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De-Yellowing plastic - the stain isn't permanent after all

cleaning plastic de-yellowing peroxide experiment

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#1 Orpheus

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Posted 10 July 2009 - 08:03 PM

We've all had plastics that have yellowed and won't wash clean. Sometimes it's just a pale gray mouse or keyboard slowly going beige; sometimes it looks like a severe "nicotine staining" and we assume there must be a smoker in that household (I've known nonsmokers to overestimate the satanic evils of smoking, since smokers rarely "lit up" in their homes, yet the stains were all over the house, and quite dark.) A white plastic chassis may turn such a dark brown in hot spots that you may be certain it must be burning, and may even discard it. The staining can often spell the difference between a treasured collector's item or conversation piece and worthless junk. It's not uncommon for perfectly functioning household items to be replaced because they are dingy and ugly: organizers with once-clear plastic drawers, lawn furniture, kitchen appliances... anything visitors might see.

Many of you may have suspected it wasn't environmental, but rather "aging". I've had items that yellowed while sealed in plastic inside never-opened factory original boxes, and identical plastics exposed to identical conditions may differ greatly in yellowing: Most of us have seen two-toned chassis where the top and bottom were dramatically different colors after as little as a year. Game consoles, computers and other electronics devices that get warm are particularly prone to this.

It turns out this yellowing is usually the result of bromine released from flame retardants added in the master batch to facilitate production and later molding. (Bromine, you will recall is a dark reddish brown liquid at room temperature) The loss of bromine doesn't necessarily mean that the plastic itself is deteriorated or unable to give decades of further performance, though a mental illusion often convinces us they feel brittle or rough.

It turns out to be relatively easy to remove these stains with common household materials. You may be surprised how "factory new" some items feel after deyellowing. More than once, I've been surprised, because I'd come to believe an item had been beige to start with, but the cleaning (and internal surfaces) reveal that it was originally white or gray.

ESSENTIAL CONCEPTS
I'm not going to get too deep into the chemistry (which actually dips into quantum mechanics), but I want to make it clear what we are *not* doing. Though the key chemicals are often used as bleaches and cleaners, the process is not bleaching the plastic or removing dirt. It's just mobilizing the bromine, which has migrated to the surface, and forms a stable complex with atmospheric oxygen. (Note that the bromine didn't stain the full thickness of plastic upon manufacture.)

The second key point is that ultraviolet light is CRITICAL to the process. The UV is what actually mobilizes the bromine -- just as heat and UV often contribute strongly to plastic yellowing, but mobilizing the bromine to the surface in the first place. If you use the solution alone, you may not get appreciable effect from soaking plastics for weeks in you basement. Since you only need a day or so of direct sun (or the equivalent in UV lamp or indirect shaded sun), you won't damage the plastic

Stronger is *not* necessarily better. We're really trying to *limit* the reaction, so ther eaction only reacts with the UV-activated bromine (the easy target) reacts, not the plastic. The plastic is much more resistant, but there's thousands or millions of times as much plastic as bromine present.

Daylight UV isn't a problems --these plastics are designed to stand up to sunlight for much more than a day-- but too-strong UV lamps, too much heat (the rate of the undesired side reactions doubles with every 10C rise in temperature), high peroxide concentrations, too much activator (creating too many free radicals), too long an exposure (after most of the bromine but gone) or letting the cleaner completely dry -- all of these may slightly overclean or even damage the surface. I'd suggest keeping the peroxide under 20% or more: 6% (20 volume) works fairly well (and you don't really need gloves) and even 12% is still pretty mild (and is unlikely to react dangerously with many of the incompatible substances on the MSDS warning). Then, if you see just a wee bit more stain that you want to knock off, try a brief UV session (maybe 30 minutes) at high peroxide concentration.

I originally encountered this idea in a blog entry by someone who restored *deeply* yellowed (actually brown) old game consoles and computers by soaking the cases in big plastic trays full of hydrogen peroxide (and a few other chemicals) on their back porch. I was impressed by the results, but it seemed expensive (and rather a hassle) to fill those  big containers with chemicals, especially here in New England, where the weather might not cooperate. Who wants to bring big, heavy, sloshy trays of strong chemicals out of the rain, and store them inside the house?

However, the process seems to work equally well if you mix a smaller batch, add a thickener, and simply brush it on. If one activating chemical is lect out of the mixture, it can be stored for weeks, to be activated and brushed on as needed. The objects can be left out if it starts to rain, and rebrushed when the sun comes out. It's easier than painting.

THE RECIPE
500 ml (1 pt) Hydrogen Peroxide(H2O2) diluted to 6-12% (20-40 volumes)
While 3% (10-volume) drugstore peroxide can work, it may take many days of UV exposure. Further, since it is borderline to start with, it may not last very long: you may need a new batch each day. Finally, since hydrogen peroxide breaks down to oxygen and water, the stuff in your bathroom (or store) may be substantially less than the stated 3%. ("10 Volume" means that 1 volume of solution will release 10 volumes of oxygen gas. You could easily jury-rig a measurement test, using, say, a dab of manganese dioxide paste from inside a dead dry-cell or alkaline battery as a catalyst)

For quicker, and likely better, results, use a stronger hydrogen peroxide. I'm personally happy with 6-12%, but some go up to the strongest that is easily obtainable e.g. probably Prochem Urine Rescue, available at many custodial or carpet cleaning suppliers (~$20/gal) or pet supply retailers (Petco, Petsmart) for ~$30/gal. It's about 30-32% or "100 volume". Beauty supply shops (like Sally Beauty in the US/Mex/EUR/JAP) sell hair bleaching peroxide up to at least 40 volume (12%) for a few bucks a pint, but you should examine the ingredients. Avoid any with Terpene (which can eat plastic) and generally avoid organic compounds (crudely: anything whose name doesn't trace to ammonia or the periodic table) with one exception: Tetra Acetyl Ethylene Diamine (see below). If it comes premixed in the peroxide (vs. in a separate packet), your deyellowing solution won't last as long in storage.

To dilute peroxide: initial concentration * initial volume = final concentration * final volume
e.g. 30% * 1L = 6% * 5L, so add 4L water to 1L 30% peroxide solution to get 5L 6% peroxide

Though home use peroxides of over 6% should come with warnings enough, I feel obligated to say:

WARNING: Read the MSDS. Hydrogen peroxide is a strong oxidizer and corrosive to skin, eyes, lungs (if inhaled directly), clothing and wood products. It may react violently with some substances, including acids, bases, metals, metal salts, reducing agents, organic compounds, flammable substances. ONLY USE CLEAN GLASS OR PLASTIC CONTAINERS AND UTENSILS AND PROPER SAFETY GEAR (e.g. gloves and goggles). A dab of the black paste found inside a dead flashlight battery, dispersed in some water, will catalyze hydrogen peroxide to oxygen and water for disposal. Add it carefully/sparingly to avoid splatter/boilover of unreacted peroxide.

2.5-5cc (1/2-1 tsp) Oxy-Clean powder (activator)
This contains a small amount of Tetra Acetyl Ethylene Diamine (TAED) which acts as a catalyst for the hydrogen peroxide in our deyellowing solution. Oxy-clean also has perborates and perchlorates (which is what the TAED is *meant* to catalize) These may add a little something to the deyellowing process, but I never bothered to compare it with pure TAED.

Food Thickener (optional, only use for paste form)
I suggest food thickeners beause they are cheap, available, and shouldn't contain any incompatible contaminants that react with peroxide. I suggest making a roux, slurry or cooking the thickener to paste, as you would with food, before adding peroxide. NEVER heat anything containing hydrogen peroxide on your stove. Make a thick goo, cool, then mix it with the peroxide. I use a magnetic stirrer to avoid putting metal in contact with peroxide, but many report using hand or kitchen blenders to mix the peroxide paste, over months of experiments, so I guess steel, especially stainless, must be okay. I definitely wouldn't even think about an aluminum blade or pan.

Arrowroot, flour, cornstarch, potato starch, xanthan gum, CMC/carboxymethylcellulose, guar gum or food thickeners sold to help older people swallow all work, and are available in grocery or health food stores. I use Xanthan gum, because I bought a big bag for food experiments, but found it a bit slimy for my tastes. A few mil of glycerine really helps Xanthan thicken up.

Proper use
You can dilute the peroxide and mix with thickener weeks in advance. Always store peroxide and its mixtures in a cool dark place in a glass or plastic container, but not on a wood shelf or on paper liner. It may slowly decompose to water and oxygen, especially if the container isn't scrupulously clean. Don't cap it so tightly that it will burst from internal pressure if you forget it.

Set up a place to "sun" the plastic object all day. You can hang it from strongs over a plastic tray to expose all sides, or just lay it down yellow side up. If possible, arrange a loose transparent cover to prevent drying. Make sure pets, children, stupid friends, etc., can't get at it. The reaction will work, but more slowly, in a shaded location with good exposure to clear sky, or on a lightly cloudy day. You may prefer shade in hot climates in summer: the modest heat of the reaction added to the heat of direct summer sun could dry the paste or warp some plastic parts

You can set it up indoors with a UV lamp, but place the lamp at least 18" (50cm) from the tray, so the heat from the lamp doesn't add to the heat from the reaction.

Resist the temptation to deyellow intact electronics. I know some of you will do it anyway, once you've had some practice, but don't say I didn't warn you. (Trained mockers are standing by!) Instead, remove the chassis as much as possible, put sandwich bags over any remaining exposed metal, Remove any logos, stickers or decals (especially aluminum sheet decals or aluminum shielding paint inside some electronic devices, both of which can get quite eaten up and cause splotchiness) -- a heat gun or hair dryer will help you peel them off intact with a sharp razor blade. If you prefer, seal them in situwith wax, hot glue, or even tape (but tape isn't always reliable for this)

Just before use, dissolve the small amount of Oxy-clean in some water then mix that into your goo. Brush it liberally into the yellowed surfaces. You may choose to wrap the piece in clear plastic kitchen wrap to reduce evaporation: drying concentrates the ingredients and can cause splotchiness.

If you've done everything properly, the brushed-on paste should quickly foam a bit under the UV.

I'd try to check in on the progress every few hours, until you get a feel for the strength of you personal recipe. In my experience, a 6-12% peroxide mix should nearly or completely deyellow  a chassis in 3-8 hours with no damage if the piece is left from dawn to dusk.

A TRIAL OF TOTAL IMPROVISATION
After a few tries, it becomes very easy. In fact, the reason I wrote this up was because I did a totally slap-dash job this morning that came out fine. I needed to de-yellow the diffuser (cover) of a large fluorescent lamp for a project, but we've only had maybe half a dozen fully sunny days in he last two months. As I was headed out the door, I remembered this would be one of those days, but I didn't have time to mix a batch, find a big enough tray, etc., so this is what I did:

Reasoning that the translucent diffuser would be fairly transparent to UV, and was also not nearly as badly yellowed as an opaque object of similar ugliness, I sprinkled a pinch of oxyclean in a large sheet of plastic wrap, placed the diffuser on top, then sprinkled another pinch of oxyclean. I then folded the saran wrap around the diffuser, put it in a shallow cardboard tray to keep the ends from unfolding, and carried it to the sunniest part of my deck, where I carefully opened one end, and poured in some ordinary 3% peroxide (probably much weaker -- it was old).

In spite of taking so many liberties, each of which weakened the deyellowing effect, the job was mostly done when I got home. Had I not been using old 3%, I would have rinsed it off, to avoid undesired non-UV peroxide reactions that might slowly make the plastic brittle, but since the "3%" was probably more like1-2% to start with, and is probably much less now, I just left it out for tomorrow, to do what it can with the morning sun, if I stagger home in the wee hours tonight.

#2 Shoshana

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Posted 10 July 2009 - 10:51 PM

What's the best temp range to do this in? I might try this this winter when it's not so hot outside...

#3 Orpheus

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Posted 11 July 2009 - 12:13 AM

Pretty much anything between freezing and "hot", oh, wait, you're in Texas -- make that "normal".

It'd depend on the item and the plastic, of course, but 80F is pretty safe. Heck, I did it at over 80F today and didn't think twice, but your direct sun is stronger than mine.

How about below 90F (32C)? Injection molded plastic parts can warp enough to affect their fit (due to internal molding stresses) at as little as 125F-135F, even though an intact chassis may not be affected at that temperature (When assembled, it is uniformly loaded/reinforced by design). Take 90F air temperature plus heat from direct sun (the inside of a car can exceed 140+ on a 90F day), the cleaning reaction, the breakdown of hydrogen peroxide -- you get the idea

Most of the bromine in the plastic is still there, and will continue to mobilize. so yellowing may recur in time, especially if the plastic is exposed to heat and UV. I don't have a way to stop that BUT since the problem isn't really bromine or its mobility, but the fact that it reacts with atmospheric oxygen to stabilize at the surface as a brown stain, you might try rubbing  the cleaned, dried parts with Armor-all or similar to reduce contact with oxygen.

Furniture polish may work. I diligently hand-rubbed my weight machine with furniture polish when I got it in the early 90s, and it doesn't have any rust, but I've seen similar untreated machines rust in just a few years, even unused.

Ironically, bromine and bromide solutions tend to be fairly decent oxidizers and bleaches, themselves. But as I said this reaction isn't as much about bleaching or oxidizing or cleaning, it is about destabilizing the surface bromine.

#4 Shoshana

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Posted 11 July 2009 - 04:26 PM

'k thanks! It's too hot now - it's already over 90 by 9 am on it's way to 100+ in our current heatwave.

Thanksgiving to Christmas time might work. Temps are usually under 90 by then.

#5 Enkephalen

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Posted 12 July 2009 - 02:52 AM

Quote

It turns out to be relatively easy to remove these stains with common household materials. You may be surprised how "factory new" some items feel after deyellowing.

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#6 Captain Jack

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Posted 12 July 2009 - 07:30 PM

Interesting.  I have a question.

I have a vintage thing that is molded in white.  Made in the 80's, and has yellowing on the plastic.  How far through, I don't know.  Looks good on one side, yellowing on the other.  Some areas are painted and I do NOT want to remove the paint as I will never be able to match how it was done from the factory.  Will your formula damage the paint?

Also, can I just use oxy clean?  Or do I have to mix it with Hydrogen Peroxide?  If so, do I really need food thickener or can I get by without it?  Thanks.
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#7 Orpheus

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Posted 12 July 2009 - 09:02 PM

Though quite new, this process is already being widely used for game consoles/computers from the 70s/80s. Plastics from the 60s and earlier were substantially different. Telephones used "modern" ABS in the 1960s, but were considered exceptionally durable for household objects: the Bell System owned all phones until 1978, not the consumer, so Bell designed them to last for 30+ years -- and they did! (When China gave the US a pair of pandas in the 70s, they needed an "indestructable" ball. The public nodded in knowing approval when ABS was chosen: the toughness of Bell's ABS phones was legendary) None of my old ABS phones have yellowed, so they may not have used bromine additives yet.

The results with 70s/80s ABS have been quite good. There is only occasional surface damage, almost always from use of >12% (>40 volume) peroxide, overly long exposures (days) and/or preexisting UV damage from many years in a window or in a fluorescent-lit office. The damage I've seen pictures of has been very mild -- a superficial roughening from removal of a thin layer of damaged plastic or a light mottled "flush" which can be mostly evened out with Armorall.

Many of these consoles had painted logos, adhesive decals, pop-out plastic logos (e.g. the Apple logo on early Macs was a pop-out piece which could be pushed out from its apple shaped depression through a hole on the inside of the case) or aluminum logo plates. These should be removed, if possible (a hot air gun and a sharp razor work well) or thoroughly sealed to keep the peroxide out: there is a definite risk of damage to decals/paint and aluminum may react/dissolve.

Try Googling "peroxide" and your item. Someone may have already tried it.

You definitely need the peroxide and UV. While the perborates and perchlorates of the Oxy-Clean may help, we're really using it for its trace of of TAED catalyst, which acts on the hydrogen peroxide. Almost any other catalyst will break hydrogen peroxide down to water and oxygen or active oxygen radical (which is also how it spontaneously breaks down by itself), but TAED apparently catalyzes a different pathway in addition to the usual one, releasing trace H+ ions, which are normally added to chemical reactions via acid. As I said, the small amount of catalyst keeps it all under control.

You don't need a thickener. I first saw it in the blog of someone who used immersion trays. Thickener is just a convenient/economical way to keep the peroxide mix in contact with the plastic during hours of UV illumination.

If the entire chassis is painted vs just logos, it may not be a suitable material for this process.

#8 Captain Jack

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Posted 13 July 2009 - 02:41 AM

Ah, so it will remove the paint.  Bummber.  :(  Stupid '80's plastic... :cry:
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#9 D.Rabbit

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Posted 14 July 2009 - 10:09 PM

Since you mentioned "lawn furniture" in your first paragraph Orph, I thought, though it has probably nothing to do with the bromides, that the best way to brighten up grayed white lawn furniture, is to use methyl hydrate/gas line antifreeze.
Works for me.
Never tried it on other plastics, never had a reason to.
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#10 Orpheus

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Posted 15 July 2009 - 10:23 AM

Yes, "graying" and "browning/yellowing" are two different mechanisms. I think older plastic lawn furniture avoided bromine because constant outdoor UV could have made them yellow in a season or two.

For non-Canadians: methyl hydrate (= MeOH = CH4OH) is just another name for methanol. Its the preferred name for gas line anti-freeze on "Ice Road Truckers" (a History Channel series on the Canadian ice roads)

#11 Mark

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Posted 06 August 2012 - 04:27 PM

Mark: You know, it's amazing to me that nearly every time I glance at our online list, there is a guest in this thread. I realize de-yellowing plastic is a fascinating subject, but this thread is quite old now. I've never bumped a thread this old, but for the sake of those visitors I've seen who must be interested in this, perhaps we should re-address the topic. Any new ideas? Any new developments?

edited to add: There are three guest currently viewing this fascinating thread. I find that very intriguing.

Edited by Mark, 06 August 2012 - 04:28 PM.

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#12 Orpheus

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Posted 07 August 2012 - 01:07 AM

FWIW, my ongoing investigations show that ordinary "drugstore" hydrogen peroxide actually works quite well in strong summer sun or with repeated application. While I still use a thickener (to make a gel that stays in place), it's not necessary. Saran wrap may trap enough of a peroxide layer to get the job done if you use "fresh" peroxide, vs an old/opened bottle

So reduced to its basics, you only need drugstore peroxide and a touch of activator -- both of which you probably already have.

As with so many things, the more you do it, the less precise you find you need to be, until after a dozen or so tries, you can get by with a lick and a promise. Carl Jung called this "morphic resonance" and used it to explain why some scientific hallmarks (like the crystallization of new substances) may be all but impossible for years, but once achieved, soon turns out to be easily done by any undergrad in any obscure college closet. His theory may be a bit metaphysical for most people's tastes, but it's such a strong empirical experience (once you think to look) that perhaps a little metaphysics can be forgiven or even desired.

-- Orpheus "never underestimate the power of a lick and a promise"

#13 Mark

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Posted 07 August 2012 - 03:00 AM

Orpheus:

Quote

As with so many things, the more you do it, the less precise you find you need to be, until after a dozen or so tries, you can get by with a lick and a promise.

Mark: Like so many of my past relationships. :no:
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