I suspect a lot of these electronics are intended for indoor use and are not made of UV stabilized plastics. I'd rather have yellowed electronics than ones made brittle by being left outside in the sun.
Most yellowed plastics are likely brittle too.
How plastic can rust, sort of
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Re: How plastic can rust, sort of
#12I've never heard of setting plastic out in the Sun to reverse yellowing. UV light is overall pretty terrible for plastic, as it will become brittle and break down. It will eventually turn to dust from UV exposure alone. So if you care about the longevity of the plastic and not just its cosmetics, don't do the sunlight thing.
Re: How plastic can rust, sort of
#138-bit Guy does this frequently in his restorations.[1] He’s tested a lot of methods in the past. [2] One thing I noticed in the old video is that heat worked even better than sunlight in the peroxide solution, and the sunlight was also heating the water in the Texas sun. But the light makes a difference as seen by the rock shadows. He’s also built indoor UV setups before. He didn’t seem to be aware of sous vide immersion heaters as a solution for making larger volumes of heated water at a stable temperature since he was thinking of inventing his own version of one with various parts from the hardware store.
[1] skip to 2:45 https://youtu.be/xhBnyK5lQ2s
Re: How plastic can rust, sort of
#14I've only heard of retr0bright in this regard. SNES consoles are pretty famous for yellowing at different rates. As other commenters have stated, sunlight degrades plastic. It may perform some whitening, but you're damaging the old electronics.
Re: How plastic can rust, sort of
#15This is done with Lego bricks as well. It may weaken the plastic to some degree. For larger pieces of plastic it shouldn't be a problem though.
Re: How plastic can rust, sort of
#16I wonder how hydrogen peroxide (a strong oxidant) can reverse the yellowing of plastics, if the yellowing is the result of oxidation. I'm not a chemist, but this doesn't seem to make sense.
I'd guess it strips away a thin layer of plastic to reveal the non-yellowed plastic underneath.
Unfortunately retrobriting doesn't take off surface dirt or ink or similar. Painting-like surface preparation is required beforehand. Just dumping sort-of-casually clean parts in the solution will lead to splotchiness and areas that don't get cleaned. The official site recommends a gentle dishwasher cycle, I've had luck with that.
In a way, its good it works that way. It doesn't strip off the apple logo or "mac" lettering or whatever.
Your theory is reasonable but it seems its actually breaking down a bromine based fire retardant. Bromine itself is kinda gross brown color and some oxides like dibromine pentoxide are clearish-white so its quite realistic that hitting it with an oxidizer clears things up.
Re: How plastic can rust, sort of
#17This is done with Lego bricks as well. It may weaken the plastic to some degree. For larger pieces of plastic it shouldn't be a problem though.
I remember reading about using Brasso to de-yellow LEGO but I've never tried it myself.
Re: How plastic can rust, sort of
#18I see the retrobright community as pure OCD.
Just leave it as it is. Yellow is cooler. It shows vintage class.
Re: How plastic can rust, sort of
#19I suspect a lot of these electronics are intended for indoor use and are not made of UV stabilized plastics. I'd rather have yellowed electronics than ones made brittle by being left outside in the sun.
Observationally heat seems to make plastics more brittle than sunlight. Top of dash car parts seem about as brittle as shaded bottom of dash car parts.
Field service people seem to kill laptops in a couple years, although we're talking about hours long process not years so that shouldn't matter, anyway I don't recall the exposed tops of their laptops being worse than the bottoms of their laptops.
The scientific debate about plastic breakdown seems to be over centuries vs thousands of years exposures so mere hours will be fine.
https://phys.org/news/2019-10-sunlight-degrades-polystyrene-...
Re: How plastic can rust, sort of
#20I wonder how hydrogen peroxide (a strong oxidant) can reverse the yellowing of plastics, if the yellowing is the result of oxidation. I'm not a chemist, but this doesn't seem to make sense.
If you follow some links in the OP you can end up at a source article[1] that has some comments on the actual chemical processes occurring for both the discolouration and reversal (Ctrl-F "bromine").
TL;DR: Over time the bromine based flame retardants in retro-era plastics degrade (hence the yellow/brown colour) and H2O2 plus some energy (UV light/heat) can be used to reverse the process.