- An oven
- An ice cream wrapper with printing on it (well-known brands include Paddle Pop and Icy Pole)
- Paper towel
- A baking tray
- Aluminium foil
- An oven mitt
- A spoon
What to do
- Preheat the oven to 250 °C.
- Being careful not to rip the ice cream wrapper, open the wrapper and remove the ice cream. (Eat the ice cream now or put it on a plate in the freezer for later!)
- Carefully open the seams of the wrapper until it is a flat rectangle.
- Wash the wrapper with water and detergent.
- Thoroughly dry the wrapper with some paper towel.
- Cover the bottom of the baking tray with aluminium foil.
- Place the wrapper on the centre of the baking tray. Make sure the side with writing faces upwards.
- Place the baking tray in the oven and leave for 2 to 3 minutes. Watch what happens to the wrapper during this time.
- Use the oven mitt to remove the baking tray from the oven.
- Flatten the edges of the wrapper with the back of a spoon.
- Allow the wrapper to cool (about 5 minutes).
- Use the scissors to cut off any rough edges from the wrapper.
Questions to ask
What happened to the wrapper while it was in the oven?
What do you think would happen if you left the wrapper in the oven for longer?
What happens when you try this using different types of wrappers, like the wrapper from a chip packet?
Everything is made of atoms. Atoms can join to form groups called molecules. Plastics are made from very long molecules called polymers. Polymers look a bit like a chain and are naturally found in a curled-up and tangled state. To make a sheet of plastic, like an ice cream wrapper, the polymer chains are stretched out. When the wrapper is heated, the polymer chains start to vibrate violently. This causes them to go back to their original, curled-up state. They are shorter when they curl up, so the wrapper appears to shrink.
Ice cream wrappers are made from a kind of plastic called polyethylene terephthalate, or PET. PET is cheap, easy to work with and light. PET bags can be sealed by pressing the edges together while heating them. This makes PET a good material for packaging things like ice creams.
The heat-sealing quality of PET polymers is what allows the ice cream wrapper to shrink in the oven. When the wrapper shrinks, the overall shape of the package stays the same because the polymer chains point in all directions in the sheet. It might get thicker, though, when the polymer chains curl up. The labelling is just a very thin layer of ink, so it also shrinks with the rest of the packaging.
Did you know
PET is the easiest plastic to recycle. Recycled plastic can be used to make rubbish bins, park benches, playground equipment, decks and kayaks. But when plastic is thrown away as waste, it can take 50 to 80 years to decompose!