Which Plastic is Which Shrinking Cup Experiment

which plastic is which shrinking cup experiment activity craft left brain craft brainaffiliate disclosureI just received a copy of the amazing book 101 Kids Activities {affiliate} written by Holly and Rachel, the smart women behind Kids Activities Blog.  The Babe had a blast picking out which activity she wanted to do and landed on the Shrinking Cup Flower Decorations. Then she picked the DIY Bouncy Ball. Then Tinfoil Relief.

101-kids-activities-that-are-the-bestest-funnest-ever-book-cover-650We basically spent all day doing projects from the book.

I love this book because there are so many unique projects to do. Plus the instructions are really easy to follow and include ways to modify the activity for younger and older kids. Perfect for real life projects with the littles.

Here’s how the Shrinking Cups went…

Which Plastic is Which?

We had two different types of clear plastic cups in the cabinet, so I decided to do a little experiment to find out which one would make the best decoration. You know those recycling codes on the bottom of your plastic containers? They tell you what type of plastic they are. We had #1 and #6. Here’s a quick explanation of the typical plastics used in consumer products these days.plastic recycling table final left brain craft brain

Shrinking the Plastic Cups

To make the decorations, 1) Color the cups with permanent markers. 2) Cut 1-2″ slits in the top rim to help the cup separate. 3) Place on a baking sheet and bake for one minute at 350° F. Watch carefully so they don’t burn and wait 10 minutes before touching the plastic after they come out of the oven.

shrinking plastic cup experiment steps left brain craft brain

What happens when you heat the cups? The heat is changing the alignment of the polymer chains within the plastic. In the cup manufacturing process, a polymer resin is heated, extruded, rolled into flat sheets and then molded. This process aligns the polymers into an orderly pattern, but the heat of the oven returns them to their naturally disordered, clumped state.

How come this activity only worked on the #6 polystyrene cup?  Only one of the cup types melted. The #6 PS melted but the #1 PETE just turned a bit white at the edges.  The type of polystyrene used in the cup has a lower melting point than the polyethylene terephthalate in the #1 cup. We would need an oven set to almost 500° F to melt the PETE. When I put the #1 cups under the broiler they finally started to crumple and melt. But they weren’t nearly as pretty as the #6 cups!

butterfly shrinking plastic cup craft left brain craft brainOne of the #6 cups melted into a perfect butterfly shape. We must be obsessed with butterflies these days because we’ve been making a lot of them! (Butterfly Catch Game and Butterfly Flower Pots) And apparently obsessed with polymers too! For another great way to learn how polymerization works, check out my other post Polymer Science 101: Homemade Fruit Gummies.

Need more fun ideas for stuff to do with the kiddos? Pick up your own copy of 101 Kids Activities!  {affiliate}


10 thoughts on “Which Plastic is Which Shrinking Cup Experiment”

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