Guide to removing yellowing of plastics

[Merlin]

Does that mean you may give it a try as well, tonyyeb?

I'm not 100% sure, but somewhere like Holland & Barratt in the UK may stock xanthan gum. It's food safe, so health food stores may stock it.

[tonyyeb]

So what would the process be? I will certainly give it a go. I have an A1200 keyboard that wants the treatment!

[Merlin]

OK,

What I've told Lorne to try is to prepare your peroxide solution, then as soon as you have added the Oxy, follow it up immediately with the xanthan gum. the xanthan gum is a powder and it may take a bit of stirring to get it to dissolve (think like preparing wallpaper paste).

My best guess as to how much to add is about 1/4 teaspoon per pint (1.5 grammes per 500ml or about 0.25%), we are aiming for a mobile gel that can be brushable. You shouldn't need more than 1/2 teaspoonful, unless you plan to walk on the surface of it!!

[Anemos]

Good guide
I approve the idea of Hydrogen Peroxide, and I propose addition 10% of clear alcohol in the final mixture (this will make the mixture more drastic).
Edit:also, I believe that with increase of temperature 30~35C roughly the results will be still faster and drastic..
and for you make the mix in form gel, (if I understood well), you can it added in water few cooking gelatin

[gklinger]

Originally Posted by Anemos

I approve the idea of Hydrogen Peroxide, and I propose addition 10% of clear alcohol in the final mixture (this will make the mixture more drastic).

You're saying that adding isopropyl alcohol will accelerate the process?

I believe that with increase of temperature 30~35C roughly the results will be still faster and drastic..

Wait, what do you mean by drastic?

[Anemos]

i mean(ethyl alcohol),
and drastic = more powerful

[gklinger]

Originally Posted by Anemos

i mean(ethyl alcohol),
and drastic = more powerful

Thanks for the clarification. I'm not a chemist so I want to make sure I'm clear on what is being suggested. More powerful means it will do its work more quickly, right? I'm still trying to wrap my brain around the fact that you can't over do this process because the plastic goes back to its original colour. I'm reminded of the time my girlfriend came home complaining that the hairdresser had used too strong of a solution or left it in too long and her hair ended up, well, lets say not the colour she had hoped for.

[Merlin]

@ gklinger

The simple science is... the UV light breaks the bond between the bromine and the oxygen because the UV light is exactly the right wavelength to do that and it's a quirk of bromine that the Br2 molecule can be split by UV light. The oxygen gets replaced by a hydrogen from the catalysed peroxide and this is what reverts the plastic to it's original colour.

Once you have replaced all of the oxygens which were attached to the bromines in the flame retardant, that's all she wrote; the reaction slows down and stops, because there's nothing left to sustain it, unless you put fresh parts in to be treated. It's a bit like fastening a zip, eventually you get to the end.

@ Anemos

Would you care to explain your reasoning behind the use of alcohol? I am intrigued, how would this accelerate the process? Have you actually tried this or is this just a theory?

EDIT: I have been thinking about this all morning and have discussed it with my esteemed colleague Zetr0.

Our feeling is that mixing alcohol and peroxide with a catalyst like TAED present may be steering us towards rocket fuel country and the risk of fire etc. Due to this, I am loathe to take this idea forward; our process is fail-safe at the moment and adding alcohol is adding risk in my opinion.

[Merlin]

The gel version of our magic brew works!! Lorne over at VCF added some xanthan gum to our magic brew and tested it on a panel, photos are here at the end of the thread:-

http://www.vintage-computer.com/vcfo...ed=1#post72305

Yes, I know these are long threads, but this reflects the interest and amount of work being put into our discovery.

Fan-tastic!!!

[Merlin]

The thread over at VCF is over 200 posts long now and getting to be a heavy read for some, so Lorne and I thought it was best that we start a new thread at VCF and put an update on here, with a "Story So Far" summary, before we start more experiments.

So, what has been discovered and learned so far?

1. We have learned that a magic concoction has been created that can reverse the years of yellowing of plastics, caused by the brominated flame retardants (which were added to the plastic when it was a masterbatch) migrating to the surface of the plastic and attracting oxygen molecules which become attached by a co-ordinate bond.

2. Bromine molecules are susceptible to ultra-violet light, in that chemical bonds involving bromine molecules can become destabilised if irradiated by UV light. This is what we are exploiting to remove the oxygen molecule from the brominated flame retardant.

3. The yellowing can be reversed to a degree by immersing parts in hydrogen peroxide or "Oxy" on their own, however, on their own they don't do that much; what is needed is a chemical called TAED (tetra acetyl ethylene diamine), which is a chemical found in the "Oxy" type laundry boosters. Why is this useful? It's useful because it catalyses perborates and percarbonates in the "Oxy" to produce peroxides; it can also catalyse hydrogen peroxide, which is exactly what we want. This is what makes the mixture much more potent.

4. The optimum mixture and conditions for reversing yellowing of plastics seems to be the following:-

A) Hydrogen peroxide solution, the strongest you can lay hands on;
B) UV light, either as sunlight or a UV lamp;
C) Approx 1/4 teaspoonful per gallon of "Oxy" laundry booster.

Parts immersed in this mixture will have the yellowing reversed in six to eight hours on average. Severe yellowing may take longer but it will only be a matter of a day or two. The mixture once made will last about four days before all of the peroxide is spent.

5. A more recent development is that the mixture can be made into a gel. Initial tests with Xanthan Gum added to the original mixture have shown that it can be made into a thicker material which can be brushed onto surfaces. This mixture foams up but still removes the yellowing when put under UV light, and can remove yellowing in four to six hours. This method also drastically cuts down on the amount of liquid required and means large areas can be treated at a relatively low cost. Other thickeners such as corn starch, hydroxy ethyl cellulose, wallpaper paste, latex or similar inert thickener may also work, however, tests are in the early stages, feel free to try some of these and report back if they work.

6. Recent tests by Lorne have shown that powdered hair bleach and hydrogen peroxide solution can give a similar effect to the original "Oxy" mixture, however, there may be side effects associated with using this material; early tests have seen adverse effects on paint and stickers may also be affected by this product. The original "Oxy" mixture does not affect paint or stickers, unless the stickers are held on with a water based glue or are paper stickers.

7. If you are planning to do this in a hot climate, please be aware that this mixture will heat up during the day. Lorne is in Arizona and found that temperatures in excess of 100F (38C) and beyond were encountered, which caused some warping and distortion of large pieces. If this is the case where you live, always add the component to a cold mixture and check the temperature during the day.

We will add to this original post in the threads here and at VCF as we learn more.

The story continues.........

[tonyyeb]

Isnt this thread sticky yet?

[Zetr0]

@Tonyyeb

to be honest, I think jope is hibernating

(either that or tooo much beer and pizza.... which is easily done btw)

he needs to conserve his strength for the spring when all those naughty little random post whores come out to play, posting random meaningless stuf in threads

[Merlin]

Perhaps I need to add some Xanthan Gum to this thread... LOL

[Chain]

my attempt with most yellowed kb



30% peroxide only, took 7 days (in almost dark place)

[tonyyeb]

Hmmmm, I wonder which keys you did?!?!

[Methanoid]

@tonyyeb - great post - can I ask how one safely removes keys - is it just prise them off or is there some trick to it?

[Jope]

Prise them off gently if you want to do a quick job.

The safest way is to dismantle the base plate and poke them out from underneath.

[Specksynder]

All my A500 keys are now white, it seems like a new old stock Amiga
That's amazing

@rkauer, Merlin : Thank you guys!

[Supamax]

@tonyyeb:

Hi, I would like/need to use a UV bulb as you did... (I saw it in your first post in this thread)
Which type would I need? Fluorescent? How many Watts?

Have you an eBay "sample" link to a bulb similar to the one you used?