Yellowing: the Plastic Equivalent of a Sunburn

Your fancy white electronic brick of consumer electronics started off white, but after some time it yellowed and became brittle. This shouldn’t have happened; plastic is supposed to last forever. It turns out that plastic enclosures are vulnerable to the same things as skin, and the effects are similar. When they are stared at by the sun, the damage is done even though it might not be visible to you for quite some time.

Photodegradation

Photodegradation is nature’s way of saying you should be playing more video games indoors instead of being outside. The process is complicated and full of interesting chemistry, but the gist is that the sun puts out a lot of UV radiation, which results in the breaking of the plastic polymer chains and formation of free radicals. Free radicals are atoms or molecules with unpaired electrons that are highly reactive.

Even if the plastic is put away in a box in the basement for a long time, exposure to the sun before boxing can have damaging effects that will cause the material to yellow while in the box. You can see the white keys on this keyboard have turned a sickly yellow since it was taken out of service a decade ago.

Color fade is also a result of UV radiation breaking down the chemical bonds in the dyes. The dye works because its chemical structure reflects only certain wavelengths of light, so when that structure is destroyed, it no longer reflects light the same way.

Photodegradation is a term that refers to the cause, not the effect. Light is doing damage, and not just to color. By breaking down the plastic polymer chains, it’s making the plastic more brittle. This affects PVC pipes and many kinds of rope, and susceptibility to UV radiation should be considered when choosing a material for outdoor use, especially when it’s a rope that is supporting a person.

Just like with other chemical reactions, heat and pressure can speed up the degradation, so even the process of making the plastic can initiate some of the damage that will happen later.

UV stabilizers; the Industry Sunscreen

Plastics manufacturers try to combat this effect by putting in additives. These UV stabilizers delay the harmful effects of UV light. The top three UV stabilizers are UV absorbers, quenchers, and HALS, and they are all appropriate for different stages of the photodegradation process. The UV absorber takes the bullets for the plastic, and instead of breaking down it converts it into heat or IR radiation and dissipates it through the polymer matrix. There are lots of UV absorbers, depending on the material and color of the plastic (carbon black is a popular one, but doesn’t work for white or clear plastics). Quenchers are more like doctors in the sense that they save molecules that have been hit with UV light before they can break down. HALS, or Hindered Amine Light Stabilizers, are policemen; they trap free radicals so they can’t do any damage.

It’s common to use all three types of stabilizers in a plastic, but they will only delay the photodegradation. Eventually enough exposure will overwhelm the absorbers, quenchers, and HALS, and the plastic will lose its color and become brittle.

Fire Retardants

This is another class of additives to plastics, and is another reason why they can yellow over time. One common fire retardant additive is bromine, which is great at keeping the plastic from burning, but not so great at resistance to UV light. The bromine breaks down and becomes free radicals, which then bonds to oxygen. Over time, the bromine migrates towards the surface and the yellowing gets even worse.

As an aside, you shouldn’t laser cut fire retardant plastics because the bromine in it is a halogen that is bad for people and machinery.

Fixing it

The bad news is that color fade and embrittlement are permanent and can’t be fixed. The good news is that the degradation happens from the outside in, so the yellowing may just be on the surface. For yellowing, there is a technique called retr0brite that has proven successful, and essentially involves using MORE UV light to break apart the bromine-oxygen bonds. Hydrogen peroxide is then used to get in there and fill the broken bonds with hydrogen, making the bromine more stable and reversing the yellowing. Unfortunately, the retr0brite page seems to be disabled, but it can still be accessed through archive.org for more details.

Preventing it

Use only plastics without flame retardant additives, stay away from all windows, and keep your plastic shielded from any source of UV radiation. Or just go about your business and accept that over time, UV radiation destroys everything, including our loved ones, whether they are human or plastic.

58 thoughts on “Yellowing: the Plastic Equivalent of a Sunburn

    1. He uses some sort of thicker hair peroxide that works quite well.
      This already has some sort of thickening agent.
      The trick is of course with a C64 case, remove all electronic parts,
      the case halves HAVE to be super clean, or the plastic will have a marbled effect because of dirt etc.
      Then use rubbing alchahol scrub with a brush and cloth very well.
      Then apply the retrobright with a paintbrush. The 8-bit guy uses plastic wrap
      apply it on the plastic working out air bubbles, I guess this helps keep the retrobright where it belongs. I have heard some say using the plastic wrap is not a good idea, up to the individual though.
      If you live in an area that has this hair peroxide, hair dressers use this, but Dave discovered this does work.

    1. He mentions not being able to find large zip-lock bags but I’m surprised he didn’t try vacuum storage bags as they can be huge.
      While technically they’re designed to keep air out – given the ozone generator has an output air-tube – he could just feed the output pipe into the bag and let the valve (normally used to suck the air out of) to keep a limited positive pressure so the bag remains inflated (plus it ensures a that ozone levels are topped-up)

        1. Some brimstone baritone Anticyclone rolling stone Preacher from the east
          Says, “Dethrone the dictaphone.Hit it in its funny bone. That’s where they expect it least.”

          And some new mown chaperone Was standing in the corner Watching the young girls dance
          And some fresh-sown moonstone Was messing with his frozen zone Reminding him of romance

  1. Ive whitened a Apple Lisa just by putting the case parts outside in the sun and rain for a week. but the methode with peroxide and uv is easier and faster. I would use a uv light source though so i can do it indoors. But then i would not have the added heat by the sun.

  2. Plastic degradation caused by sunlight is really not reversible and anything you might do just further changes the plastic. The best answer is to protect anything you value from UV radiation, not just from sunlight but other light sources too.

  3. Yellowing plastic is one thing, but the one that’s really annoying is that horrible ‘soft effect’ plastic that turns into a gummy mush after a few years. My 3D0 welded itself to a carpet (plastic feet), and headphones, mice and toasters have all fallen prey too…

    1. Yes, this rubber coating is a plague: it dissolves with human sebum and create a sticky goo.
      Manufacturers should put an end to any surface treatment with plastic (paint, chrome, etc) leave the plastic solid it will last longer.

      1. Paint or chrome is not that bad, when it wears off there is just plain plastic under it. But this rubbery stuff is really a pest. I don’t think it has to do much with fat (sebum). I think it is an oxidation process. Especially rarely used parts seem to suffer most from the degradation. E.g. a rotary knob on a radio controlled clock/weather station. First this knob is bad design, it activates just a contact when turned 90° – why not put another button on the front between the 10 others. But obviously some designer found it looking cool. You need it only when you want to set the clock manually or enter a “Zone” for the correct calculation of dawn and sunset. So you just use it twice a year – or not at all if you don’t care about this “zone”. And suddenly after 5 or 10 years it got sticky.
        A ear/nose hair trimmer also is covered with this shit. It is really rarely used and has it’s first or 2nd AA battery in it, but it got sticky after 5 – 10 yrs. I dusted it with talcum powder to fight the stickiness. :-)

        This rubber should really get forbidden, it’s a “good” example for planned obsolescence.

    2. This.

      The buttons on some iCom ham rigs (IC-821 in my case) are made out of that stuff. I’ve had success by removing the elastomer sheet entirely and cleaning it with isopropanol. Works great, doesn’t seem to do any harm. I’ve also gotten good at re-seating the connector that goes to the front panel, too. It hangs down, so vibration eventually dislodges it. The whole front panel is a goof-up, but the rest of the radio is pretty good.

      1. I’ve heard the same complaint regarding the Yaesu VX8-DR. I had one that was in good condition, until it drowned in a thunderstorm (yes, it is a submersible, go figure) and I sold it for $20 as parts.

        The new owner couldn’t recover it, but did find its battery still held a good charge and all the rubber plastic bits were in good condition which helped replaced the gummy bits his VX8 had.

    3. My Bluetooth mouse had that crap on it. It was annoying me every time I used it until I taped over it.

      Why don’t they just use silicone instead if they really want it soft?

      1. Probably because silicone is no thermoplastic. This crap is also known as TPR, thermoplastic rubber, so it can be injection molded. Silicone or real rubber have to cure by chemical reactions, this takes longer. But that’s no excuse, better leave the soft stuff out completely if there is no good solution. Or make a slightly rough or knurled or otherwise structured surface if it’s a rotary knob or has to give good grip even when wet.

    4. Depending on the type of rubber they’ve used and at what temperature the plastic carrier starts to permanently deform at:

      I’ve boiled some of those in hot water to somewhat “revulcanize” the rubber.
      Sometimes when it is a flat sheet of the stuff then I’d clean down the rubber (Using cyclohexane/label-remover) to rid it of lint and make the stuff thin,
      then I press cyclohexane soaked paper larger than the area onto the surface to give it that matte effect,
      leave it 15 to 20 minutes,
      rinse the paper back with Isopropyl for a few washes (Reclaimed Isopropyl is OK for a few reclaims),
      peel the paper off carefully and then boil the panel.

      I’ve restored the iconic rubber coated IBM/Lenovo LCD-lids on said brand laptops using this method,
      also had a sticky mouse-pad buttons with 3mm thick degraded rubber (Some last-gen C2D era HP Elitebook),
      Took a knife blade and some Cyclohexane to flatten the buttons and reshape them,
      Soaked them in Isopropyl to temporarily make them hardened and non-stick for rolling on a sheet of paper,
      left them in a bucket of boiled water until the water cooled down to put my hand in and pull out the now restored buttons.

    5. I have this same issue with my 2008 BMW, the passenger side pull is this soft sticky mess while everything else is perfect. People don’t usually ride with me, but when they do it always comes up.

  4. Want to see UV damage occur in real time? Just place an unopened bottle of coke out in the sun and check on it every day. You’ll see the coke slowly turn completely clear as the UV from sunlight breaks down the caramel coloring!

    1. interesting! I wonder if it’s still “safe” to drink at that point.

      what if this is where Crystal Pepsi came from? some fool left a pallet of it out in the sun at the bottling plant and to keep from getting fired, spun it off as a new product idea.

  5. That picture looks very similar to my logitech keyboard that went yellow pretty fast too. At the time, i was thinking it might have something to do with me smoking in the room where the keyboard was, or my dirty fingers… Guess they just messed up at the factory when mixing the plastics. And yes, the keys really are less UV resistant than the rest of the keyboard case and get more discoloration.

    1. Haha, I was about to post the same thing – “wait, I HAVE that keyboard.”

      What’s weird though is mine was always in a keyboard drawer at work, out of direct light and it still turned brown like in the photo above. I just chalked it up to too many cheetos but now I wonder if like you’re saying the plastic formulation was just hyper-sensitive to aging or something.

      Just a fun memory from my past. I should dig around and see if I still have it somewhere… hehe.

  6. Super Nintendo anyone? Apparently, Nintendo got a few batches of fire retardant that turned out to be very prone to the yellowing effect. So some SNES consoles will turn yellow almost before your eyes, but others won’t. And some consoles have parts with and parts without the offending fire retardant. The latter category is by far the worst looking :)

  7. It’s really something that will vary greatly based on the type of plastic and whether the device maker cheaped out on the case or not.

    Look at white vinyl windows and siding. Or white plastic eavestrough and related bits. That stuff stays white for a couple of decades or longer.

    1. Windows are normally PVC. This probably does not need extra fire retardant as PVC contains so much chlorine (60% wgt) that it is normally self extinguishing without any additives.
      And there are some electronic devices where parts of the casing (upper shell, lower shell) which appear to be the same plastic when new, are yellowing very different. So there are differences in the batches.

  8. This is a big problem in piano-organ keyboards. A reason to keep the cover down or use a towel. If all yellowed even, but there is a often a shadow of the sharps leaving white areas. An ivory tint isn’t bad here. Instead one or two notes at all octaves turn worse than all the others, caused by different amounts of dope on different production runs.

  9. My close friend tried to clean his SNES by using hair care products. He stopped into a salon while in his work truck and asked for the product. Little did he know it was used to make meth. He later that day had the state cops at his house.

    1. If I need normal H2O2 (for pool treatment) we just buy that, 30% stuff in 10l cans. I used this also for making PCBs. I only bought the hair care peroxide when I really bleached my hair over several years.
      But I know of a problem in Germany 10 or 20yrs ago when lots of electronic hobbyists who bought hydrochloric acid, hydrogen peroxide and acetone via mail order had the police showing up and in some cases even confiscated a “white powder” in the kitchen (which would have tasted sweet or salty). They were accused of manufacturing explosives.
      When I first used the HCl/H2O2 method for PCB etching and acetone to remove the photo resist I did not know that ordering this chemicals together would become suspicious some years later.

  10. Maybe it’s just that I’ve been watching it and its brethren degrade slowly over the decades, but all my Model M keyboards clean up with just household cleaners. None seems particularly yellow, or at least any more yellow than each other. In fact, not at all.

    1. This is true! we have a machine at my work that is turning yellower and yellower as the time goes by. you wouldn’t think it at first, but when I moved a magnet that was stuck to the side, you can see the original beige color under where the magnet was. this machine has been inside, away from any window for it’s entire 7 years since we bought it new.

  11. Can one make an argument for just leaving old things looking old? Of course there’s horrible examples like the one pictured above, but I firmly believe that old things are allowed to look old. I shudder when “collectors” just retrobrite the shit out of anything that comes with just the slightest hint of coloration, often to the point where they look brighter than the originals. To me that’s the equivalent of magazines photoshopping models’ teeth to rgb(255,255,255).

  12. I’ve found the most effective method is to use laundry whitener dissolved in a tub of warm water. Make sure the whitener has sodium percarbonate as its active ingredient. When water is added, this becomes hydrogen peroxide. The item to be whitened is then completely submerged in the mixture and placed in the sun. You may need to weigh it down.

    I believe this gives far more even results than painting on the mixture or covering with cling wrap. When I have had uneven results, it’s most likely a result of the plastic already being damaged. This was proven when I had an item which had a sticker which I removed before treatment. After treatment, I found the area not covered by the sticker was chalky.

    More details here: http://members.iinet.net.au/~davem2/overclock/Retrobrite.html

  13. Another yellowing source is gas stoves- everybody seems to love them cause they think it’s best to pretend their on Hell’s Kitchen- but then fail to install and/or use their outside ducted vent hood to keep the combustion products out of their homes.

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