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Thread: Remove yellowing from plastic using just the sun - and nothing else??

  1. #1

    Default Remove yellowing from plastic using just the sun - and nothing else??

    I just recently discovered this video by Retro Recipes - using just the sun, no chemicals, to whiten yellowed plastic in just a day or two.



    I've tried it for a couple days and so far it seems to work! I have two Apple IIc computers and two Victor 9000 keyboards and I put the more yellowed one of each in the sun for an entire day. Both ended up looking whiter than the previously less yellow ones. (I would have taken before & after photos, but I was too excited to get started.. and frankly, too damn lazy)

    Seagull checking out keyboard.jpg
    (seagull seems to approve)

  2. #2
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    Hmmm, I wonder if UVC would have a more pronounced effect. I've got a small faceplate that I'll leave in an EPROM eraser for a couple of hours. That'd be interesting.

  3. #3
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    It does work, just very slowly, and some items react much better than others. Here in Georgia I have to be careful things don't melt when it gets 100 degrees F and up and it doesn't rain. About 3-4 days takes most of the bad yellow out leaving just a little classic "patina".

    I'd be interested to know if UVC has the same bleaching effect as the sun...

  4. #4
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    What I would really like to see is some honest to goodness side-by-side scientific comparisons of different methods.

    There are a lot of variables to consider, such as exact material makeup (usually unknown), temperatures, actual sun/uv exposure received, how yellowed the material is to start with, if it is yellowed all the way through, and a lot of different things to measure such as brittleness after exposure, how deep did the whitening get, and so on.

  5. #5
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    It'd be great if someone with access to a Hunter colorimeter could measure color before and after exposure. The Hunter measure yellowness (a), blueness (b) and luminosity (L). There are handheld units that could measure the surface of a component down to about a half inch diameter.

  6. #6

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    Quote Originally Posted by rittwage View Post
    It does work, just very slowly, and some items react much better than others. Here in Georgia I have to be careful things don't melt when it gets 100 degrees F and up and it doesn't rain.
    Yes, I think it's best not to let the plastic get too hot.

    I've had perfect weather: 23˚C, sunny all day, cool ocean breeze. The plastic never got more than slightly warm to the touch.

  7. #7
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    Tried to de-yellow a bit of plastic with my EPROM eraser; uses a germicidal tube with plenty of UVC (you can smell the ozone). After three hours, nothing. Curiously, the plastic insides of my eraser have yellowed from exposure to the UV; the outsides look pristine. Maybe that's not the answer.

    I'll stick in the sunshine tomorrow--highs are supposed to be in the low 80F range.

  8. #8

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    Interesting. UVC is blocked by the atmosphere, isn't it? If so then it couldn't be the UVC that is causing it to whiten in the sun. I assumed it was the UVB that helps whiten it.

    This Apple IIc was nearly as yellow as a banana. It's still not perfect, but I'll try another couple days in the sun.
    Apple IIc.JPG
    Last edited by Mr.Amiga500; July 12th, 2019 at 03:47 AM.

  9. #9
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    Some near-UVC does get through the atmosphere, although not a lot. I thought it might be worth a shot. So that leaves us UVA (mostly) and UVB.

    I did find this paper on the effects of UV on bleaching of paper. UVA-to-near-UVB seems to be the active agent there. Note also, when it comes to newsprint, UV causes yellowing, depending on wavelength. The bleaching effect seems to be centered around 400 nm.

    More grist for your mill.

  10. #10

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    Although, UV bleaches the surface, I understand that it also exposes the surface to greater oxidation, later. I think we also need to look at how fast the plastic ages to yellow again.
    Also, does it just turn the outer surface in a chalky white that rubs off easily?
    Dwight

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