Polymers and absorbency

How do nappies keep babies' bottoms dry? Nappies contain material that is designed to absorb water - called polymers. A polymer is a long chain of molecules made up of identical smaller parts, a bit like a long line of people holding hands. When water is added, the polymer soaks up the water and swells up.

Let's experiment

1. Cut the nappies open and shred the nappy filling INSIDE one of the rubbish bags. Close the bag and give it a strong shake, then re-shred the filling and shake again. Repeat the process until the filling no longer feels gritty.
2. Shake the bag gently to allow the super-absorbent polymers to fall to the bottom. Then remove the rest of the filling and put it in the other rubbish bag. Carefully transfer the polymer granules from the bottom of the first bag into the bowl. Remove any extra fragments if necessary.
3. Put a small amount of the granules in the glass or jar. Add a little bit of water to them. The polymer will swell up and absorb most of the water (you may have to wait a couple of minutes). Keep adding water slowly until no more will be absorbed - it can absorb over 500 times its own mass!
4. By adding water you will have formed a gel. Try adding some table salt (sodium chloride) to this gel and give it a stir - the gel should release the water again! The salt stops the water from binding so strongly to the polymer, causing it to release the water and shrink again.

Disposal: Put the nappy filling and the absorbent powder into the rubbish bin.