Why does leaving plastic out in the sun get rid of stains that refuse to wash out?


I saw someone asking how to remove a yellow turmeric stain from a blender cup & lots of folks recommended leaving it out in the sun to break down the pigment. Why does this work when water & scrubbing doesn’t?

In: 39

4 Answers

Anonymous 0 Comments

Water can only remove water-soluble substances. Soap can help remove some fat-soluble substances also. But the ultraviolet part of sunlight can break down substances that can’t be removed by either. Color, especially in plants and animals, is often a property of complex molecules. When they break, they lose their color. Bleach works the same way.

Fun fact: rust stains are unaffected by sunlight, and insoluble in water or fat. We use acids on those, because they convert the rust into other compounds that are water soluble.

Anonymous 0 Comments

Uv rays from the sun. Same thing as how it lightens coloured items in windows etc after a while. It also bleaches hair pigments and lightens coloured hair.

Anonymous 0 Comments

The sun is actually blasting the earth with hard radiation.

This constant bombardment gradually strips away the outer layer of materials, similar to how bleach works (and the effect is often called “sun bleaching”)

Always wear your sunblock, kids!

Anonymous 0 Comments

I learned this in organic chemistry once lol. Something about the radiation disrupting electron resonance. Eight years later I can’t explain it for *any* age group!