Whitening plastics – retrobright – how I do it

In the past I carried out several experimental whitening treatments on plastics from old computers, with varying results. I watched a number of videos and read various articles dealing with this activity – restoring the original colour of old plastics. To be honest, I skipped recipes involving baking soda, vinegar, chlorine, bleach and similar substances and decided on peroxide. My father, as a hunter, always bleached trophies with peroxide, so I had seen with my own eyes that it is effective and works. I would certainly like to try methods other than fairly aggressive peroxide. Perhaps there will be more time someday.

Why plastics turn yellow

The reason plastics turn yellow is so-called photo-oxidation. In short, exposure of plastics to UV radiation (part of sunlight) leads to degradation of some bonds in the polymer. UV radiation causes Cl (chlorine) to break away from side chains. In combination with oxygen, a reaction occurs and new structures are formed that absorb some of the shorter wavelengths of light, causing yellowing. Over time the yellowing worsens as the polymer degrades overall. Another consequence of long-term exposure of plastics to UV radiation is embrittlement, which can eventually lead to cracking or complete disintegration. I didn’t come up with this myself; I found it on Google. I can only assume that this description reflects the real cause of plastics yellowing.

Different plastics from different manufacturers behave differently. Some may yellow more, others less. This is due to the different plastic “recipes” used by manufacturers, who may enrich plastics during production with various protective additives – stabilisers that resist UV radiation better.

How I whiten yellowed plastics

After unsuccessful attempts involving hairdressing peroxide gel and wrapping plastics in stretch film, I tried, on a friend’s recommendation, immersing the plastics in a mixture of 30% peroxide and warm water. This method worked well for me, so I describe my exact procedure for anyone who needs to restore the original colour of plastic products.

Plastic whitening procedure – step by step

For trouble-free whitening of plastics you need:

• a sufficiently large transparent container
• 1 to 2 litres of 30% peroxide
• warm water
• galvanised nuts
• rubber gloves
• glasses
• clothing (long sleeves, long trousers)

1) In warm water with a little dishwashing liquid, I use a soft brush to remove all dirt and stickers from the plastic. It is important to be thorough and clean various marks as well. After washing, I rinse everything thoroughly.

2) For this purpose I had a glass aquarium custom-made, but it is easier and cheaper to buy an ordinary transparent plastic box with a lid of suitable dimensions from IKEA, Jysk or Albert. I had the aquarium made because glass is absolutely clear and should block UV radiation only minimally, which paradoxically is also needed to restore the original colour.

3) I place the rinsed plastic in the container and pour in clean warm water until the plastic is completely submerged. I then add 1 litre of 30% peroxide. I don’t worry about an exact ratio at all. Sometimes the plastic is larger and there is therefore more water, so I add a little more peroxide. The higher the proportion of peroxide, the faster the whitening proceeds – but only to a certain extent. Temperature and the level of sunlight also affect whitening. It is necessary to choose a completely sunny and warm day. Whitening then proceeds faster even with a lower peroxide content. Subjectively I feel that I use a rather “weak” mixture and could make it stronger, because even under favourable conditions whitening takes 5–10 hours or more, and the result is genuinely better only after longer application.

4) During whitening I check the condition, turn the plastics to different angles and make sure they remain fully submerged. I perform this check approximately every 30 minutes. Under ideal conditions the water in the container seems to fizz and constantly tends to lift the plastics to the surface. I found it useful to attach large galvanised nuts to the plastics before placing them in the bath; these pull the plastic down. I do not recommend weighting the plastic from its visible outer side. Once I weighted a piece of plastic with a glass ashtray; UV light did not penetrate through the thick glass wall and an unwhitened circle remained on the plastic.

5) Once I am satisfied with the degree of whitening, I remove the plastics and rinse them several times with water. It is necessary to be very thorough, because residues of solution running down supposedly rinsed plastic can, even at a low concentration, leave a mark in the form of a drying droplet. In nice weather the rinsed plastic fortunately dries within a few minutes, so this is no longer a risk.

Tips and my subjective opinions

After whitening, I treat plastics with a spray product intended for maintaining plastics in car interiors. It is more of a gentle, non-aggressive cleaner; it is not one of those greasy products that intensify the colour of plastics (I absolutely hate those even in a car). I have the feeling that the product somehow closes the open pores in the plastic and gives it a slightly more uniform appearance. Sometimes I feel that whitened plastics look somewhat dried out. But don’t worry!!! Nothing dramatic. I deliberately say these are my subjective impressions and feelings. If I handed the item to someone unfamiliar with the process, it would look completely OK to them.

When whitening, it is useful to keep a bucket of clean water next to you. Before removing my gloves I always rinse briefly, so I don’t have to worry about burning my fingers while taking them off. For the same reason I wear glasses throughout the entire process, because occasional splashes are unavoidable. And you know how it is… you can try a thousand times to splash clean water into your eye and fail, then the one time you are whitening with peroxide it splashes straight into both eyes. I use disposable rubber gloves, which last for the whole process, and I keep them for further use. I have also used thicker hardened rubber gloves. Their advantage is that they are quick and easy to put on and take off. The disadvantage is that they do not fit tightly around the arm, which could have unpleasant consequences if the peroxide mixture ran inside.

Summer and sunny days are ending, so I will now work on improving the whitening process in my photo box with UV lighting so that I can whiten plastics all year round.

The procedure described does not guarantee a completely perfect result. Each person bears responsibility for any injury or irreversible damage to plastics. The consequences of soaking in a peroxide bath and its effect on the future lifespan of plastics have not, to my knowledge, been scientifically studied and published.