In our last post, we stated that oxidants are needed to Retro-Brite plastic. These oxidants come in several forms, so lets focus on the most common one, peroxide. Recall, that peroxide breaks down into water and an oxygen radical (H2O2--->H2O2+O) and it's the O (oxygen atom) that is needed in the Retro-Brite process. In general, the more O, the better.
So how do we get more free radicals?
Turns out hydrogen peroxide decomposes faster when exposed to heat and light. They are also two cheap ways to decompose it. We prefer light because it’s easy, free if you use the sun, and you often times get and added benefit of slightly elevated temperatures. As these oxygen radicals are produced they serve as the active component that reverses the yellowing and institutes a new chromophore configuration. More on that in the next post!
This begs the question, would peroxide work by itself, without heat or light?
Technically yes, but because many peroxides (especially those purchased off the shelf) have stabilizers in them, they don’t break down quickly. However, they will break down slowly, but it just may many days/weeks to produce the desired effects. So we recommend sticking with adding light/heat
There's also another question lingering -- what wavelength works best for decomposing peroxide?
The shorter the wavelength the better the peroxide absorbs and decomposes peroxide (also called the "Molecular Extinction Coefficient" or MEC). Most black lights are ~395 nm's (UV-A) and they do work for Retro-Britening. This wavelength has a MEC of 0.00066 liters/mole.cm. However, the shorter the wavelength the better (another great article here and here). UV-B has a range of 280-315nm (and corresponding MEC btween ~4.2 to ~0.2). UV-C's wavelength ranges from 100-280 nm and it's MEC ranges (>140 to 4.2nm). So, based on this metric the shorter the wavelength the better it is for Retro-Britening. We recommend a UV-C type of light with wavelengths shorter than 280 nm. I hope to complete some experiments with this parameter in future posts and videos!
Next we will dig a little deeper into what happens to the radicals.
If you have questions, comments, or feedback on this post or any others, please email us at support@www.retro-brite.com. We'd love to hear from you!
Part 1: How Retro-Brite Works: Into/Summary
Part 2: How Retro-Brite Works: Understanding Oxidation Potential
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