Milk is great for your teeth and bones, but did you know that it can also be used to make plastics? Milk-based plastics, or casein plastics, were used in a variety of products, including paint, buttons, knitting needles, pens, and combs up to the mid-20^th century. Recently, interest has renewed in casein plastic as an eco-friendly alternative to less biodegradable products like crude oil plastics, and the best part is that it can be made right at home!

You will need:

• 1 cup of milk
• 4 tsp white vinegar
• Stovetop oven and pan or microwave and microwaveable container
• Mug, bowl, or other heat-resistant container
• Spoon
• Paper towels
• Plate or tray
• Optional: Cookie cutters, glitter, food colouring, paint

Instructions:

1. Heat 1 cup of milk on a stovetop or in the microwave until steaming
2. Put 4 tsp of white vinegar in a mug or bowl and add the hot milk; mix slowly for several seconds
3. Stack several layers of paper towel on top of a plate or tray
4. Once the milk-vinegar mixture has cooled, scoop out the lumps (curds) and place them on the paper towels
5. Folding the paper towels over the curds, press down to release the excess moisture. Use extra towels as needed to soak up all the liquid.
6. Knead the curds together into a ball of dough
7. (Optional) Add food colouring or glitter, or press the dough into a mould to make different shapes
8. Leave your plastic to dry for at least 48 hours
9. (Optional) Once the plastic has dried, it can be painted or glued together to make new shapes

Why does this work? Milk is made up of fats and proteins suspended in water; one of these proteins is called casein. When an acid like vinegar is added, the casein molecules reorganize themselves into a chain called a polymer. So long as they’re warm enough, these polymers can be shaped and moulded together; once they cool down, they stiffen up and turn into hard plastic!