Here’s a subject you wouldn’t think would crop up in this country, the affects of Ultra Violet on your plastics. Well if your component is going to live outside, it’s something even we in the UK must seriously think about and particularly if your components are lucky enough to get exported on their holidays abroad.
The basics of UV
From a simplistic point of view, you can think of UV as basically a form of radiation which we’re getting from sunlight, its invisible to the human eye but will cause degradation in polymers. In other words, if your plastic bits are living outside, they’re going to get affected by this UV radiation.
What happens to plastics?
The actual plastic begins to “age”, the structure of the material begins to break down, in technical terms, the complex chain of polymers literally begins to unravel, turning it back into monomers again.
The result to us is that this tough plastic component we once made begins to gradually fail. Rather than being the strong, tough and hard wearing part it once was, it’s now gradually becoming a brittle component that can crack and crumble fairly easily, as you can imagine, this could be pretty bad news in certain situations.
Are all plastics the same?
We can be fairly sure that the engineering plastics we’ll ever be using are all going to be affected, as always its also fair to say that some are worse than others,
The good guys: PTFE, PVDF and PEEK
The bad guys: HDPE, Polypropylene, Nylon 6 and UHMWPE
The ugly guys: Acetal, PVC, Nylon 66, ABS and Polycarbonate
Tips that may help
To improve the life of a component, it would be an advantage if the plastic used was black, this is because the carbon in the black pigment will absorb some of the radiation to extend its life by some amount but its certainly not going to extend it substantially. Before you ask, slapping some factor 50 on wont help either.
Guaging the life expectancy
Here’s the “million dollar question”, how long will a particular plastic last? Well coupled with another saying, “how long is a piece of string?” its impossible to say, but common sense suggests things that will affect it are simply: how long will it actually be in direct sunlight? Can it be shaded? Is it south facing? What country? Even, what part of the country?
What about UV resistant grades?
Manufacturers have created UV resistant grade plastics for the mass industry particularly manufacturers of Polycarbonate who have had to develop a UV resistant grade because of its use in glazing applications. But in general terms, the volumes just arn’t there so the availability of specific UV grades to the engineering plastics fraternity is pretty sparse.
In summary
If its going to live outside, probably best not make it out of natural Acetal and always try and use a black colour plastic where possible. If you’re using polycarbonate such as Lexan for glazing always ensure its the UV grade. The bottom line though is that if your component is going to live in direct sunlight for all its life then UV is definitely going to have an effect which certainly needs to be taken into consideration.
