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National Museum of Nuclear Science & History

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Milk to Plastic!

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. With this easy Project you can make toys, beads, jewelry, decorative pieces and more. This is a great, budget friendly experiment, with spectacular results.
Milk Plastic Supplies
• A stove top or microwave to warm the milk
• Milk
• White Vinegar or Lemon Juice
• Bowl
• Spoon
• Strainer (or can create your own using cheese cloth or similar)
• Paper towel
• 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!

Steps:
1. Measure out 1 cup of milk.
2. Heat on the stove top in a pot or in the microwave in a heat resistant bowl. You want it to just start steaming.
3. Remove from the heat.
4. Add 4 tsp of vinegar
5. Stir gently for approximately one minute for the full reaction to finish and all the curds to form.
6. 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 “Squeeesh”(scientifical term) the curds around in the strainer if needed.
7. 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.
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.
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.

More 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.



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