Just ordered my UV bulb!!
Just ordered my UV bulb!!
Thanks for the science lesson :P Aw, so you're saying even plastics that yellowed due to UV exposure and were restore with Retr0bright, will still un-de-yellow when exposed to oxygen?Originally Posted by Merlin
No, the UV light is the key to it all. Bromine has one important unique property that creates this phenomenon; Bromine molecules vibrate under UV light, specifically around 320nm.
[Science bit]
When UV light hits Bromine molecules, they begin to vibrate, exciting the outer shell of electrons. Those that did Chemistry at school or college might remember that Bromine has seven electrons in it's outer shell, as it's one of the Group VII halogens.
The Bromine really wants eight electrons in the outer shell, so it starts to hunt for any molecule that has one to share. Oxygen is one of these molecules and the O2 splits into two O- radicals then shares it's electron with the Bromine via a co-ordinate bond.
Co-ordinate bonds are the weakest of the chemical bonds and hence they are the easiest to break. By putting the plastic in contact with a destabilised peroxide mixture under the same UV that makes the Bromine vibrate, we provide enough energy to break the bond with the oxygen radical and a hydrogen radical H+ attaches itself, taking the bromine back to a stable six electrons in the outer shell (electron shells like even numbers).
The other factor is that brominated flame retardants are usually liquids. I know that you maybe think of plastic as a solid, but it isn't; it's a very small lattice structure that things can pass through. What happens is that the hunger of the Bromine for electrons is so strong that it gradually migrates through the plastic lattice to the surface. This only happens when UV light is shining on the plastic.
So, the optimum conditions that you need for this reaction to proceed either way are UV light, Bromine and Oxygen. Take any of these away and nothing happens. A lot of people described the Retr0bright process as simply 'bleaching' the plastic. If that were true, the Retr0bright process would work in the dark, which it doesn't. Try it for yourself, the parts just get wet, we've proved that.
The easiest one to take away from the reaction is the oxygen via a lacquer coat, as this acts as a barrier to the oxygen. The parts inside don't go yellow as they aren't exposed to UV light. If you use a lacquer with a UV filter chemical in it (usually an adsorber or an up-converter, both types of UV blockers) , then the problem should be cured.
[/Science bit]
Plastic that has yellowed inside and outside has just oxidised (the polymer has degraded) and that is usually permanent.
Last edited by Merlin; 23rd May 2012 at 21:10.
Yes, exactly that.
Retr0bright is not destructive, so it's reversible to previous badly yellowed state.
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Oh, I thought it restored it to the state it was in when it was new, and it won't yellow again unless exposed to UV light, as is what happened to cause it to yellow in the first place.
Are the any particular products you would recommend for sealing the plastic? Obviously I'm looking to keep the same texture and not have it any glossier than it would normally be.
Get a satin-matt acrylic lacquer with a UV filter in it and 'float' the coat on to the parts from about 8 to 10 inches away. That way, you will retain the textured, grainy finish of the parts.
The future's so Retr0bright, I gotta wear shades.....
As rkauer said:-
"Retro computers seems like an orgasm: it is always better to have a real one than fake it".
Awesome, thanks for that Merlin! Now I just need to figure out what stores sell that kinda thing, craft store maybe?
I love the depth of knowledge and information that is available here. Its great we have such knowledgable members. Thanks MerlinNo, the UV light is the key to it all. Bromine has one important unique property that creates this phenomenon; Bromine molecules vibrate under UV light, specifically around 320nm.
[Science bit]
When UV light hits Bromine molecules, they begin to vibrate, exciting the outer shell of electrons. Those that did Chemistry at school or college might remember that Bromine has seven electrons in it's outer shell, as it's one of the Group VII halogens.
The Bromine really wants eight electrons in the outer shell, so it starts to hunt for any molecule that has one to share. Oxygen is one of these molecules and the O2 splits into two O- radicals then shares it's electron with the Broming via a co-ordinate bond.
Co-ordinate bonds are the weakest of the chemical bonds and hence they are the easiest to break. By putting the plastic in contact with a destabilised peroxide mixture under the same UV that makes the Broming vibrate, we provide enough energy to break the bond with the oxygen radical and a hydrogen radical H+ attaches itself, taking the bromine back to a stable six electrons in the outer shell (electron shells like even numbers).
The other factor is that brominated flame retardants are usually liquids. I know that you maybe think of plastic as a solid, but it isn't; it's a very small lattice structure that things can pass through. What happens is that the hunger of the Bromine for electrons is so strong that it gradually migrates through the plastic lattice to the surface. This only happens when UV light is shining on the plastic.
So, the optimum conditions that you need for this reaction to proceed either way are UV light, Bromine and Oxygen. Take any of these away and nothing happens. A lot of people described the Retr0bright process as simply 'bleaching' the plastic. If that were true, the Retr0bright process would work in the dark, which it doesn't. Try it for yourself, the parts just get wet, we've proved that.
The easiest one to take away from the reaction is the oxygen via a lacquer coat, as this acts as a barrier to the oxygen. The parts inside don't go yellow as they aren't exposed to UV light. If you use a lacquer with a UV filter chemical in it (usually an adsorber or an up-converter, both types of UV blockers) , then the problem should be cured.
[/Science bit]
Plastic that has yellowed inside and outside has just oxidised (the polymer has degraded) and that is usually permanent.
What do you mean by "float"?
I just used retr0bright on my A500 and accesories and don't want to loose the brilliance.
Another question, I just made the liquid version and soaked (weighted down with fishing line and lead weights) the items in a clear plastic tub and a UV light on them. How long is the solution good for? It is still creating bubbles today and I made it on Saturday.
Thanks!
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What I mean by 'floating' the lacquer on, is that you want the paint to have lost a lot of solvent by the time it hits the surface, deliberately creating the wrong paint effect. Let me explain about paints and lacquers for a moment.
[Science bit]
Paints and lacquers don't normally have one solvent in them, they have several, designed to evaporate (flash) off at different rates. The lower bioling solvents just carry the paint to the surface as a fine mist, whereas the higher boiling solvents tend to hang around, to make the surface of the paint or lacquer smooth; this is called coalescence. Coalescence is what makes the paint film join up together into one smooth, glossy film - not quite what we want.
By spraying the paint from too far away, you deliberately defeat the low boiling solvent's action, so the droplets are much higher than normal in solids when they hit the surface. You still want some of the higher boiling solvents there as these make it stick to the plastic.
What you are deliberately creating is an effect that paint sprayers call 'orange peel', since that's what it looks like close up. These pictures show what I mean.
See what I mean? By putting the coating on 'wrong', we re-create the textured finish of the plastic.
[Science bit]
Does that make more sense now, as to how you apply the lacquer?
A good arts and craft shop or an automotive paint shop should be able to help you with a UV protectant lacquer. they also get used a lot on aircraft, to stop paint fade, as the UV up high is a lot stronger. Krylon UV-Resistant Clear is a brand I would recommend, as it has very good adhesion to plastics.
The future's so Retr0bright, I gotta wear shades.....
As rkauer said:-
"Retro computers seems like an orgasm: it is always better to have a real one than fake it".
Hmmm, having a bit of a tough time finding a suitable lacquer. The closest I've been able to find is at an art supply store, it's not an acrylic lacquer, but it's a spray designed to seal plastics. No UV protection though. Any clues if this stuff would be useful?
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