SeeK > Themes > Materials > Plastic Magic logo

Plastic Magic

AIM:

To introduce plastics and polymers and their behaviour when heated

CURRICULUM LINKS:

 

KS2: Sc3 Materials and their Properties, Changing Materials. 2 (b)

TIME:

20 minutes. 5 minutes explanation, 15 minute badge making.

MATERIALS REQUIRED:

Per class:
* teacher/adult only

  • 1 hot air gun (as used for stripping paint)*
  • Several heat proof mats*
  • 1 pair of long armed tongs*
  • A well ventilated area or fume-cupboard*
  • WHSmith's T-shirt pens (WHSmith's are the best pens for this and from experience best to cover the label on the pen with thick tape if used in class)

Per child:

  • 1 plastic vending cup
  • 1 small sticky label
  • 1 safety pin

METHODS:

* teacher/adult only

  • In a well ventilated area prepare a flat disk in advance by heating a cup*
  • Ensure the cup is held down well using the tongs, and heat the top and sides of the cup evenly with the hot air gun in a circular action (best to practice this!)*
  • Gather the children together in front of your setup for heating the cups
  • Ask them if they know what the disk used to be
  • Explain to them that it used to be a plastic cup
  • Describe how the plastic is made up from atoms which are joined together in long chains
  • Explain that the chains of 'polymer' are under a lot of stress when they form the cup shape
  • Demonstrate what happens to a cup when it is heated*
  • Explain that as the polymer chains are heated , or given energy, they choose to relax back into their more preferred and less stressed arrangement - the flat disk
  • The reverse process to that demonstrated, for forming cups etc., can be explained at this point.
  • Each child can make a badge from a cup to take home

To Make the Badges:
* teacher/adult only

  1. Think carefully about how the cup shrinks, use the felt pens to decorate the cup on the outside, including your name
  2. Heat the cup as described above and allow to cool*
  3. Stick a safety pin to the back of the cup using a sticky label
  4. Wear the badge with pride!

NOTE: Alternatively, heat the cup on a baking tray in a preheated oven (Gas Mark 3 / 325°F / 160-170°C), for approximately one minute. This method is not as visual, but safer.

THEORY:

  • Plastics are made from atoms joined together in long chains, known as polymer chains, which are a bit like cooked spaghetti.
  • When the plastic is in the form of a cup the polymer chains are stretched out along the length of the cup. This requires a lot of energy.
  • When the plastic cup is heated, some energy is put into the polymer chains so that they can relax into their usual random spaghetti-like arrangement.
  • Plastic cups, margarine and yoghurt pots are all made using this concept. The plastic starts in flat sheets before being heated and vacuum formed into the cups/pots. The shape is retained upon cooling.
  • When these objects are reheated they will return to their original shape - in this case a flat sheet.
  • This is sometimes called plastic memory.

WEB LINKS:

The American Plastics Council - Hands On Plastics Jr.
Background information on plastics and educational games & activitie

Plastic Fantastic
Plastics the materials of the future - an article published in the TES magazine.

The Yoghurt Pot with a Memory Alternative way to conduct this experiment with adult supervision;

back to Materials