Corn Starch Plastic
- corn starch
- vegetable oil
- sandwich baggie
- microwave-safe plate or bowl
- microwave oven
- dropper (optional)
Plastic bottles, plastic spoons, plastic packaging, plastic bags… we use a lot of plastic. Plastics are made from polymers, which are super long chains of atoms. We love them because they’re cheap and super sturdy for how light they are. The problem is that they’re so sturdy that, after we throw them away, they can sit around in a landfill for a million years! Almost all plastics we use come from petroleum products, but recently more is being made from corn, and you can make some corn starch plastic at home!
Mix equal parts water and corn starch into a sandwich baggy. About a tablespoon works well, which is two large spoonfuls of each. If you’ve made oobleck before, this mixture should look familiar, except that this will be more watery. Next add 2-3 drops of vegetable oil and mix that in.
Now its time to microwave – but be careful! The microwave will heat up the gas in the bag, causing it to expand. We don’t want it to pop, so don’t seal the bag all the way. Instead, place it on a microwave-safe plate or bowl. Microwave (on high) for about 20 seconds. Do you observe anything as it heats up?
Take the plate out of the microwave, but don’t touch the plastic yet – it will be very hot! Let it cool for a minute, and when it is safe to touch take it out of the bag. Is it a solid or a liquid? What starts out rubbery and somewhat moldable will become hard and somewhat brittle as it cools more. Congratulations! You have made corn starch plastic!
Heating up the cornstarch makes lactic acid. Lactic acid molecules the combine into long chains of polylactic acid, or PLA. (Recall that "poly" means many, making it an apt name for lots of lacic acids strung togethter.) Polymers, with their long interwoven chains, give all plastics, including PLA, their special properties. The professionally made corn-based is sturdier than ours, and to the naked eye, it can't be distinguished from "normal" plastic. PLA is easier to compost, which means that under the right conditions it will break down into regular lactic acid in a matter of weeks instead of aeons. The catch is that it has a melting point of 114 degrees Fahrenheit, so using it for hot foods -- or leaving it in your car on a hot day -- is not a good idea.