Plastic milk

Can you make plastic out of milk and vinegar?

You would imagine that you’d need some pretty noxious, smelly chemicals to make plastic, but you can actually find the things you need to make malleable, doughy pieces of material in your own home. Instead of putting vinegar on your fish and chips and wasting your milk in your tea, use the two liquids to become a polymer chemist…

What do I need?

- a pint of milk

- a saucepan

- a sieve

- a spoon for stirring

- 20 ml of white vinegar

- rubber gloves

- water

What do I do? Pour the milk into the pan and gently warm it. When the milk is simmering (don’t let it boil) stir in the white vinegar until you notice whitish-yellow rubbery lumps beginning to curdle in the mixture at the same time as the liquid clears. Turn off the heat and let the pan cool.

What will I see? First of all you’ll smell the vinegary reaction, which is the key to this process at work. As the vinegar is added and stirred, the liquid gets clearer and the yellowy rubbery lumps form. When the pan has cooled you can sieve the lumps from the liquid, tipping the liquid down the sink. Put on the rubber gloves and wash the lumps in water. You can then press them together into one big blob – they will be squishy and will feel as if they are going to fall apart, but they will stick together after some firm kneading. You can now use your artistic skills to fashion the material into the shapes of your choice – New Scientist staff came up with balls, stars, a heart-shape for a pendant and even dinosaur footprints. Leave the material to dry for a day or two and it will be hard and plastic enough to paint and varnish.

What’s going on? You have used the combination of an acid - in this case vinegar, which contains acetic acid - and heat to precipitate casein (a protein) from the milk. Casein is not soluble in an acid environment and so, when the vinegar is added, it appears in the form of globular plastic-like lumps. Casein behaves like the plastics that we see in so many objects around us, such as computer keyboards or phones, because it has a similar molecular form. The plastics in everyday objects are based on long-chain molecules called polymers. These are of high molecular weight and get their strength from the way their billions of interwoven criss-crossing molecules tangle together.

PS: Some forms of cheese-making rely on a similar technique – the name casein comes from caseus, the Latin for cheese. The Indian cheese known as paneer is made in a very similar way to the plastic you have just made, although in this case lemon juice is the acid used rather than vinegar. Afterwards, unlike our plastic milk, it is not dried out and allowed to harden to tooth-breaking consistency, and so remains soft and edible.

For more experiments go to www.newscientist.com/hamster

Explore Books

• Book Extracts

• Book Reviews

• Books Group

• Audio Books

Times Recommends

• Superfreakonomics by Steven D Levitt and Stephen J Dubner
• The Times picks the 50 best paperbacks of 2009
• Vincent van Gogh’s letters show the soul of the artist