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Self Folding Plastics – Shrinky Dinks, the Next Generation

As you might know I’ve been working on a book of 365 (!!!) science experiments. In doing research for a project I cam upon some work on self-folding plastics being done at NC State University.

My first though was– I can do that in my kitchen!
And I did.
And it worked.
And you can do it too!

Self-folding plastics can be useful for packaging, electronics and remote deployment of satellites. Basically an object starts out flat. With the addition of heat and/or light it automatically assumes a pre-programmed shape.

The first work in self-folding plastics was done using a cheap, readily available commercial plastic. Polystyrene plastic (#6) is a thin clear plastic used, among other things, for take out containers. You might be more familiar with polystyrene as Shrinky Dinks.

That’s right, Shrinky Dinks. The vintage craft of the 70’s is now cutting edge technology.

Here’s how it works. Polystyrene is a polymer, made of long chains of molecules all jumbled up together. When the plastic is heated above 212F/100C those chains loosen up and the plastic flows. To make thin sheets and take out containers the polystyrene is stretched, molded and then cooled very quickly so it holds its shape. But when you heat the plastic up again the polymer chains contract back to their original shape.

To make your own Shrinky Dinks, just find a plastic take out container with #6 in the recycle symbol (I found mine at Brixx Pizza), cut out the shape you want, color it with markers, and put it in the oven at 325F for about 4 minutes. If you can, watch the plastic shrink. It will curl up and then magically flatten into a thicker, smaller version of the shape you started with.

There are so many questions you can investigate with shrink dinks! You can weigh the plastic before and after to see if it loses mass. You can cut out a 6 -inch square and see how small it shrinks.  You could calculate the volume before and after to see if that changes too.

But back to those cool self-folding plastics! Here is a video from Dr. Michael Dickey’s lab at NC State University.

As you can see all you need to do this at home is

  • polystyrene,
  • ruler,
  • scissors,
  • black ink (a china marker works best),
  • and a 250 Watt heat lamp.
    You might even have one of these already in your shower or if you keep snakes or lizards and use a heat lamp to keep your critters warm. If not, they’re about $8 at your nearest big box hardware store.

The basic idea is that the areas covered with black ink absorb the heat and shrink faster than the clear areas. The shrinking causes the plastic to fold. So all you need to do is cut out the shape you want and mark the folds with a black china marker. Place the shape on a white paper about 6-8 inches below the heat lamp and in just a minute your shape will fold up all by itself!

We did two trials and made videos of each.

Trial 1
The box has 1-inch sides. As you can see it was a little too big for the area heated by the lamp but it folded up fairly well.

Trial 2
This time we cut out a shape with ½-inch sides but the folding wasn’t uniform. I think I may have put the shape under the lamp upside down.

There is definitely lots of room for investigation here. As soon as I finish the book I want to try some more shapes and sizes.

If you want to learn more about self folding plastics check out this video about new inflatable self folding origami from MIT and this material created by scientists in China that can fold into many different shapes.