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Kom over dette på Eurobricks. Jeg kan lite eller ingenting om kjemi, men denne karen ser ut til å vite hva han snakker om. Det er et par interessante poenger her med tanke på hva som har vært nevnt i denne tråden om bl.a. gjenbruk av blekemiddel og å ha lokk på beholderen man bruker...
"Lego parts are made from a type of plastic called ABS which stands for Acrylonitrile Buadiene Styrene. It's a mixture of three different chemical compounds that forms a tightly knit, sturdy, and workable end product. The product, however, is not free from catching on fire and creating problems. Therefore, manufacturers also include a flame retardant in the mixture to stop it from spreading fires. The flame retardant used is generally a brominated compound meaning that it has bromine atoms in there which are readily "dislodged" from the molecule which is what helps it stop fires from spreading.
The problem with bromine is twofold. One problem is that the bromine atom when it attaches to something is generally not very tightly attached. Therefore, when something like a photon of UV light hits the chemical bond, it will break the bond and free the bromine atom. This bromine atom will then attach to something else and not what it was originally attached to. The second problem is that elemental bromine is a nasty, deep brown, volatile liquid. Volatile meaning that it readily vaporizes. The name of the chemical element, bromine, comes from the Greek "Bromos" meaning "stench" as the element smells like a skunk that has taken a bath in bleach. (Not that surprising since, like chlorine, bromine is a halogen).
Anyway, when you have your white or light gray Lego pieces out in the sunlight, the UV rays will interact with the brominated flame retardant in the ABS plastic and "knock" a bromine atom free. If this bromine atom binds to another free bromine atom in the mix it will form elemental bromine. That dark brown, nasty substance I just described. As this bromine is trapped within the tightly bound structure of the ABS plastic, it will sit there and you'll see the discoloration showing up.
What the retr0bright method does is generate a good deal of oxygen gas from the decomposition of the hydrogen peroxide. Under UV light (whether from a UV lamp of the sun), the UV light will break apart that bromine bond and cause the bromine to bind with the free oxygen generated from the peroxide decomposition. At the same time, the heat of the reaction expands the plastic at a molecular level allowing the oxygen atoms to get in there, or unbound bromine atoms to get out. It doesn't need to get deep into the ABS pieces since the breakdown of the flame retardant generally happens on the surface. (As is seen by the fact that parts of pieces not exposed to UV light are generally still close to the original color).
Unlike what many in this thread have stated, this process is NOT "dissolving" away the top layer of plastic on the Lego piece. Any softness that may be noticed is likely due to the heat generated by the chemical process which will of course soften the Lego pieces. In addition, if you leave it in the peroxide solution for too long, the peroxide (especially if it's concentrated) can attack the ABS itself and cause problems. However, if you watch the pieces and take them out as soon as the discoloration is gone, then go and wash and dry the pieces, all will be fine.
Some things to keep in mind:
Do NOT put this solution in a sealed jar while the reaction is happening! This is especially true for the more concentrated peroxide solutions as there will be a LOT of oxygen gas generated. If it's in a sealed container made of glass, you might have a bomb ready to go off. ALWAYS leave the cap on loosely so gas can escape.
You also cannot re-use the solution. As time goes on, the peroxide decomposes and becomes more dilute and therefore less effective. So after one or two uses, you have to throw it out.
ALWAYS wear eye protection and gloves. ESPECIALLY with the more concentrated solutions. You do NOT want this stuff in your eyes as it WILL blind you. You also don't want this on your hands/fingers as it will cause nasty little burns that will take time to heal.
Keep in mind the temperature. You don't want this getting too hot as it will start to damage the pieces and the decomposition of the peroxide increases as the temperature goes up, releasing more heat, etc. etc. Try to keep it as room temperature as you can.
UV light is really key to the process. Any changes you see without UV light are likely caused by the peroxide eating away at the surface of the plastic.
Make sure that the peroxide you use only contains hydrogen peroxide and water. You don't want to use brands that have other chemicals in there (especially true of hair product peroxides) as these are likely to attack the ABS in unexpected ways.
Just my thoughts as a chemist and a Lego fanatic myself who wants to ensure the safety of everybody, the restoration of aged parts, and fun!"
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