Materials Science and Engineering: My silicone cell phone case is yellowing. How do I make it clear/white again?

Buy a new one and put over the existing one. Voilà!

Polymers (including silicone rubbers) commonly turn yellow due to the process of ageing. The process, which is irreversible, is exacerbated when the polymers are exposed to heat, light or certain chemicals. Usually, the discolouration does not in any way affect the function of the object. While all polymers discolour over time, the problem is particularly prevalent with cheap, poor quality products. If you bought your silicone phone case on eBay or Amazon for only a few pounds/dollars, then the product quality is likely to be poor. You tend to get what you pay for. Hope this helps.

Yellowing of polymer materials is mainly due to degradation reactions (thermal, photooxidation, radiation, oxidation). These reactions are chemical in nature, so irreversible. You cannot make them "white" through using any kind of chemical substance, such as chlorine bleach and peroxides. Actually, these chemicals may worsen that discoloration, as they are oxidizing agents. If that "yellowing" is just an esthetical problem and there is no application functional failures, just use the product until it dies. But, if the discoloration is important, then it must be replaced by a new one. The original appearance cannot be recovered as degradation reactions are permanent and irreversible.

Silicone might get discolouration when in contact with certain substances and surfaces. UV rays are known to cause some damage to silicone cases, but there's also neoprene/latex,sunscreen preparations, chlorine and others, which can damage the structure and colour of your silicone case. Some suggest that putting the silicone case in the fridge for a couple of hours might bring back its colour, yet this unproven method is not directly correlated with the chemical properties of this material, therefore speculators say it won't do any change.

Yellowing of Silicon is due to a photochemical reaction that happens when kept exposed to light for prolonged duration.There is no way to revert it, however there are agents called anti-yellowing agents that need to be added at the manufacturing state.Sorry you are not so lucky after its yellowed. if it isnt already try to keep in a dark place.

In most of the cases, the cause of this yellowing is due to molecular reaction and breakdown which happens when these material are exposed to the ultraviolet rays from the Sun. Unfortunately, most of these are irreversible.

You can give a try following the instruction on this link http://www.technewsworld.com/story/79152.html This should work :)

Unfortunately the answer is most likely there is no way to reverse the color change. The reason is that the plastic itself has changed color. Probably does to some degree, but more than likely you won't be able to get it looking like new. That's the problem with TPU/silicone cases. They just all turn yellow after a while.

I've been using a black rubbery silione case for my phone for years -  it cost £1.00 ($1.50) and it's still as good as new. The sucker thing that holds my satnav to the ar window is suffereing the same malaise as your phone case.  Thats a problem - I was hoping that some of the other answers would suggest some way to re-soften it (I'm not worried about the colour) but no such luck so far ... so I've posted a separate question