What Makes Plastic Turn Yellow? Hint: Sunscreen Won’t Help

Cruising through that mega-auction website, you just saw someone paid several hundred dollars for aOld TV, yellow plastic (now) antique video game console. Remembering you have one just like it, you dig out the box from the back of the closet and examine the game. All the parts are there, and it even works when you plug it in. There’s just one big problem that could affect the game’s value in the eyes of potential collectors — the once-white casing is now a dingy, unattractive yellow.

What happened?

Plastic’s longevity is one of the qualities that makes it such a useful material — and one of the reasons why we try to keep it out of landfills and waterways. Most plastics (polymers) are pretty stable and durable. But plastic isn’t perfect. Over time, it can change color (which is what happened to your game console) or become brittle.

When either effect occurs, it can change the way the plastic behaves in real life, and the product made from the polymer may no longer do what it was intended to. Those plastic bubble skylights from the 1970s were a good example of this effect — with age, the plastic turned yellow and the skylights leaked!

A couple of years ago, the Polymer Solutions team investigated a situation in which polyurethane Accelerated UV testing can be used to identify points of failure in polymers. medical tubing, designed to be clear, turned yellow and failed well before it should have. Since part of the tubing was meant to remain outside the patient’s body, the discoloration and failure were particularly worrisome. In other applications, failure of a medical device could even be life-threatening.

Polymers can have problems for a number of reasons, but when the trouble involves a color change, UV exposure is one of the first suspects we examine. The ultra-violet spectrum of light doesn’t play well with most polymers — unless, of course, you add light stabilizers, but we’ll get to that in a moment. Exposure to UV radiation can cause plastics to change color (turn yellow), crack, break, shatter or even melt! We have multiple analytical techniques that can determine if UV exposure has caused changes in a polymer, one of which is accelerated UV testing.

The testing helps us understand if a polymer or plastic is absorbing too much UV, and make suggestions for additives that can address the problem. Depending on the issue and the intended use of the polymer, the manufacturer may add a UV-absorbing stabilizer, a quencher or HALS, which trap free radicals formed by exposure to UV radiation and prevent them from causing damage.

Of course, UV radiation isn’t the only factor that can cause plastics and polymers to age. Exposure to visible light, extreme temperatures, humidity or exposure to solvents can also cause a polymer to fail over time. When it comes to yellowing, however, UV light is often the primary culprit.

Getting back to your game console, it probably sat atop your TV for years — catching some rays — before you packed it away. Even though it’s been sitting in darkness for a while, the damage was already done and yellowing occurred. UV radiation was also the source of the yellowing in the case of the medical tubing failure. It turns out the patient was an avid sunbather, so the tubing got a much higher dose of UV rays than the manufacturer anticipated.

23 Comments


  1. I was disappointed that this article did not mention the formation of dimer quinones from hindered phenols at all. A major oversight in my opinion.

    Reply

    1. Hi Dr. Hauger,

      Thanks for reaching out & bringing up a way to improve this article. It can be challenging keeping things succinct within a blog post yet also diving deep into the science. You bring up a great point and worthy topic for discussion. We welcome a guest blog on the topic from you or someone at your firm. You are welcome to email me directly at caitlyn(dot)scaggs(at)polymersolutions(dot)com if there is interest on your end.

      Best wishes,

      Caitlyn Scaggs
      Polymer Solutions

      Reply

  2. Whatabout the defects and harmfulness of your (UV-absorbing stabilizer, or other substances added) to human and nature?

    Reply

    1. Hi,

      Thanks for reading the article and reaching out! You raise a good point. It is always important to evaluate the safety of a product both to people as well as wildlife and the environment. There are guidelines established by regulatory bodies for a wide variety of substances and products–and analytical labs like ours help ensure the products are adhering to those requirements.

      Please let us know if you have any additional feedback or comments. We hope you will continue reading our blog and interacting.

      Best wishes,

      Caitlyn

      Reply

  3. This article was written in a manner I understood and even without any prior knowledge, I can now explain to my customers why their conservatory roofs are be coming discoloured.
    Thankyou.

    Reply

  4. I have a split A/C and the plastic on the interior part has turned yellow. but the plastic has never been exposed to direct sunlight.
    Is there anything else other than UV that can cause this yellowing? and more importantly how can i restore it to its original white without hindering the plastic’s integrity?
    Thank you

    Reply

  5. This was a very informative article, and it was written in aa simplified way that is easily understood. I’ve been on oxygen for several years, I routinely change the clear tubing each week, however, my oxygen tubing has started to turn a green color and not the yellow mentioned and shown in the article.

    Besides having been on oxygen for a several years as well as being bed ridden…the chances of UV light is minimal due to the disease I have and the need for a more darkened area verses my retul

    This is certainly a new, strange as well as somewhat worrying discovery and I would really appreciate some help as it’s actually concerning me. (Just FYI, I haven’t switched manufacturer, style or anything. I also do not use a humidifier bottle having never been able to keep water out of the line despite trying everything on the market).

    Thank You!
    Diana

    Reply

    1. Hi Diana,
      We are so glad you found this article beneficial. I suggest contacting the manufacturer and letting them know you are experiencing this issue.
      Best wishes,
      Amanda, Polymer Solutions Incorporated

      Reply

  6. Similar to Tal, I’ve seen Polyurethane pellet (thus, still pellet form, not yet processed further into parts) that turns yellow even inside the packaging Gaylord box. I work for a company that is in difficult situation now, where some 10 tons inventory of polyurethane pellet all turn yellow, and they all are still in the wrapping plastic liner inside packaging box from the supplier. Those boxes are stored indoor where humidity is kept low and temperature is kept cool 7/24. I doubt if in this case UV Light is the culprit since Gaylor box would have prevented any UV light to get in.

    Any idea, what else might cause the yellowing for the stored PU pellets? Thanks.

    Regards,

    Radi-

    Reply

  7. Just bought a data cable(white color) a couple of weeks ago. Now the color has turned to brownish. Any idea why?

    Reply

  8. I understand the whole concept of the UV rays turning plastic yellow, but in my case it does nothing to answer my querry. My sewing machine has been protected in it’s original packaging (styrofoam and cardboard box for years. It’s only been in the last 9 months that it’s gone from nice white to a dark yellow. It was also kept in the camper where there are no lights. So what gives?? Your article was good, but it certainly doesn’t apply to me. Please help explain my machine.

    Reply

    1. Hi Jo-An,
      It’s very likely related to the stabilizer package used in the plastic. There is a mechanism called “gas fading” that can occur in the stabilizer. This can happen if the plastic is exposed to NOx gases from the combustion of natural gas, propane, car exhaust, etc.
      We don’t know if this is happening, but a quick change to yellow without exposure to light or heat would lead us to think it’s related to the stabilizer package. It’s likely not going to impact the physical properties much in the short term.
      Sometimes exposure to direct sunlight for a few hours can actually reverse gas-fading color. I hope this helps!
      Best wishes,
      Amanda
      PSI Blog Team

      Reply

  9. Can the thinner paint make plastic turn yellow?
    I have an air conditioner installed in the bed room and its plastic cover turn to yellow after renovating my room with the paint thinner.

    Reply

    1. Hi Tony,
      Great question! You are welcome to email info@polymersolutions.com to discuss your question in more detail.
      Best wishes,
      Amanda, PSI Blog Team

      Reply

  10. Yes this was a very helpful topic and does explain a lot.
    I am a collector of Vintage and antique mowers as well as old Vacuums,and what I’d like to know is.Is there anyway of fixing this discolouring and making the plastic look fresh and new again?
    Thanks.
    Jeffrey

    Reply

    1. Hi Jeffrey,
      We are so glad you found this article helpful! You are welcome to email info@polymersolutions.com to discuss your question in more detail.
      Best wishes,
      Amanda, PSI Blog Team

      Reply

    2. You can reverse the yellowing of plastics with a product called retrobrite or using peroxide if the part is small. I would do a quick search of these methods and see if they work for you. The 8-bit guy on youtube has some informative videos on the subject as well.

      Reply

  11. I don’t have a reply but I do have a question. Is there anything that can be added to morphing and it friendly plastic that would help the clolor maintain for a longer amount of time and what about the plastic that is not in the sun at all but still turns yellow?

    Reply

    1. Hi Laurie,
      Thank you for reaching out! You are welcome to email info@polymersolutions.com to discuss your question in more detail.
      Best wishes,
      Amanda, PSI Blog Team

      Reply

  12. Spending a couple years in Thailand I have witnessed plastics deteriorating faster than normal. The pollution index is 4 times higher than Florida, where I now reside. Since the two areas share the same climate — I wonder why things go ‘bad’ quicker in the Land of Smiles? I’m wondering if the pollution is so high in Bangkok that the air carries a high content of petroleum — as plastics crumble and thinly rubberized materials turn to a sticky goo before their normal lifespan? I can only imagine that people breath in this stuff!

    Reply

  13. My garden tub in my mobile home has turned yellow, I am looking for answers to how to clean it. Any ideas?

    Reply

    1. Hi Sylvia,
      Thank you for reaching out! Spraying the tub with hydrogen peroxide may remove the yellow stains.
      I hope this helps!
      Best wishes,
      Amanda, SGS PSI Blog Team

      Reply

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