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     Ok, I need some help with my yellowing problem. I got a bunch of old LEGO Bricks second hand, and a whole bunch were yellowed. So what I did, was take them and put them in a bin for around a month. When I finally got to fixing them, I used 3% hydrogen peroxide and set them out for around 3 - 4 hours. The whites did perfect. The transparents did not. They had a very orange tint to them, and still do at the writing of this. So if anyone can help me figure out this issue, it would be greatly appreciated. Thanks in advance!

                                          -legostarwars1425

P.S.

Some of the parts are cloudy too.

If you can help with that, that also 

would be greatly appreciated.

Thanks again!

Edited by legostarwars1425

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@legostarwars1425

Is the cloudiness just the transparent parts? If so and if the cloudiness is caused by scratches that are not individually visible to the naked eye, you can reduce the cloudiness with Pledge Multi-Surface Wax (formally, Klear). Make sure the parts are clean and coat the cloudy areas with an extremely thin coating of Pledge. Treat it as you would varnish. Allow it to dry for 24 hours and, if necessary, apply another extremely thin coat and allow that to dry. It's very important that the coats are thin. This doesn't work on opaque (ABS) parts.  

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On March 15, 2018 at 8:16 AM, AmperZand said:

@legostarwars1425

Is the cloudiness just the transparent parts? If so and if the cloudiness is caused by scratches that are not individually visible to the naked eye, you can reduce the cloudiness with Pledge Multi-Surface Wax (formally, Klear). Make sure the parts are clean and coat the cloudy areas with an extremely thin coating of Pledge. Treat it as you would varnish. Allow it to dry for 24 hours and, if necessary, apply another extremely thin coat and allow that to dry. It's very important that the coats are thin. This doesn't work on opaque (ABS) parts.  

Yes, the cloudiness is only in the transparent parts, and I'll make sure to try the Pledge Multi-surface Wax. Thank you so much! 

Edited by legostarwars1425

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3 hours ago, legostarwars1425 said:

Yes, the cloudiness is only in the transparent parts, and I will make sure to try the Pledge Multi-surface Wax. Thank you so much! 

No problem. I should have mentioned that the cloudiness may be caused by micro-abrasions on both sides. You can tell by either looking at the piece close-up from a very oblique angle or by touch. If by touch, you'll need to wash the part with soap and water and then dry it before applying the Pledge. Some people say you should allow the Pledge to dry with the part horizontal and the Pledge side up in which case, you'll need to apply the Pledge one side at a time. Others say that because you're applying such thin coats, it won't run so you can do both sides at once and allow the part to dry vertically. I favour the horizontal, i.e. one side at a time approach, but maybe because I'm overly cautious. 

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On March 15, 2018 at 9:51 PM, AmperZand said:

No problem. I should have mentioned that the cloudiness may be caused by micro-abrasions on both sides. You can tell by either looking at the piece close-up from a very oblique angle or by touch. If by touch, you'll need to wash the part with soap and water and then dry it before applying the Pledge. Some people say you should allow the Pledge to dry with the part horizontal and the Pledge side up in which case, you'll need to apply the Pledge one side at a time. Others say that because you're applying such thin coats, it won't run so you can do both sides at once and allow the part to dry vertically. I favour the horizontal, i.e. one side at a time approach, but maybe because I'm overly cautious. 

Thanks you so much! I'll try one side at a time. Thanks for the extra advice!

 

 

 

 

Edited by legostarwars1425

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When I tried to retrobrite (the hydrogen peroxide solution) clear LEGO (notably macaroni bricks - which are very expensive), I felt like the solution softened the plastic... the frist time I took one out and wiped it dry with a paper towel (I just wanted to see how it did, I normally put them out on a towel after rinsing and let them air-dry), the effects were horrifying.  I tried allowing other ones to air dry, but it just never came out well.

At the same time, I haven't tried it with the retrobrite+oxyclean method (that was way back before I heard about adding an oxidizer).  If you haven't added an oxidizer, it might also be the case that you just didn't leave them long enough.  The peroxide only solution can take all day, especially at only 3% strength (and you certainly shouldn't further dilute it, if that's what you're starting with).

I did a fair sized batch yesterday and was disappointed that only around 1/3 of my whites actually were white at the end; I had to redo the rest today - I started as early as I could and only just took them in a little while ago (around 6pm).  They were out there at least eight hours, and with oxyclean, and while the vast majority look great, there are still a couple of pieces that are yellowed.  This isn't my first rodeo, either, I've had a lot of success in the past, but never had pieces this stubborn.  Time to start a filler bin.  But the point is that you may need to just give it a bit more time.

 

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Last year I whitened 4 white (well, tan) 6192's because those are bloody expensive.

It worked pretty well, they got very white. But interestingly, 3 of them were stored in a room that only see the light a few hours per month (otherwise pitch black), and the fourth one stored in a drawer. A year later, they are all 4 back to full tan.
Meaning: it doesn't last, and it doesn't seem to yellow again because of light at all. They got back to tan where they originally where (in the first place because of light exposure), not in their back.

Also, peroxide goes off, this second time I tried to use it, zero bubble, all off, no effect. Meaning that I'm now reconsidering if this is really worth it, if you have to constantly bother to whiten the parts, and re-buy peroxide afterwards.
This also tells me that it'd be quite wrong for a seller to whitened parts, I hope no one does.

That being said, has anyone's experience been different? Perhaps a longer exposure in peroxide makes them stay white for longer?

Edited by anothergol

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Oxyclean is a percarbonate salt (i.e., instead of a hydrate, it is a hydrogen peroxidate).  Thus, you're really just generating H2O2 in situ when using Oxyclean, so if you think you are not applying an oxidizer, you are.  However, there are several advantages to Oxyclean:

1. As a solid, it does not degrade on storage like liquid solutions of H2O2.  Thus, using a scoop of Oxyclean now will be the same as using it next year, and thus you don't have to worry about degradation (i.e., 'going off', as noted by anothergol).

2. The carbonate portion of the salt is basic.  This may or may not help with what you are trying to do.

3. You can add more Oxyclean to concentrate the hydrogen peroxide solution higher than standard 3% solutions in a bottle.

As for yellowing of clears, isn't the clear a polycarbonate?  Or were they polycarbonates back in the day?  Most of the bricks should be ABS, but I believe that the transparents are polycarbonate and I have never seen it in print, but I suspect that the trees are probably polyethylene or polypropylene (based on their soft texture).  I think there are some rubbery parts, too (spear tips, some minifigure items), and am not sure what the polymer is.

In any case, the standard yellowing is thought to be due to the brominated flame retardants that used to be put into the ABS bricks.  These would break down over time and leach the brownish decomp products into the polymer, leaving the 'yellowed' look.  This can be destroyed by the free radical oxygen caused by the action of UV light on hydrogen peroxide (thus the leaving the H2O2 solution out in the sun).  This solution only presents itself on the surface, however, and more of the additive will diffuse through the polymer over time, thus leaving the yellowed color again despite being protected from light.  I suspect that the decomposition is thermal rather than light catalyzed, or at least thermal with a light activated chain reaction, and thus it will yellow when stored away from light.  I suspect if you cleaned up a white brick with the H2O2, then put it in your freezer, it would keep white much, much longer than if you left it out at room temperature.

The next question is: How do you clean up clear polycarbonate bricks?  One needs to understand the mechanism of discoloration.  If it is due to surface abrasion, then polishing the surface again would help.  If it is due to diffusion of polymer additives over time, then the nature of this additive must be understood to discern a method of clean up.  Off the top of my head, I don't know what the difference is in flame retardants and plasticizers between ABS and PC.

PDF with list of ABS additives for those who are interested:

http://icl-ip.com/wp-content/uploads/2012/01/ABSGnlICLIP.pdf

Edited by Grover
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Finally explained in a clear concise manner that makes sense, instead of some voodoo witch doctor hope and pray potion. Thanks @Grover for taking the time to properly explain it.

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You're welcome!  Being an organic chemist rarely comes in handy outside of work. lol  BTW, if you want to research this yellowing, the polymer term for plasticizers and flame retardants leaching and yellowing is usually called 'bloom' in the industry.  If I have some free time, I may see if I can figure out what flame retardants are used in PC.

I kind of want to try extracting the flame retardant in a Soxhlet and running NMR on it to see if I can identify it.

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On 6/27/2018 at 6:58 PM, Grover said:

the standard yellowing is thought to be due to the brominated flame retardants that used to be put into the ABS bricks

Do you know when Lego stopped btw? (that is, how old a part has to be for it to be a worry)

 

I've found this article that also warns about using Oxy with colored parts. http://blobblubblobblog.blogspot.com/2016/03/undoing-yellowing-on-abs-plastic-like.html

Here I wouldn't even dare to use Oxy, mainly because I can't be sure that these brands/products are exactly the same in all countries.
That is, I have used the "Future" floor wax trick to restore scratched tranparent parts. Here it's called Pledge, but the problem is that the product is different than the one generally used, instead of being clear it's opaque tan. I've ruined pretty much half of the (already useless anyway) parts I tried it on. While it did have a serious effect on the transparency & shine, it left crap looking like candle wax, that just couldn't be removed anymore. I believe the clear version most likely leaves the same thing, only it's clear & much less a problem.

Edited by anothergol

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Even though I have not been out of my dark age long enough to have yellowing issues or scratched trans clear parts I still have read enough about it to realize it's an issue. I do wonder if anyone has ever tried some of those automotive headlight lens cleaning kits on their trans clear parts, they seem to work miracles on TV with polycarbonate lens. 

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That's a great link to some good experimental work, anothergol!  I took a look, and there are several versions of oxyclean, some with and some without detergent, and even some in liquid form.  It may be that some of that is causing issues with the dyes.  Of course, it could be that the dyes themselves are incompatible with strong oxidizing agents.  Personally, I would not use the hair salon peroxides as described in the article, for the same reasons as using the Oxyclean--it could have surfactants or other chemicals that could ruin the dyes of the bricks.

As to your question, I do not know when they stopped, if they stopped, or what flame retardants they were using and are now using.  There are definitely flame retardants in the bricks, though, or they would light on fire without provocation.  I suspect that there are environmental, suspect carcinogenic, and cost reasons associated with their choices.

Johnny1360, I thought about those headlight kits as well.  I have not tried them, but I am very curious if someone does, as they do appear to work well on the headlights.

I took a look through flame retardants on polycarbonate, and it appears that one is tetrabromobisphenol A (TBPA).  Not sure if Lego ever used this or not, but it is a blooming flame retardant that has been gradually phased out over the years, and is also susceptible to free radical reaction, so could be cleaned up by peroxide.

Based on this mechanism, I suspect that yellowed pieces could be cleared up by UV light and application of any commercial product with a radical initiator, such as acne cream containing benzoyl peroxide in sufficient concentration, or chemicals like AIBN.  Not that lab chemicals are commonly available, but it would be an interesting theory to test.  Also makes me wonder if mild radical producing oxidizers like NCS would be useful.

Edited by Grover

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About trans part yellowing, though: I've only seen bad cases of yellowing on these old parts in trans clear, so far:

lego-transparent-windscreen-2-x-4-x-2-38

But they are still in production & cost absolutely nothing, so if someone ever gets a yellowed one, it makes no sense to bother with it. Bricks are also (obviously) very old, but same thing here.

Old canopies that have become very rare are trans-yellow ones, and well, they're already yellow, so..
And the major problem with old canopies is scratches, anyway.

The only yellowed trans-clear parts I ever got were 3464.png.

But the OP said they were Star Wars sets, so they couldn't be that old. So I suppose that parts don't have to be that old to yellow. I can understand it's a problem for SW's printed canopies.

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So, to add to this, I also ended up with some transparent 2 x 4 parts from the early sixties that were in better condition. With the old logo and everything. When you compare the two of the same piece ... ouch. I have much work ahead of me.

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15 hours ago, legostarwars1425 said:

So, to add to this, I also ended up with some transparent 2 x 4 parts from the early sixties that were in better condition. With the old logo and everything. When you compare the two of the same piece ... ouch. I have much work ahead of me.

You haven't said which part(s) it was, though.

Surely if you bother they're rare parts?

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On 6/29/2018 at 8:13 PM, anothergol said:

Here I wouldn't even dare to use Oxy, mainly because I can't be sure that these brands/products are exactly the same in all countries.
That is, I have used the "Future" floor wax trick to restore scratched tranparent parts. Here it's called Pledge, but the problem is that the product is different than the one generally used, instead of being clear it's opaque tan. I've ruined pretty much half of the (already useless anyway) parts I tried it on. While it did have a serious effect on the transparency & shine, it left crap looking like candle wax, that just couldn't be removed anymore. I believe the clear version most likely leaves the same thing, only it's clear & much less a problem.

It's Pledge where I am too and slightly brown when poured out, but I haven't had the problems you describe. It sounds like you applied it too thickly. The coat has to be really thin and only works for scratches that cause cloudiness, not ones that can be traced with the human eye. 

As for ABS parts, I whitened some yellowing second hand white parts in 2014 using Vanish Oxy Action Crystal White powder, hydrogen peroxide and sunlight. Since then, I have kept the parts in the dark at room temperature and none of them show any sign of yellowing. At the time of writing (2018), they are indistinguishable from new white parts I bought back in 2014 to which they have been assembled.    

Edited by AmperZand

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35 minutes ago, AmperZand said:

It's Pledge where I am too and slightly brown when poured out, but I haven't had the problems you describe. It sounds like you applied it too thickly. The coat has to be really thin and only works for scratches that cause cloudiness, not ones that can be traced with the human eye. 

The thing is that it worked for the parts that didn't have too much sharp bits, for those the liquid dropped nicely, for the others it stacked in places and hardened there. For those angular parts, there was no angle I could hang them at that would have let the liquid pour out everywhere.
And even where it worked, it wasn't that amazing. I had old classic space canopies from my childhood, they went from nearly opaque to semi-transparent, which is ok - I wasn't expecting miracles anyway.

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On 6/30/2018 at 8:00 AM, Grover said:

As to your question, I do not know when they stopped, if they stopped, or what flame retardants they were using and are now using.  There are definitely flame retardants in the bricks, though, or they would light on fire without provocation.  I suspect that there are environmental, suspect carcinogenic, and cost reasons associated with their choices.

Is it possible to determine type of flame retardants used in bricks experimentally? To understand if new bricks are affected by same yellowing issues like the old ones.

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Yes, you can figure out what the flame retardants are, but it is not easily done at home unless you live in an analytical chemistry lab.  Usually analytical labs charge a lot of $$ for this, as this service is typically called deformulation and is used to reverse engineer competitors' products.  From a practical standpoint, you would start with an educated guess as to what the most common flame retardants are, or simply a collection of all the flame retardants that were commercially available during the time period that you're interested in.  Then there are a number of ways to go, and this list is by no means all inclusive:

* Examine the properties of these materials and ideally you will find a solvent that will not dissolve the ABS but will dissolve the flame retardants, even a little bit.  For example, ABS is much more soluble in ketones, esters, and polar ethers like THF than it is in say methanol or ethanol.  If you find a flame retardant that is soluble in one of these alcohols, you can extract the flame retardant with it, usually via something like a Soxhlet extraction.  Then you collect and concentrate the extract and analyze it, typically by 1H and 13C NMR, IR, and MS.  If you can get enough material by this method and you have correct solubilities, this is probably the most definitive method.  This becomes complicated by the colorants in the system (i.e., blue, red, whatever color dye).

* If your flame retardants have the same solubility as ABS, or you can't separate them from the colorant, then you can look at thermally degrading the material in a closed system and collecting the gasses.  In some cases, you can get volatilization of the flame retardant, allowing it to be analyzed in trace amounts in equipment like a GC-MS and you can hopefully compare the molecular ion peak to the molecular weights of the suspected flame retardants.

* You can also dissolve the entire ABS sample in something like MEK, filter out as much of the gelled/swollen polymer as possible, then inject the solution onto an HPLC or LC-MS.  This separates the various compounds by polarity, so you will be able to see how many components you have, usually a UV-VIS spectrum, and the parent ion mass (except in the case of the polymer, which is more complicated, but we already know it's ABS, so we don't really care).  Compare this data to that of the pure flame retardants you're looking for and you will hopefully get your answer.  This unfortunately requires a lot of time working up a method for the LC that works to separate the materials.

* I would suggest that an ATR-IR probe would be able to see the bloom and help ID the yellowing agent, but I doubt the agent is thick enough (this usually requires a few micron thickness).

The main problem with any of these methods is that the instruments are pretty expensive (the NMR for instance, is usually around $400k or more, and the 'cheap' instruments, like a benchtop IR, start around $15k), and the methods are time intensive.  No company is going to pay for the time on these instruments and workers time to do the bench work to look for trace amounts of a flame retardant, unless they are a competitor, and in that case, they'd likely keep their results to themselves.  The best we can hope for is that we find a university student with access to these resources and some curiosity--maybe an undergraduate project could do this, or a graduate student studying flame retardants in polymers...

Probably way more detail than you wanted. :classic:

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That's a cool way of saying NO :wink: To be honest I read all of it and, while I didn't really understand the whole stuff, it was interesting to read. I was hoping there is a way of throwing bricks into some chemicals and get some results based on reaction. Oh well, hopefully we'll find some students interested in brick chemistry.

Speaking of students, there was one, long time ago, who studied Technic bricks strength for some his work in University and later shared the results. So there is a chance, we just need to find one interested both in chemistry and LEGO!

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I have 3 questions for @Grover

1) I have some yellowed pieces of many colors from set produced between 2005 and 2010 and i've noticed that the treatment with just 3% h2o2 and sun works properly only on white and old gray pieces while the other colors fade, also the fading appears only where the brick was originally yellowed but leaves the rest of the brick's color unchanged: do you know why it happens? is it the reaction with the h2o2 that turns the color lighter or it just reveals the true color that has been changed by the sunlight?

2) If the bromine is the problem, would it be possible to just wash it away? I've googled it and found this -> https://www.ncbi.nlm.nih.gov/m/pubmed/22575175/?i=2&from=/22236948/related is it useful for our lego?

3)Are the yellowed bricks dangerous/poisonous in any way differently from brand new bricks? And what about retrobrighted ones?

Thanks in advance

Edited by TheLegomane

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There may not be easy answers to all your questions, but I will do my best.

1. Usually the yellowing comes from bloom (aka leaching) of the flame retardant out of the brick; this may or may not be the case with every generation of brick.  Such a reaction can be in reaction to external stimuli, such as UV light (usually the sun), heat, or something else.  Thus, if you have a brick that was part of a wall, the UV could have hit it only one side, yellowing only that side.  Hydrogen peroxide breaks down into radicals when hit with UV light, and it is these free radicals that then react with brominated (or other halogenated or labile functional groups) flame retardants to remove them.  Again, this assumes that the flame retardants are the source of the yellowing and further that they are halogenated.  Unless there are such functional groups on the colorants themselves (red, blue, green whatever), those shouldn't react in the same manner (although hydrogen peroxide is an oxidizer, so they could react with it in this capacity).  If TLG changed additives, these could react in different ways with the retrobrighting process.  In order to understand what was happening, you'd have to have TLG's formulations from the different time periods and examine the chemical additives individually for reactivity.

2. Ideally, yes, you should be able to wash away the brominated contaminants.  Sad to say, solubilities make this nearly impossible, for the solvents such as the alcohols that you saw in the paper you linked to will dissolve (at least partially) or swell the ABS itself, ruining the bricks.  So yes, it will remove the brominated materials, but it will destroy the bricks in the process.

3. One can't say one way or the other about the dangers of the older vs. newer bricks.  In order to do so, you'd have to know what the original formulations were over the years for each brick and color, and then you'd have to be lucky enough to find studies that had been conducted on the carcinogenicity of each of these.  The formulations are probably TLG proprietary, and the carcinogenic studies are fraught with questions, whether genuine or cooked up by industry trying to discredit them to keep selling their product, and thus you then have to sort all that out as well.  As for those that have been 'retrobrighted', it's again difficult to say.  They could leach faster or slower than untreated bricks, and there are no studies to my knowledge of the effects of retrobrighting on the structural integrity and porosity of the bricks.  It could be that they bloom less or more, or that a whole new plasticizer/emulsifier/flame retardant/oligomer/etc. could be leached.  The best guess you could make would be to take a look at studies done on ABS bloom from various decades (if indeed something like that has been done) and then hope that TLG used something along those lines in their formulations.

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Damn everytime you post @Grover I feel like I actually learn something. Thanks for the concise and informative post, it's good to hear about this stuff from someone who knows what they're talking about. 

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@Grover Thanks for your answer. 
I understood the first 2 parts but, sorry, not the third.
I just wanted to know if a yellowed brick is more dangerous for health than a brand new brick (even for a kid)
Thanks in advance

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