There is too much plastic in the world and it is polluting our oceans. What we need is biodegradable plastic. This is plastic that rots away and doesn’t stick around for hundreds of years. Scientists are working hard to make plastics like these. The one shown here is a very simple plastic that will biodegrade – it’s not strong enough to wrap up food, but you can stretch and mould it.

You will need

  • 2 tablespoons cornstarch (cornflour)
  • 3 tablespoons water
  • ½ teaspoon cooking oil
  • Food colouring (optional)
  • Microwave-safe bowl and a microwave
  • Tablespoon
  • Teaspoon
  • Mixing spoon
  • Oven mitts (gloves)
  • Cookie cutters (optional)

1 Mix the cornstarch, water, and cooking oil in the bowl to make a milky-looking liquid. Add a little food colouring if you would like coloured plastic.

2 Ask an adult to help you heat the mixture in the microwave on a high setting for about 50 seconds. The mixture should begin to bubble and become translucent. That means it is partly see-through, like baking parchment.

3 Use the oven mitts to remove the bowl from the microwave and let the mixture cool down.

4 Once the mixture has cooled down, knead it until it is smooth and soft. You will now be able to mould it or cut it into different shapes with cookie cutters. Let the moulded biodegradable plastic harden for about 24 hours.


Let’s Investigate

When something biodegrades, it means that microorganisms (living things such as bacteria that are too small to be seen without a microscope) eat away at it until it becomes part of the soil and air again. Is your plastic biodegradable?

To find out, try burying some in a plant pot in your backyard and see what happens to it. Remember to keep the soil moist because microorganisms are living things and need water to survive. Dig the plastic up after a couple of weeks and see what has happened to it. If it hasn’t changed much, leave it for longer and look again.

Inside the Science

When you first stir the cornstarch and water together to make the plastic, they mix but the molecules remain quite separate. The starch molecules are already polymers – long chains of repeated patterns – but they are all wrapped up like a ball of string. When you heat anything, you give it energy, which makes the molecules inside move faster. So, when you heat the cornstarch mix, the starch molecules move more and more until they unravel into long strings, which then get tangled up with all the other strings nearby. They also get tangled up with the water molecules, which can’t escape from them. That’s your plastic.

Craft idea from Super Slime! by Susan Akass, published by CICO Books (£9.99)

Photography by Terry Benson © CICO Books. In Super Slime! Susan Akass offers a brilliant variety of safe homemade recipes to give kids kudos in the classroom for making their own slime. As well as helping kids develop creative skills, Susan explains the science behind their squishy, stretchy creations.


Heather Black

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