[katieHaylor (OP)]

Greg asks:

Why do white or light coloured plastics degrade in sunlight faster than dark or black shades of the same plastic?

Since a white or pale colour means that most of the light hitting the surface is reflected, and a black or dark colour infers that the majority of the light is absorbed, surely the light coloured plastic should degrade more slowly than the dark ones that adsorb all the light energy, have to dissipate it into their structure and therefore would be expected to degrade faster than their lighter counterparts?


What do you think?

[Colin2B]

It isn’t the visible light that degrades plastic but the uv which is not always reflected and penetrates the surface breaking the internal bonds. Heavy loading with black or grey pigment prevents this penetration.

[glot]

If I have a red and a black plastic in the sun, the red fails a lot earlier. Red seems to have this issue in other outdoor things.

[glot]

I use a PVC that is heavy on carbon black and Titanium dioxide? It has a very long lifespan.

[Bored chemist]

Titanium dioxide actually increases the rate of degradation by sunlight in some cases.
This sort of thing happens.
https://pubs.acs.org/doi/abs/10.1021/jp0540914

The stuff used as a pigment is sometimes coated with silica to prevent this.