This week we made our own biodegradable plastic and had hands-on (literally!) fun with sticky slime.
Slime
You have to feel this stuff to believe it. The children had way more fun playing with it than they’d expected. Best of all, it’s so easy – five minutes to make, a whole afternoon of fun!
What You Need
- Cornflour (cornstarch)
- Food colouring
- Water
- Cup, bowl, spoon
What You Do
- Put a cup of cornflour (cornstarch) into a bowl.
- Slowly add water, stirring all the time, until the mixture becomes a sticky paste (add up to about half a cup).
- Add food colouring and stir to blend.
- Have fun with your slime! Notice how it both flows like a liquid and sticks together like a solid.
The Science
Slime is a “non-Newtonian fluid” because it doesn’t conform to Sir Isaac Newton’s rules about how liquids behave. It’s made of polymers – long chains of simple molecules. When the chains are stretched out the liquid flows, but if you apply pressure the chains stick together.
What We Might Do Differently Next Time
This really is so easy. The only thing we’d do differently would be to be less concerned about the exact amounts of cornflour and water. You can always add more of either (or both). Cornflour is our new favourite science ingredient!
Home-Made Plastic
What You Need
- Starch (eg cornflour/cornstarch, potato flour)
- Glycerine
- Vinegar
- Food colouring (optional)
- Aluminium foil
- Wooden spoon/spatula
- Old saucepan
What You Do
- Mix together 1 tbsp starch and 4 tbsp water in a saucepan.
- Add 1 tsp glycerine and 1 tsp vinegar.
- Stir until blended.
- Put the saucepan on a low heat, stirring constantly.
- Observe the mixture change from a cloudy liquid to a clear gel.
- When the mixture is completely transparent and starts to bubble*, use the wooden spoon to spread it out on a sheet of foil.
- Wait a day for your plastic to set.
What Happened
Watching the mixture turn into a gel was very cool. *Ours never became completely transparent or visibly bubbled (we made three batches) but the plastic turned out fine. (For our purposes! We weren’t planning any industrial applications.)
I forgot to do step 6 for our first batch (I’m not great at reading instructions) so our red plastic came out in globules that would do nicely as fake jam!
Then we made green plastic in the same saucepan, without washing it, which resulted in a gross concoction that might be given away with the Beano (I’ll spare you the photo). I had to make some nice fresh-looking blue in a clean pan after that experience. (The kids were out playing in the snow by this point but – hey – I was having fun.)
What We Might Do Differently Next Time
- We might make some uncoloured plastic, to see if it turns transparent in the way the book describes.
- We might experiment with different quantities of glycerine, which changes the rigidity of the plastic.
- I wouldn’t use an ancient non-stick saucepan – bits of the non-stick coating came off in our plastic. The pan came completely clean after a soak so I’d use a regular, uncoated sort. Perhaps it’s time to invest in a dedicated science pan. 🙂
The Science
Like slime, plastics are made from polymers. Their chain-like structure makes them flexible enough to mould while soft, then strong when set.
What Does Each of the Ingredients Do?
Starch contains polymers. Vinegar makes the chains stronger, and glycerine makes them more flexible.
The Book
Both these experiments come from Science Experiments: Loads of Explosively Fun Experiments You Can Do. We’re very much enjoying our journey through the book. A few of the experiments call for materials that are tricky or expensive to source (dry ice, powdered alum) – we’ll skip those for now – but most are inexpensive household items. I love the way the materials and instructions are clearly laid out with plenty of pictures.
More Hands-On Science
Fizzy Fountains – Diet Coke Geysers and Home-Made Lava Lamps
We’re linking up with AdventuresInMommydom’s Science Sunday – thanks Ticia for hosting!
