or: How I learned to stop worrying and love my plastic
This is going to be a simple summary of the techniques used to revert yellowed plastic cases back to their original colour. Rules:
- Simple and concise. If you want to read more, the sources and the rest of the study material are linked below.
- Written from the point of view of the average person who is trying to fix a plastic case: what works, what doesn’t, how difficult and dangerous the process is and for how long it’s expected to last.
- If you read “maybe” or “possibly” in a phrase then it’s an educated guess, but it has not been fully tested/proven yet. Common sense applies to fill the gaps.
- This is a work in progress. I will gladly accept more suggestions and corrections accompanied by data and reports in order to make the list more complete and accurate.
- All credit goes to the people who did the research and other analysis before me. I’m only trying to put the information together in a way that’s easier to read.
- Also it goes without saying -but I’ll say it anyway for obvious reasons-: be careful with what you do! Wear appropriate protection, don’t splash bleach in your eyes, don’t drink it, don’t spray paint your face even if it sounds funny, don’t wear your good clothes.
|Method||Hydrogen peroxyde bleaching (Retrobrite)||Chlorine bleaching||Sun bleaching (Lightbrite/Sunbrite)||Paint||Wash & Scrub|
|Danger to you||Hydrogen peroxyde can be harmful, make sure you follow the recommended precautions when handling it.||VERY DANGEROUS! Chlorine kills very easily if you don’t know what you’re doing. In short: don’t do it.||If you *really* want to stare at it until it’s done, apply some sunscreen and you should survive.||Little, as long as you use proper breathing mask and eye protection, plus doing it in a well ventilated area.||Don’t drink soapy water and you’ll be fine.|
|Danger to the plastic parts||Hydrogen peroxyde bleaching is slightly more harmful than Lightbrite, but less harmful than chlorine.||Chlorine bleaching damages your plastic more than any other method.||Any kind of bleaching will damage the plastic. Sun bleaching is the least damaging compared to the other types of bleaching.||Make sure you use paint designed for use on plastic and apply it correctly. If things go wrong, paint can be stripped and re-applied. Only method that will make your case structurally stronger.||As long as you use a mild detergent and gentle scrubber there’s very little risk of damaging the plastic.|
|Danger to the internal components||Hydrogen peroxyde will damage circuit boards and components.||Chlorine will SEVERELY DAMAGE any electronic or mechanical component.||Sun exposure, condensation, rain can all SEVERELY DAMAGE any internal component. Do not leave your machine out in the sun without taking it apart and storing away the internals safely!||Paint can cause damage to mechanical parts, plus may damage some electronic components such as potentiometers.||No damage to internal components IF POWER IS NOT APPLIED while the board is wet. Make sure everything is properly dry and it will be fine.|
|Time required||Medium/Long: likely 1 or more days, but may have to be repeated.||Short/Medium: bleaches in minutes, but takes time to prepare everything beforehand||Long: couple of days to a week to get some consistent results.||Medium/Long: it will require some preparation and the paint needs to dry.||Very short: you take apart the machine, wash the case, dry it up, reassemble. Done.|
|Equipment needed||Hydrogen peroxyde (liquid or cream), plus suitable containers and some basic protection. Easy to find.||Most checmical involved are not easy to find and the procedure requires specialized tools and extensive preparation.||Common household tools to disassemble the machine. You may need a rotating plate to achieve good results.||Needs paint and personal protection. Most hardware stores sell all that’s needed.||Common household stuff|
|Skill needed||Medium: if the process is not done properly it can lead to “marbling”, so it requires some practice and experimentation.||Very high: handling dangerous chemicals is not something you should do unless you are trained and experienced.||Just enough to be able to disassemble your machine and put it back together.||Medium: painting takes some practice, but once you do you can get some pretty good results.||As long as you take care in taking the machine apart and putting it back together, it’s very simple.|
|Expected results||If done correctly it can bring the colour close to the original one. Reports and some educated guessing say plastic will become yellow again over time (one year, maybe more?)||The bleaching is very pronounced and care needs to be taken for it not to “bleach too much”. Yellowing will return after some time.||The bleaching effect will be more or less pronounced depending on how long the plastic is left under the sun. Some early results, plus educated guess, says it will go back to yellow in a short amount of time (months).||A proper paint job will not only look very nice, but is the only method (so far) able to reinforce the plastic structurally, making it last longer. Also it’s reversible if you change your mind.||If your case has not been cleaned in a while, you will likely see some results. It will vary based on where the machine was stored, if someone was smoking, etc.|
Other random useful bits:
- Bromine (used a flame retardant in ABS plastics) does not cause yellowing, it’s a common misconception.
- The yellowing process is due to the plastic itself slowly changing chemical composition. It will also make the plastic brittle over time and there’s no known way to stop it 100%.
- The process can be started by heat and/or UV light. The UV light influences it more than heat does.
- The ABS degradation that occurs at normal operating temperatures (around 40C) is not the same as the one occurring when higher heat is applied (80C and above). The low temperature process, over time, will affect the entirety of the plastic, while a high temperature degradation usually occurs on a thin layer on the surface.
- A very good explanation of the situation by David Flood https://medium.com/@pueojit/a-look-into-the-yellowing-and-deyellowing-of-abs-plastics-db14b646e0ad
- A Quora answer by Josh Velson, also cited by David Flood in his explanation, with more details: https://www.quora.com/What-is-happening-in-terms-of-a-chemical-process-when-hydrogen-peroxide-is-used-to-restore-discoloured-Lego
- A paper on photodegratation of ABS plastic: https://www.researchgate.net/publication/242293723_PHOTODEGRADATION_OF_ABS_FOR_TECHNOLOGICAL_APPLICATIONS_INFLUENCE_OF_HINDERED_AMINE_STABILIZERS_HALS_AND_ULTRAVIOLET_ABSORBERS_UVA_ON_COPOLYMER_STABILIZATION
- Mechanics of polymer photodegradation: https://books.google.co.uk/books?dq=photodegradation+of+abs&hl=en&id=0MTrCAAAQBAJ&lpg=PA243&ots=UlOPjtvG6w&pg=PA243&sa=X&sig=TijhksIHSxiQ1tNLiVTZLywJ1Hk&source=bl&redir_esc=y#v=onepage&q=photodegradation%20of%20abs&f=false
- Thermal degradation of ABS blends: https://www.sciencedirect.com/science/article/pii/S0141391002000459
- Video of a chlorine bleaching solution affecting various plastic components: https://youtu.be/9J4yF3OpYZQ
- A study by James E. Pickett on reversibility of yellowing in plastic polymers: https://www.researchgate.net/publication/278721049_Reversible_post-exposure_yellowing_of_weathered_polymers and https://drive.google.com/file/d/1vE41ASE14kZVGjEFz_tsiLRLK3c928Eh/view
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