yellowing acrylic lens

[dogbural]

Hi,

I have a light with an exterior lens made of cast acrylic.
After a year or so, I found the lens turned yellow.

The light was deployed near coastal area.
What is the possible root cause of this issue?
Just less UV content? Can the acrylic have the UV contents/resistance?

Regards,
MK

 

[TugboatEng]

Acrylic does not yellow in sunlight. Polycarbonate will yellow in sunlight. Coated polycarbonate included in the Lexan or Makrolon product lines have have ratings up to 7 years before yellowing starts to occur.

 

[IRstuff]

Have you not noticed that every acrylic headlamp covers is yellowed on older cars with non-glass covers?

https://www.ledil.com/wp-content/uploads/2018/01/PLEXIGLAS_Garantie.pdf

https://www.emcoplastics.com/acrylic-faqs/

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[TugboatEng]

I am confused by your comment.

From your link:

*There are three other clear plastics that do yellow in the sun and get confused with acrylic- Styrene, PETG, and Polycarbonate."

 

[btrueblood]

The link says that one specific brand of acrylic sheet will not yellow from sunlight exposure. Says nothing about a cast acrylic of unknown origin. Without UV stabilizers, Acrylic will degrade. If washed in strong bases (e.g. ammonia), acrylic will craze/haze. Sand and salt will haze/degrade acrylic as well (like you would get in a coastal environment).

Buy a headlamp lens polish kit at an auto parts store or your favorite online retailer, it comes with everything you need, and the instructions, to restore an acrylic or polycarbonate lens to reasonable clarity.

 

Acrylic or polycarbonate?
I understand that modern headlights use polycarbonate housings.

I use the polishing kits starting around 8-10 years and they work well, but I found I had to repeat every two years thereafter. What I wonder about is how much internal degradation is happening that can't be remediated by surface treatment.

I'm in a good mood today so I will walk away from ranting about everything that is wrong with modern automotive lighting systems (hint: everything). This fellow has an excellent site and is the most knowledgeable person I know.



"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[dogbural]

Thanks for the comments.

When I got the issued lens chemically tested and found out that there was no UV additives which made the lens yellowed.

Now if I would like to get a new supplier, how can I evaluate their quality?
Is there any usual test method (or testing ISO standard) that I should ask them for?

UV exposure, salt water testing or thermal degradation etc...

Regards,
MK

 

[TugboatEng]

ASTM G-154 and G-155 are accelerated weathering tests for clear plastics.

 

[dogbural]

Thanks