Why does transparent plastic become opaque when it breaks?

Question

My 7yo snapped the clip off of a transparent pink plastic pen. He noticed that at the place where it broke, the transparent pink plastic became opaque white. Why does that happen (instead of it remaining transparent throughout)?

This is best illustrated by the pic I took of the [broken pen](https://imgur.com/S8rasqb).

In: Physics

Answer 1

Basically, think of plastic like hair.

What do I mean? Well, plastic isn’t a solid material like glass or metal. Instead, it’s made of tons of small strands that look kind of like hair.

Now, think of a Queen’s hairdo – let’s take Elsa from Frozen as an example. Imagine her hair all nice pretty and shiny, and maybe a bit translucent. It’s all perfectly braided together, woven into a perfect bit of art. This is the clear state. It’s the state that plastic is when it’s fresh poured out of the mold.

Now give Elsa a case of bedhead. Her hair has been tussled, and bussled, and all sorts of messed up. It doesn’t look so pretty anymore. it’s lost it’s luster, and is all slept on with weird shapes and frizzle with a nightmare’s bluster, and that reflective sheen is nowhere to be seen. Plastic when you flex it, is like giving your material bedhead, and it does like that. Whatever original look it has, it gets all messy, and it changes. In both colored, and clear plastics, this “bed head plastic” tends towards white as the original color properties get all messed up as the strands of plastic rearrange out of their perfect pretty original form and start to reflect the light differently then they used to. Just like how bedhead hair isn’t shiny and light reflecting anymore.

To get the “pretty” hair back, you have to melt it down again and repour it at a foundry, which is the plastics version of going back to the hairdresser. Some plastics do this super easily, some not at all. Kinda of like how if you’re trying to get perfect straight hair to fold into a new Scandinavian royal hairdo, a woman like Elsa might be able to do it super easily, whilst a lady like Merida (From Brave) will have a nightmare getting her hair to lie straight enough to go into great braid, and it’ll be suuuper easy to get it back out of that shape.