How do retro supply stores prevent the controller rubber replacement parts from "expiring"?

Question

My NES controller felt really awful. After ordering replacement rubber parts from a store, unscrewing my controller and replacing the original rubber parts with the new ones, it felt "like new" again.

Apparently, according to the person running the store, the rubber becomes hardened after X years, and that's why it starts feeling so bad eventually.

Even assuming that the NES controller I had was made in the mid-1980s, that's just about 35 years. And who knows how long it had already been "stiff" like that before I got it?

More than likely, the retro stores buy a large batch of these rubber parts at once, then resell them in small quantities to customers over years and years.

But then, if they spend years and years in stock, won't those rubber parts become "hardened" just like when they are inside the controllers? Just thinking about this stresses me out. And it's not just for the NES; SNES and Nintendo 64 and Saturn etc. also have such replacement rubber parts to buy, and those consoles were made much later than the NES. Quite "recently", really.

So how long does it really take for the rubber to "stiffen" like this? I had never heard of this being a thing before I experienced it myself. And does it only have to do with time, or does actual usage of the controller also matter?

The parts I bought came in a normal little plastic bag, which didn't seem especially air-tight or anything, so I assume that it starts aging as soon as it's manufactured.

Answer 1

So how long does it really take for the rubber to "stiffen" like this?

It can be within weeks or many years if not decades.

It all depends on the plastic mixture (it rarely is real rubber) and how it's stored. Usually longer if tight sealed.

I had never heard of this being a thing before I experienced it myself.

Most plastics are rigid by nature. They are fitted with Plasticizers to increase their plasticity, their ability to become soft and flex. You may have heard of Phthalates like DEHP or DOP as stuff that evaporates from plastic containers into food, sometimes acting like hormones? Well, they are in there so that container does not break right away and maybe can be squeezed to get out the last drop of ketchup. Similiar they are in artificial rubber to make it bendable.

And does it only have to do with time, or does actual usage of the controller also matter?

Time and storage. Phthalates and other plasticizers behave a bit like alcohol and evaporate over time. That's why a soft drink bottles put out in the sun for a year or so splinter into tiny pieces when grabbed. Evaporation is 'controlled' by temperature and pressure in relation to its vapor pressure.

Different plasticizers have different vapor pressure values. Thus evaporating over longer or shorter time in the same environment. But in general as higher temperature is, as more will evaporate. Similar as lower counter pressure is, as faster it will evaporate, stiffening the plastic.

In addition there is ofc also the base flexibility of the base plastic used and how it acts with the plasticizer.

Long story short, a 'good' plasticizer may keep a piece in the open flexible for many decades. Similarly, a piece stored in tight packaging at cool temperature (not freezing) and without light may as well evaporate only a little until opened.

Bottom line: Yes, it happens and it depends.

For everything beyond that, you may ask your friendly neighbourhood chemical engineer.

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One point missing here is that such 'rubber' pads don't have to be as old. Considering that NES type controllers are still built, chances are that this new piece isn't as nearly old as the one it replaces, but brand new.