UV Resistant Polymer

[BillDog103]

I realize that this question is asked all the time, but I need to take it to a new level. I need a polymer that can survive in an extreme UV environment. I'm not talking about outside, exposed to the sun, I mean inside a laser. Currently I am using Ultem 3000 but it is still breaking down after a period of time. I have heard the Imides are the toughest but I can't find any standards testing to use as a real comparison. If any one has any suggestions for a material or a link to a good source of information, I would be very grateful. Thanks in advance.
-Bill

 

[Demon3]

Does the polymer have to take high heat? Your present choice would suggest yes. Does the solution have to be one polymer? For example a coating to block UV and then another polymer for mechanical properties would be one option.

Furthermore the UV stabilisation package in the polymer is as important as what polymer you choose. A combination of a UV adsorber (e.g. Chimasorb) plus some HAS (hindered amine stabiliser such as a Tinuvin or similar) would be the usual choice.

Some UV resistant polymers include PMMA and polycarbonate. Does the polymer have to have mechanical properties like a certain modulus, HDT/Vicat, impact reistance? Does it have to be transparent?

 

[BillDog103]

Thanks for replying Demon3,
The temperature inside the cavity is held around 40 C by a deionized water flow. This brings up the second important requirement, the material should have a porosity of 0 or very close to it. I am not sure about coating a substrate. The coating can not out gas, because it is a sealed chamber with many optics and high energy. If I did apply a coating to the Ultem, what would happen to the coating over time? Does it degrade and how is it applied? THe part has some deep cavities that may be hard to coat or to cure the coating in.
I think my optimal solution would be a stable polymer.

The material should be harder than PTFE but not neccesarily as hard as PEEK.

Is there a source for rating UV resistance? I have found some information at NIST.gov but nothing like what would be found in a list of mechanical and electrical properties datasheet. All I ever find is A for acceptable or E for Excellent. I need an actual measurement.

 

[Demon3]

Hello, the normal UV testing is a Xenotest where you expose to quite intense UV in order to accelerate the testing compared to leaving outdoors. These tests are standardised and the equipement is not so expensive. A Google search for "Xenotest" will give lots of hits. Quite often you measure the colour change of the polymer after a number of hours, e.g. up to 4000 hours or so for a very weather stable polymer. Alternatively you can age test bars (so-called "dog bones") and then measure mechanical properties (usually impact resistance or elongation to break) after ageing to check for degradation.

 

[patprimmer]

A good pure grade of PMMA is virtually impervious to attack from UV.

PMMA of PTFE are by far your best choices if the mechanical properties are suitable. PTFE can be made harder by addition of fillers.

PET also has very good UV resistance, but not in the same league as PMMA or PTFE.

Regards

eng-tips, by professional engineers for professional engineers
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[Pud]

I thought PMMA was good for UV as it is transparent to it? (or at least some of it!)

Cheers


Harry

 

[Demon3]

An easy way to dramatically improve UV resistance is addition of 3-4% carbon black.

 

[patprimmer]

Pud

You are correct.

For the UV light to do damage it must be absorbed. PMMA is totally transparent to UV light, so it is not damaged by it.

Carbon black is not necessary to protect PMMA from UV light. Also, 3% is quite a lot.

For materials subject to UV degradation, carbon black will protect the matrix, but will offer no protection to the surface.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Demon3]

Here you can find some platable polymer compounds. Plate the part with a layer of metal will be very good for the UV resistance.

http://www.rtpcompany.com/info/flyers/platable.htm