Retrobright ozone method

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PhilC
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Re: Retrobright ozone method

Post by PhilC »

So if you wanted the best results as quick as possible, what method would you use?
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Re: Retrobright ozone method

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PhilC wrote: Tue May 12, 2020 6:22 pm So if you wanted the best results as quick as possible, what method would you use?
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Re: Retrobright ozone method

Post by terriblefire »

Ozone gas is what trump wants you to breath lol
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Re: Retrobright ozone method

Post by graealex »

It's funny how there is not a single canonical explanation for what happens exactly due to breaking down of BFRs from UV light in plastics. Some claim that free bromine radicals bond to oxygen (?), as if bromine actually wants to be bound to oxygen. Some claim that retrobrighting forms the relatively stable HBr from those oxides, which is colorless, but that doesn't really explain why Ozone or just leaving it out in the sun would have any effect at all. My theory is that the degradation of ABS polymers, which usually just gets oxidized, in combination with free bromine, which takes the place of oxygen when saturating the polymers again, causes the yellowing. Introducing a radical, usually HO, partially reverses this. Just my theory, most of that is above my paygrade.

Anyway, the key is reaction speed, and some reactions won't even happen bellow a certain temperature. UV catalyzes decomposition of unstable compounds like H2O2 and O3. Ozone is problematic because at room temperature it decomposes by itself with a half-life of 20 minutes anyway. To make that effective and somewhat fast, you'd probably want heat, UV and a constant supply of ozone to replenish it. You'll see success with people using hydrogen peroxide and UV-A lights, which really isn't that energetic, as hydrogen peroxide is generally photosensitive, not just to UV, and you'll also see success with people just using hydrogen peroxide or sodium percarbonate in a cooking pot, as heat is all that is required to decompose either of them and create free radicals. You'll see TAED in recipes, because it lowers the decomposition temperature. That's basically what is happening when you use a product like "Vanish" in your washing machine: sodium percarbonate, TAED, and some heat from the washing machine itself that releases free radicals at an appreciable speed to bleach your laundry.

So for any tests, the main question isn't "does it work?", but rather "how fast is it?". Just ozone in a bag probably works somewhat, but at a rate that is impractical. Especially since without replenishing it constantly, the concentration of O3 will go down significantly within hours.
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Re: Retrobright ozone method

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If you look at the first post I had a ozone generator. But overall I don't think it really made any difference in the experiments.
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Re: Retrobright ozone method

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Another odd thing which then supports "sunlight" as causing the troubles... even though leaving the cases out in sun light lightens cases...


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Re: Retrobright ozone method

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It very much depends upon the formulation of the plastic, and which batch of plastic and from which supplier at the time.

I know that the TT plastic gets sun tanned rather than bleaching. Mac Plus cases bleach. Mac SE/30 cases tan.

As you saw there, some keys tanned and some bleached.

Also, the effect is like taking a photograph. Often the darkening happens a long time after the exposure to light. The "film" develops, often in the dark, usually helped by heat.
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Re: Retrobright ozone method

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Still doesn't make sense though.. as if I put tanned plastic out in the sun, it lightens up.. so how can the sun be the cause AND the solution..
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Re: Retrobright ozone method

Post by stephen_usher »

Well, as I said, some plastic never bleaches.

Anyway, what the light is doing is breaking bonds in a chemical, creating the potential for the molecule to break, changing its colour sometime later either after a random time or when something changes, such as heating. In some cases it will change the chemical to a different oxydation state, bleaching it, but this may not be stable, so it will revert its colour later. All this depends upon the precise formula of the chemical being affected, and this is usually the flame resistant additive.
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