How to Turn Milk into Plastic!

Project Overview: Did you know that you can make solid plastic using nothing but vinegar and milk? This project lets you create your own moldable "milk plastic" which is called casein plastic! It is a great hands-on opportunity to see how heat and acid can permanently change the structure of a protein. WARNING: Have an adult help with heating the milk on the stove, since it will be hot enough to burn yourself!

Materials:

1. 2 Cups of Milk (use whole milk for best results)

2. 4 Tablespoons of White Vinegar

3. 1 Small Pot

4. A Stove or Microwave

5. A Strainer or Cheesecloth

6. A Bowl

7. Paper Towels

8. Cookie Cutters or Molds (optional)

Instructions:

1. Ask help from an adult to heat the 2 cups of milk in the small pot over the stove or in the microwave until it's steaming hot but not boiling

2. Slowly pour in the 4 tablespoons of vinegar while stirring the milk

3. Watch as small, rubbery white clumps/curds begin to separate from the liquid (whey)

4. Keep stirring for about a minute until no more clumps seem to be forming

5. Carefully pour the mixture through the strainer or cheesecloth over a bowl to catch the solid clumps

6. Press the clumps gently with paper towels to soak up as much extra liquid as possible

7. While the mixture is still warm and soft, knead it like dough and press it into cookie cutters or shape it with your hands

8. Set your shapes on a paper towel and let them air-dry for 2-3 days until they harden into solid plastic

Explanation: You might be wondering as to what made the milk turn into plastic when it was mixed with vinegar. The answer is a protein found in milk called casein! Casein normally floats around in tiny, tangled-up balls through the milk without clumping together since all of the proteins have the same charge. Therefore, they repel each other and float through the milk, making it smooth. However, when vinegar is added, its acid contains a positive charge. Since a new charge is introduced, the proteins no longer repel each other: they attract. Therefore, they stick together and form clumps, or curds, no longer having the smooth texture it had before. This process is called denaturization, and this happens within minutes! However, in order for the casein to solidify, or become fully solid, all of the moisture in it must evaporate, and this process can take 2-3 days, which is why you must wait for it to solidify!