Cornstarch and polystyrene packaging

We've had a couple of things delivered recently which have come with packaging chips to protect them inside a cardboard box. We received two types, polystyrene (styrofoam) and a cornstarch biopolymer.  Aside from playing with the cardboard boxes, which provide plentiful amusement here, I thought I could show my almost 4 year old how the cornstarch and polystyrene were different.

Cornstarch (left) and polystyrene (right)

I started out by asking my son why he thought you might put them around something breakable when you sent it in the post, and - possibly informed by the endless calamities that befall Postman Pat in the TV shows - he thought they would protect it. We talked about why - the air inside them can squash a bit to cushion an impact, and he tried to squash the two types with his hands. The corn packaging chips squashed more readily and didn't bounce back to shape, so he didn't think they were as good. 

Adding water

Next I got him to pour some water on each. The first thing he noticed was that they floated - this is due to the air inside them making them less dense than water. The next thing was the cornstarch chips started bubbling, and we talked about how this was air coming out of them. He pushed them into the yoghurt pot and was impressed at the quantity of bubbles but disgusted by the sticky goo on his hand! Once the goo was washed off(!) we watched as the cornstarch mostly dissolved, leaving a small amount of residue.  He tried to repeatedly push the polystyrene chips under the water and got a few small air bubbles from squashing them hard, but several hours later they were still intact and he agreed that they didn't dissolve in water!

We discussed when it might be a good idea to use the cornstarch packaging (for most uses!) and how it would break down in landfill, so it's not environmentally damaging (aside from manufacturing it, although we didn't talk about the potential environmental impacts of this).  I asked him if he thought it'd be good to make a cup for hot drinks from, and he thought not, the drink would come through the cup pretty quickly!  He's right, and polystyrene would work better here (but reuseable cups would be preferable).

Cornstarch mush and intact polystyrene

I wasn't sure if this was going to prove to be a boring activity, but he was pretty excited to explain it to my husband later.  Hopefully it follows on from our packaging in the sea experiment earlier in the year to help him start to think through how we need to choose materials which are fit for purpose and better for the environment.