I have a huge lot of yellowed Lego's, I want to try to de-yellow them. I have searched around the internet and this method seems the most promising:
I have a few questions about this : - What is happening at the surface of the ABS plastic ? - My knowledge on this subject is very limited, but would the process go faster when you perform the process in a ultrasonic bath ?
A bit of unrelated question : - Is it possible to combine the de-yellowing with filling any scratches gaps in the bricks ? It seems not to me because you have to have some filler in the solvent or break the bonds in the lattice, i guess ?
any help, information is welcome, I'm like to learn new stuff !! I can only understand it a little bit from a nanotech point of view.
Answer
According to the retrobright website the process involves the use of activated hydrogen peroxide and possible UV light. This won't work as well in an ultrasonic bath as the bath will keep out most of the light.
Yellowing is thought to be caused by some degradation reaction of some of the additives in the ABS plastic (probably brominated flame retardants, though it could be something else). What is probably happening is that the yellow products of that degradation are being destroyed by activated peroxide. The UV light probably helps this reaction along a little faster, possibly by activating the degradation products (a yellow colour is often a sign that there is a strong absorption of light from the molecules in the near UV).
If you follow one of the recipes on their site (with their safety precautions) it looks as though it should work for Lego.
Filling scratches, though, will probably not be easy as this is not a chemical problem but a physical one. The only effective way would probably involve remelting the ABS and recasting it which seems like overkill (especially since you would need original Lego moulds). Any chemical that will dissolve the ABS is more likely to destroy it than to selectively reshape the surface.
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