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
Plastics are made up of chains of molecules, when you stretch them, the molecules align, allowing bonding between the chains, this is crystallization, and results in opaqueness. In addition, when stretching the plastic on a microscopic level, voids form (this is crazing) these voids also result in opaqueness, so what you are seeing is a combination of the two effects. Even if the plastic doesn’t seem deformed on a macro level, it has been severely traumatized on a micro level.
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