Can You Turn Milk into Plastic? Let's Experiment and Try!
Shared by: UT San Antonio Society of Women Engineers
Explore hands-on science activities you can build with things you have around the house.
Recommended Grades: 6th, 7th, 8th
Before beginning, answer the following:
- Do you think that milk can be used to create plastic? Why or why not?
- What do you think will happen when hot milk and vinegar are mixed?
- Measuring cup (1)
- Cow's Milk (1 cup)
- Microwave and microwaveable container (1)
- Thermos or insulated container big enough to hold all the hot milk
- White vinegar (4 teaspoons)
- Paper towels
- Food coloring
- Cookie cutters
- Heat 1 cup of milk in a pan or stovetop until the milk is steaming. Alternatively, you can microwave the milk in a microwaveable container by warming it at 50% power for 5 minutes. It should be about the same temperature as you would want the milk to be for making hot cocoa. Heat for more time if needed.
- If you cannot do the rest of the activity right away, store the hot milk in a thermos until it is needed.
- Add 4 teaspoons (tsp.) of white vinegar to a mug or other heat-resistant cup.
- Add 1 cup of hot milk to the mug. You should see the milk form white clumps (curds)
- Why do you think the milk forms curds when it is added to the vinegar? What do you think they are made of?
- Mix the mug slowly with a spoon for a few seconds.
- What happens when the milk and vinegar are mixed together? Why do you think this is?
- Stack four layers of paper towels on a hard surface that is safe to get damp.
- Once the milk and vinegar mixture has cooled a bit, use a spoon to scoop out the curds. You can do this by tilting the spoon against the inside of the mug to let the excess liquid drain out while retaining the curds in the spoon. Collect as many curds as you can in this way and put them on top of the paper towel stack.
- Fold the edges of the paper towel stack over the curds, and press down on them to absorb excess liquid from the curds. Use extra paper towels if needed to soak up the rest of the extra liquid.
- Knead all of the curds together in a ball of dough. This is the casein plastic!
- How do the kneaded curds feel and look in comparison to the original curds?
- If you want to make the casein plastic into something, you can color, shape, or mold it now (within an hour of making the plastic dough) and leave it to dry on paper towels for at least 48 hours. Once it has dried, the casein plastic will be hard.
For more instructions and a demonstration video, head to the Activity Video tab.
When you added the hot milk to the vinegar, small, white chunks should have become visible in the mixture. This is because adding an acid, such as vinegar, to the milk changes the milk's pH and makes the casein molecules unfold and reorganize into a long chain, curdling the milk. The white chunks are curds. You should have been able to use a spoon to separate the curds from most of the liquid. Additional drying of the curds with the paper towels should have made the curds ready to knead into a ball and use as casein plastic, which can be molded and decorated.
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