Author Topic: Another Peroxide Experiment.  (Read 5181 times)

unbeldi

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Re: Another Peroxide Experiment.
« Reply #15 on: May 11, 2015, 04:49:59 PM »
I have been reading this string with interest; I have a tenite ivory WE302 to de-yellow.  I am a little confused.  I was assuming that you put the treated phone in the sun for the heat.  So, you are putting an OPAQUE peroxide paste on the phone and the UV rays from the sun speeds up the whitening?  Perhaps it is the science teacher in me but has anyone tested this claim?  Does the shady side get less whitening than the sunny side?  If I am patient, can I get the same results indoors?  If so, how long?  Just wondering.  Thank you for the clarifications.
Tina Loyd

Hi Tina,
It may indeed seem paradoxical as far as the transparency issue is concerned, but the more near-ultraviolet light is present the better these treatments do appear to work. I think high-energy light sets free more agents in the mixture for the reaction and perhaps helps overcoming the energy barrier of reaction (Arrhenius law).  The same can be achieved with strong UV-rich indoor lamps, and this is in fact usually the recommended setup.

For the ivory Tenite housings, I actually prefer using simple Clorox bleach which is much cheaper and available everywhere.  I cover up all ink stampings (date, H1 mounting code) with petroleum jelly to protect them and simply set the whole housing into a container with a mixture of ca. 30% to 50% Clorox and warm/hot water.  Then just let it sit outside in the sun for a half day or more. This works very well on the ivory plastic. Since the solution is clear, it is easy to check the progress.

[PS: also cover up the brass inserts for the base mounting screws, as brass is readily oxidized by the bleach. ]

Here is a phone that I bleached this way:
« Last Edit: May 11, 2015, 08:22:25 PM by unbeldi »

Offline Brinybay

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Re: Another Peroxide Experiment.
« Reply #16 on: May 11, 2015, 06:07:41 PM »
The retrobright treatments I did involved an ordinary incandescent bulb.
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Offline WEBellSystemChristian

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Re: Another Peroxide Experiment.
« Reply #17 on: May 11, 2015, 07:39:11 PM »
I have no idea why, but UV rays really speed up the peroxide process. Use peroxide by itself and it defades very, very slowly. Use UV by itself, and it uses the reverse effect on the plastic!

It has nothing to do with heat, just UV exposure.
Christian Petterson

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Offline TelePlay

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Re: Another Peroxide Experiment.
« Reply #18 on: May 11, 2015, 09:40:01 PM »
I have no idea why, but UV rays really speed up the peroxide process. Use peroxide by itself and it defades very, very slowly. Use UV by itself, and it uses the reverse effect on the plastic!

It has nothing to do with heat, just UV exposure.

Okay, I'll take a whack at a simple explanation of the process.

Quite right on the "just UV exposure" statement.

Normally, two Hydrogen Peroxide (H2O2 molecules break down slowly, or more rapidly with a catalyst, into one molecule of water (H2O) and one Oxygen (O2) molecule. When using a catalyst, such as potassium iodide, the break down into water is quite rapid and the gas bubbling off is pure oxygen, which is dangerous in quantity. This is the normal decomposition reaction:

     2 H2O2 --->  2 H2O + O2



UV light does something much different to Hydrogen Peroxide. It splits one hydrogen peroxide molecule (H2O2) onto 2 free hydroxyl radicals   (2 OH-)

     H2O2 ---> +UV Light --->  2 OH-

The hydroxyl radicals are very strong oxidizers which in the presence of ABS plastic interact with the pi bonding to reverse the damage done to those bonds over time, damage which causes the plastic to absorb more light, to appear darker. The complex pi high orbital bonds are responsible for both absorbing and reflecting light. The free radical hydroxyl ions must restore the original plastic molecules surface bonds to what they were originally and the result appears to be a "bleaching" of the plastic, lightening it in color by reflecting more of the full spectrum light making it look lighter.

So, without UV light, you don't get the strong oxidizing free radicals, and you don't get the desired affect.



Okay, you organic or physical chemists out there, start with this and correct any of it if I got anything, or everything, wrong (the new memory card has not yet arrived and it's been a long time since this was fresh in my mind).
            John . . .

              

Offline Brinybay

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Re: Another Peroxide Experiment.
« Reply #19 on: May 12, 2015, 12:27:58 AM »

Okay, I'll take a whack at a simple explanation of the process.
...
So, without UV light, you don't get the strong oxidizing free radicals, and you don't get the desired affect.


Maybe that's why it took 4 or 5 treatments to get mine white.
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Offline TelePlay

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Re: Another Peroxide Experiment.
« Reply #20 on: May 12, 2015, 07:59:29 AM »
Maybe that's why it took 4 or 5 treatments to get mine white.

Should have attached this table to the prior post. It shows the relative strength of several oxidizing agents. The hydroxy radical (OH-) is the strongest of those listed with atomic oxygen (O2) being right below it followed by ozone (O3), hydrogen peroxide and chlorine (the weakest).

So, without the UV light, hydrogen peroxide will have an affect but a lot slower.

Some people add Oxyclean to their peroxide mixture of choice. Oxyclean is 50-60% Sodium Percarbonate

Sodium percarbonate has 3 peroxide molecules in its formulation and in crystalline (dry) form is stable. When water is added to it, it breaks down to release the 3 hydrogen peroxide molecules and leave 2 sodium carbonate (soda ash) molecules in the solution.

     2 Na2CO3.3 H2O2 ---> 2 Na2CO3 + 3 H2O2

So, adding Oxyclean to a hydrogen peroxide solution (which contains water) releases even more hydrogen peroxide, increases the concentration of hydrogen peroxide, which in the presence of UV light will oxidize the plastic, do the job faster than just the hydrogen peroxide solution alone.

Interesting, isn't it.
            John . . .

              

unbeldi

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Re: Another Peroxide Experiment.
« Reply #21 on: May 12, 2015, 09:03:59 AM »
onto 2 free hydroxyl radicals   (2 OH-)

     H2O2 ---> +UV Light --->  2 OH-

The hydroxyl is neutral, not an ION!  You cannot create two negative entities from a neutral one, no matter how much UV is used. Photons cannot be converted to electrons yet.

Quote
The hydroxyl radicals are very strong oxidizers which in the presence of ABS plastic interact with the pi bonding to reverse the damage done to those bonds over time, damage which causes the plastic to absorb more light, to appear darker. The complex pi high orbital bonds are responsible for both absorbing and reflecting light. The free radical hydroxyl ions must restore the original plastic molecules surface bonds to what they were originally and the result appears to be a "bleaching" of the plastic, lightening it in color by reflecting more of the full spectrum light making it look lighter.

So, without UV light, you don't get the strong oxidizing free radicals, and you don't get the desired affect.


The lifetime of a free hydroxyl radical is only on the order of picoseconds, perhaps nanoseconds. Lisa's paradox questioned how this agent could possibly be effective on the plastic surface when removed from it in the thick paste where it was likely created, because the light might not penetrate that far.

While true that aging of plastic has damaged the surface by oxidation, your story does not explain how even more oxidation by hydroxyl radicals, or any oxidizer, would all of a sudden repair the damage. Usually oxidation doesn't repair anything, but causes harm.

The discoloration of plastics is due to the fillers used in them to tune their properties. Especially responsible are the flame retardants added to prevent the plastic from burning and providing more fuel for existing fires. Many of these contain bromides which deteriorate and release elemental bromine. Bromine is very intensely colored, so even extremely small amounts discolor plastics yellowish and brownish.  The bleaching processes oxidize the bromine, or other discoloration, and make it colorless once again, thus restoring the original color of the plastic.  But basically, the oxidation is always a process of destruction of pigments, and one has to be very careful to not be so aggressive that the desired pigments of the colored plastic are destroyed too, causing fading. This can easily happen with the pastel colors, such as pink and aqua blue. This can only be reversed by sanding the damaged areas, as the penetration is not deep.

The destructive power of the bleaching process also appears in the fact that the plastics after bleaching appear rather dull, the gloss is greatly reduced and must be restored by polishing.