Quote:
Originally Posted by ecomodded
I was told by a plastic welder who manufactures custom items for commercial and marine use that the black PVC and polyethylene last outdoors in the sun and that the white PVC & poly deteriorated quickly by the penetration of the sunlight threw the white color damaging the plastic,
causing it to be brittle and break easily.
I wonder if the white paints condition, not the color, is more subjected to sunlight damage by its light passing white pigment.
It dawned on me that NASA makes everything white so they can find it again !
or
could be "we never get to "SEE" the black stealth stuff"
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White pigment doesn't pass light. it reflects light. If it passed light, it would be called translucent.
There are several ways to impart UV resistance to PVC and polyethylene. The cheapest way is to add carbon black to the plastic. Carbon black absorbs UV and converts it to heat. A more expensive way to protect from UV is to add titanium dioxide to the plastic. Titanium dioxide (also used in sunscreen lotion), reflects the UV, but doesn't provide quite as much UV protection in plastics as carbon black, since the UV can do damage on its way in and on its reflected way back out of the plastic. A third way that can be used to protect polyethylene is to cross link its polyethylene chains, which is how they get the clear greenhouse films to last 4+ years in the sun.
Most of what NASA sends out of earth orbit isn't ever coming back, so they're not expecting to have to try to visually find it again. So that's not the reason they are white.