Most kids know about Shrinky Dinks®. These cool items have been around since 1973 and were a big hit in the ’80s. They are a great craft project for turning artwork into useful items such as jewelry, key chains, or miniature ornaments. Did you know that you can make your own shrinking plastic crafts using common, everyday items in your house?
Materials
• Clear recyclable #6 plastic, such as cookie trays, tops of take-out packages, or plastic cups*
• Baking sheet
• Oven at 325 °F (Toaster oven works great)
• Oven mitt
• Parchment paper or aluminum foil
• Permanent markers
• Scissors
• Optional: Metal spatula, hole punch
*The plastic does not need to be flat.
Be safe!
Double-check that the clear plastic is clearly marked #6. Heat the plastic in a well-ventilated area only. Adult supervision is required when using the oven.
Preparation
Make sure the plastic is clean and dry. Preheat the oven to 325 °F and line a baking sheet with parchment paper. Alternatively, you can use a large piece of aluminum foil without a baking sheet (see below).
Experiment
Cut the plastic into a fun shape and draw a colorful design on it using permanent markers. The plastic will shrink to about one-third of its original size upon heating, so don’t make the design too small. If you want a hole in the item for use as a keychain or ornament, punch a hole in the plastic before heating it. Place the plastic artwork on the parchment-lined baking sheet, or directly onto aluminum foil. Place the baking sheet on the middle rack of the oven and watch what happens over the next 2 - 3 minutes. The plastic might curl up during heating - this is normal and it should flatten out after continued heating. After three minutes, use an oven mitt to remove the baking sheet from the oven. You can use a metal spatula to flatten the plastic once it comes out of the oven. Let the piece cool to room temperature before touching it with your hands.
What’s happening?
Recyclable #6 plastic is a compound called polystyrene. When the plastic is manufactured, it is heated, rolled out, and rapidly cooled. This causes the very long-chain polystyrene molecules to line up in an orderly arrangement. When you reheat the plastic, the molecules return to a more natural and less orderly state where they are all bunched together. The law of conservation of mass** tells us that the mass of the plastic doesn’t change, even though its area decreases significantly. Something must be changing! Compare the thickness of the plastic before and after heating. The miniature plastic is much thicker than the original. You can compare this to taking a sheet of aluminum foil and crumpling it up into a tight ball and then flattening the ball. The surface area decreases but its mass stays the same.
**Applying this principle assumes the plastic doesn’t evaporate or undergo a chemical change where a gas is released during heating. This assumption is valid.
References
http://www.chymist.com/Shrinky%20dinks.pdf
http://myhappycrazylife.com/diy-plant-markers-shrinky-dinks/
https://www.thechaosandtheclutter.com/archives/plastic-cup-shrinky-dink-ornaments
To view all past “ChemShorts for Kids” activities, go to:
https://chicagoacs.org/ChemShorts
