[Madidus_Scientia (OP)]

The ends of my sunglasses (the bits that go over your ears) are coated in black rubber, which over time has become sticky. Why does this happen? And is there any way the rubber can be restored to normal?

[Don_1]

I think the oils from your skin may be having an effect on the rubber.

Take a look at this article on Microbial Degradation http://aem.asm.org/cgi/content/full/71/6/2803 [Links inactive - To make links active and clickable, login or click here to register]. Its a bit involved, so you might want to just pop out and buy some new sunglasses instead.

[RD]

After thorough cleaning and drying, you could try rubbing talcum (baby) powder on the gooey rubber ... http://www.luzenac.com/rubber.htm [Links inactive - To make links active and clickable, login or click here to register]

... just pop out and buy some new sunglasses instead.

It maybe possible to fit new 'legs' to old (sun) glasses, (may make economic sense if they are prescription). 

[Madidus_Scientia (OP)]

Ah, I see. Wouldn't the manufacturers think to use a different type of rubber or just plastic? They're Oakleys so they're not really a cheap brand.

Thanks Don & RD

[techmind]

The rubber feet stuck on the bottom of bits of lab equipment can have a nasty tendency to turn to sticky goo over 10 years or so. Suspect it's something to do with the plasticiser ... but I'm no chemist.

[Bored chemist]

Ah, I see. Wouldn't the manufacturers think to use a different type of rubber or just plastic? They're Oakleys so they're not really a cheap brand.

Thanks Don & RD

They may blame your choice of hair care products; and then sell you some new bits.

[lintonatlas]

It appears there are many formulations of polymers so the reasons can vary depending on what the exact formulation was.

"There is therefore a large range of both sequential (or chain) reactions and competing reactions and that the ones which predominate depend on factors such as the composition of the vulcanizate as well as the influences of heat, light and metal catalysis. In heat ageing we are balancing the rate of reaction of oxygen with the elastomer and the rate of diffusion of the oxygen into the bulk material. If the temperature is relatively low, it has been postulated that for an unprotected vulcanizate diffusion predominates and therefore there is slow oxidation throughout the product, but as the temperature rises, the rate of oxidation increases much more than the rate of diffusion so substantial oxidation occurs on the surface and an oxidized (hard) surface skin is formed. As oxidation continues the chain breakdown may become more significant and the hard surface then softens and turns sticky. To complicate matters further, under certain conditions this order can be reversed and an initially sticky degraded surface can harden with further oxidation."

newbielink:http://www.bouncing-balls.com/chemistry_tech_conservation/ageing.htm [nonactive]