar still- so we will try, try again! Thank you again!
STEAM Powered Family says
Definitely try again. I was thinking about it after and I also wonder if type of milk makes a big difference. For instance if you live in the USA, perhaps your milk has a different composition than milk in other countries (due to breeds of cows, what they eat, processing of the milk, etc.), which may give a different result. I do have lots of readers around the world that have successfully made milk plastic. So definitely worth experimenting and trying again. 🙂
Emily says
I’m wondering if you can do anything with the milk/vinegar mix that’s left over from the straining? Can you use it to make more things or is it throw away?
Shelley says
With this experiment you are creating curds and whey. The curds become your plastic. The liquid is the whey. Perhaps you can find something to use the whey for. 🙂