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Name: Hamish 
Status: student
Grade: 6-8
Location: CA
Country: USA
Date: Summer 2013


Question:
I am working on a science project about photo-degradation of plastic film. My question is how much degraded a plastic film should be to say that it was 100% photo-degraded? The plastic film I am photo-degrading is turning into dust when I touch it, what level of degradation is that?



Replies:
Hi Hamish,

Thanks for the question. You will need to define what you mean by photo-degraded. 100% photo-degraded could be that the film becomes translucent and lets through only blurry images. Or it could mean that the film turns to dust when you touch it. As long as you clearly state in your science project what you mean by 100% photo-degraded, you will be doing a good job.

Thanks Jeff Grell


Hi Hamish,

In fact, the term "100% degraded" is impossible to define, and therefore rather meaningless. When some types of plastics are exposed to Ultraviolet light, it begins to break the plastic's long polymer chains into shorter fragments. This weakens the plastic more and more with longer exposure. Gradually, the plastic film (in your case) gets easier and easier to crumble. But there is no definite point where you can say it has "fully degraded" and that no more degradation can occur.

For example, take polyethylene film. This is made from small molecules of ethylene gas, joined into long chains to form a polymer. UV exposure will break the long chain molecules of polyethylene, into shorter fragments, and the film will gradually lose its strength until it crumbles more and more in your hands. But this is not the end of it. I suspect that with even longer (much longer!) UV exposure, much of the polyethylene chains that make up the film, will break down into ethylene gas and disappear into the air. So, once again, UV degradation is a gradual, continuous process that has no definite "end point". This rather like asking when a piece of wood that is rotting, can be said to be "fully rotten"!

Regards, Bob Wilson


You do not say what the plastic is. Without that information it is hard to give a specific recommendation. What is its viscosity in a solvent? Is it water soluble, or not? Is the ?dust? soluble in water or other solvent? ?Turning to dust? is not a very quantifiable measurement.

Vince Calder


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