Turning Milk Into Plastic

Did you know plastic can be made from milk? That’s right, it definitely can, and it’s an experiment that’s a common part of science incursions for schools! The history of milk plastics spans back hundreds of years, and it’s still in use today. In fact, some plastic makers are even looking into milk-based plastics as a biodegradable alternative to other types of plastic in use across the world.

The best part is that turning milk into plastic is an experiment that’s child-friendly and easy to do at home. In this article we’ll cover how you can turn milk into plastic with just a few easy steps!

The Materials

There are only a few ingredients involved with turning milk into plastic. The chemical reaction at the heart of this experiment happens quickly, and the whole process can be done in under an hour. 

You can turn milk into plastic with just a few basic things:

  • 1 cup of milk
  • 4 tsp of white vinegar
  • A heat safe mug or bowl
  • A microwave safe container
  • Paper towels
  • Mixing spoon
  • Food colouring and other decorations

Each cup of milk makes enough plastic for one or two kids.

The Experiment

The only equipment you need for this experiment is a stove or microwave to heat the milk. If you’re performing this experiment in a classroom then the milk can also be heated beforehand and kept in an insulated container until you’re ready to use it.

  1. Heat up the milk using a microwave or stove. You want the milk to be hot enough that it could be used to make a drink like cocoa, but not so hot that it’s boiling. In the microwave it should take about 60 seconds on full power.
  2. Add your vinegar to a heat safe mug or bowl. Pour the heated milk over the top of the vinegar. As the two liquids mix the curds should begin to separate from the milk. Use a spoon to gently stir the mixture for a few seconds to speed up the reaction.
  3. Using your spoon, separate the curds from the liquid. Spoon the curds out onto a few sheets of paper towel to absorb any excess moisture. Try to leave as much of the liquid in the cup as possible.
  4. Use your paper towels to dry the curds and remove as much liquid as you can. It’s a good idea to wait for the curds to cool slightly before trying to handle them!
  5. It’s time to knead your curds once they’re dry and cool. Simply knead the curds like you would with bread dough. This process helps the curds come together into a ball that can be shaped later on. At this stage your plastic should look a little lumpy.
  6. You now get to decorate your plastic! This is a great experiment for kids and students because they can use things like food colouring, cookie cutters and glitter to decorate their plastic.
  7. Leave your plastic creation to dry for 48 hours. During this time the curds will harden into a biodegradable plastic!

Why the Experiment Works

Turning milk into plastic is a popular experiment at incursions for schools. It’s also a good opportunity to talk to students about plastics and discuss one of the world’s most important and influential inventions!

To understand why milk can be turned into plastic, we need to think about what plastics are. The trouble here is that plastics come in thousands of different variations. They all look, feel and behave differently, so most people aren’t really sure what plastic is. The answer is surprisingly simple: the thing all plastics have in common is their molecular structure. The molecular structure of plastics is known as a Polymer. A polymer is simply a chain of molecules that have the ability to chemically bond with one another. These types of molecules (known as Monomers) can join together and form polymer chains that are much stronger than the original molecules. If enough molecules join together into a polymer chain then you’ll end up with a lump of plastic.

This experiment works because milk contains a protein called casein. When an acid (like vinegar) is added to hot milk, the pH of the milke decreases and the casein molecules begin to unfold into monomers. These molecules then begin to join together into a polymer chain, turning your lump of curds into plastic!