New method using just Sunlight?!

Jespher

New Member
May 31, 2019
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So I joined this forum to let The 8-Bit Guy know about this video that You-Tube recommended to me after watching his latest Restoration video with the DOS compatible Commodores. I watched it all the way through and I think it's worth a shot.
Channel name is Retro Recipes
Video is titled "Incredible Retrobrighting Discovery Deyellow with just Sun? No bleach/dismantling. Read FAQ!"
here's a link to the research paper mentioned in the video and also linked in the video description
Reversible post-exposure yellowing of weathered polymers *Edited link to include name of research paper

Also on his channel there was this video Commodore Music Maker Refurb - The Beginning
If you could find one of the Commodore Music Makers it would make a great crossover with your 8-Bit Keys channel.

Edit - well I feel a bit embarrassed now, apparently they know each other. Well I'll leave it up since its still a really interesting discovery that 8-Bit Guy probably helped with.
 
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HornsOverIthaca

New Member
Jun 2, 2019
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Yes, it's true. I was able to get this to work on a yellowed SNES, browned plastic from a broken C64, and the space bar from an old apple keyboard. Days have been cloudy recently so I can't really say how long it takes. I left them all outside in direct sunlight for about two weeks. I plan to try it on the exterior plastic of my PowerMac8500 next. I haven't tried this on non-disassembled components yet.
 

rhubarb

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Jun 4, 2019
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I'm to understand this method seriously degrades the plastics. I can't say as I haven't tried it, but I would be nervous about putting my baby out in the sun.
 
May 22, 2019
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Short version is that UV causes chemical reactions that break down the polymer chains that make plastic... plastic. So you need a stabilizing agent. This is usually a pigment that absorbs the light and converts it to heat, rather than interacting with the chemical bonds that hold the polymer chains together.

UV light breaks down polymer chains, which damages plastics. It also breaks down the chemical bonds in whatever is discoloring the plastic, which is why it tends to whiten... so it seems to me that the challenge is to break down the "yellowing" without damaging the ABS.

The thing is, every piece of equipment is different. It has a different history, has been exposed to different environments, and may even be a different chemical composition than other equipment. The shell of my Commodore 128 is not the same as my breadbin 64 - which is obvious by the color alone. So we can't expect exactly the same results from two different pieces of plastic left in the sun.

This is why anecdotal evidence is so inconsistent - one person says his plastic is still looking good a year later, while another person says his is brittle and looks worse than it did before he whitened it. However, we don't know the composition of the plastic in question or what, specifically, is making it yellowed. (This can be different with different plastics.) Without the same starting conditions, two people will get two different results, and one person's vintage gear can be improved while another person's is simply ruined after sun bleaching.
 
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Jespher

New Member
May 31, 2019
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Before writing off this method take a look at the research paper I'll link again here, Reversible post-exposure yellowing of weathered polymers
this is a 2004 published study from GE Global Research its also available on www.sciencedirect.com

The study used multiple samples of differing levels of degradation. All samples of each "grade" were exposed to the same amount of weathering. This effect was observed in all sample "grades" so its not anecdotal. I will admit, and so does the paper, that there is still some permanent damage to the polymers stability, but this is mostly an effect of the already present weathering. Also remember quite a few retrobrite recipes tell you to put the HydrogenPeroxide covered plastic in the sun or box with UV lights for better results, typically for the same amount of time that this calls for. For me its woth the risk, put it out for 5-6 hours and see the results.

Now obviously if you have a severely degraded piece of plastic any method of retrobrite has a risk of destroying the piece. So know your piece's history as best you can and try at your own risk.