Kids, how would you like to make a bio-friendly corn-based plastic that was also biodegradeable? Grab your nearest adult partner along with these materials: 1 tablespoon cornstarch, a zip-seal bag, 1 tablespoon water, 2 drops corn oil, food coloring, and a microwave oven.
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
Here is what you do. Place the cornstarch in the zip-seal bag. Add the water. Seal the bag and mix the ingredients well by squishing the bag with your fingers. It should look like a smooth milky liquid. Then add 2 drops each of corn oil and food coloring, seal, and mix again. The oil helps keep the bioplastic from sticking to the bag. This order of addition is very important so follow the instructions closely.
Then your adult partner performs the next steps. They will open the zip seal just a tiny bit, put the bag in a microwave oven on a paper plate, and microwave on full power for about 20-25 seconds. The bag will be very hot (caution!) so your adult partner should wait before handling. While it is still warm, but cool enough that your adult partner says you can handle it, shape the plastic into a ball.
What’s happening? Before heating, the starch and water molecules combine physically in a liquid mixture, but do not permanently attach via chemical bonds. Heating causes the water molecules to move fast enough to penetrate and break up the cornstarch granules, which then tangle together to form polymers.
Compare the biodegradable plastic you made to the plastic zip-seal bag. To watch the plastic ball degrade, immerse it in water for a few days. Compare what happens to a piece of a zip-seal bag immersed in water for the same amount of time. Because the cornstarch polymers are weaker than commercial bioplastics, they readily break apart in water. Durable commercial bioplastics need heat, microbes, and much more time to biodegrade.
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Kathleen Carrado Gregar, PhD, Argonne National Labs
[email protected]
September 2010
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References:
C. Washam, ACS ChemMatters, April 2010, page 12; and
Field Guide to Utah Agriculture in the Classroom:
http://extension.usu.edu/AITC/teachers/elementary/fieldguides.html (Field Guide I, “Corn Starch Plastic”).
