No matter the color of the plastic, if you bend it, it turns white along the bent edge. There is an interesting scientific reason for this. It’s all explained in the following answers we gathered from the internet.
Plastics contain lots of very tiny holes. When the plastic is bent, the stress inside the plastic makes the holes get bigger. The empty holes in the plastic scatter the light, and so now the polymer reflects all colors of light instead of its original pigment, and so the plastic appears white.
When you bend plastic, you create imperfections in the plastic that changes the way light gets reflected back to your eyes.
Blue stuff is blue because it reflects blue light. Green stuff reflects green light, etc. But there’s another way to reflect light that doesn’t involve color: texture.
You know how mirrors are really smooth and they reflect light exactly? No matter what color hits it, it will reflect that color? Well, rough stuff (like rough on a really tiny scale) works the opposite. Any color that hits it gets jumbled and the reflection gets all weird form bouncing around all the nooks and crannies. That mixes all the colors of light together to make white.
Plastic is really smooth on the outside, but when you bend it, it makes a bunch of microscopic cracks that make the surface rough.
When you bend, stretch, or compress a material, you’re actually putting what’s called strain energy into it. You’re using some amount of force to make the material “give” a certain distance.
Now if you imagine instead of bending plastic you are squeezing a spring, then all of that energy that you put into squeezing the spring gets released when you let go and the spring returns to the exact shape it was before. The harder you push, the more the spring compresses and the harder it pushes back. In this case, all the energy you put into squeezing the spring is returned.
For some amount of bending, plastic can act the same way, springing back to its original shape after you let go. But if you bend it further still, you’ll find it starts to give a little easier and it doesn’t take as much effort to keep bending it. If you let go now, it will still spring back somewhat but it will stay bent. It wasn’t able to return all the energy you put into bending it, so what happened to that energy?
It became heat. The plastic gets warmer, and the same thing would happen to metal if you were to bend or stretch it past the point it could return.