Aluminum oxide on plastic problem

[DanvilleJeff]

I have a several black plastic parts as part of a product that is placed in a large aluminum housing that is outdoors. The aluminum housing is painted on the outside, and the plastic is all exposed to the sun and weather. After several months, one particular plastic part becomes sort of "chalked over" with a loose film that is very reflective and looks white in the sun. The other plastic parts, made from a different material, are unaffected.

A chemist told me that the loose film is either aluminum or aluminum oxide from the environment that seems to stick to the surface of this particular plastic due to small fissures on the surface. Where could it be coming from? The aluminum sign should be covered in oxide that would be very stable I think. Does aluminum shed some amount of oxide in the outdoors?

Thank you,

Jeff

 

[unclesyd]

'White Rust' from Al will come off but normally requires some mechanical assistance.

Come back with the type Al you have.

If your plastic has cracks or fissues, surface degradation, you need to have the compunding formula changed to include more UV blockers.

 

[BillPSU]

The different plastice parts are probably made by different manufacturers and from different resins. I concur with unclesyd the part that is changing appearance probably has inadequate UV stabilizers. If possible find out what the part is made from. If you cannot get the information get some extra parts and perform a simple burn test and solubility test. It will narrow the type of the plastic. Today's plastics are made from an assortment of additives and fillers and complete analysis needs sophisticated equipment.

Whatever you find out changing the additve in the plastic will be required to stop the environmental changes.

 

[DanvilleJeff]

The aluminum alloy is 5052-H32, probably sort of generic stuff. I never heard the term white rust, although when I run a cloth over some bare aluminum it comes back gray...is that oxide?

The plastic that is "good" and does not turn white is a UL F1 material. Turns out the "bad" plastic is not an outdoor grade. I was able to order the parts with the outdoor UV resistant grade, so maybe I have solved the problem.

Now I would like to devise a test to see if I really fixed the problem. I was thinking of buying some 1-2 micron aluminum oxide powder and seeing if it is "trapped" by the old and new parts after some UV exposure. Although that is starting to sound like a lot of work.

Thanks for your replies,

Jeff

 

[BillPSU]

Talk with your part supplier and find out what resin it is made from and then you can talk to the resin supplier. I'm sure the resin supplier should be able to supply you test results on the resin. The product is probably a thermoplastic meaning the material basicly is melted and then resolidified. The test characteristics should be very reliable for parts made from this resin. If the material is a thermoset incomplete crosslinking can be a problem and processing variables could impact the outdoor duablility of the plastic.

I would avoid the UV testing and put that monkey on the part supplier if you really need the test.