Why are my rubber bands losing their spring?

12 January 2016

Part of the show Why do we have pubic hair?

Rubber_bands.jpg

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Question

It's very hot and humid where I live, and I find that bags of rubber bands degrade faster than I can use them. I am going to store them in the refrigerator to see if that helps. Will that slow down the degradation? Do you have any other suggestions? Why do they keep losing their spring??

Answer

Kat Arney put this question to chemist Ben Pilgrim...

Ben - Actually, the thing that usually causes rubber to go off rather than being slightly too warm is exposure to a chemical that degrades the rubber. So there's some types of polymer, things like ozone in the atmosphere can react with but, even without that actually light is one of the big problems. Light can split oxygen into these radical species, these peroxides and, over time, these degrade the structure of the rubber. So, rather than keeping it cold, keeping it in the dark would certainly help. Now, it is interesting about the cold because, actually, if you cool rubber down too much, you actually cause it to decompose much faster and this is due to the rubber falling below something which we call 'the glass transformation' or 'glass transition' temperature, when it sort of has these rubbery like properties. If you go below that temperature, it becomes brittle. Now one of the most famous consequences of this was actually the cause of the Challenger shuttle disaster back in 1986. So the 'O' rings, which were made of rubber in the kind of engines and boosters for the rocket were very cold on the launch pad that day, because they'd had very freezing, very low temperature conditions and, therefore, they weren't flexible enough to seal properly and this then led to sort of hot gases coming out and eventually the very sad disaster. And this was demonstrated quite famously by Richard Feynman in sort of the inquest when he took one of these bits or rubber and put it in a glass of iced water in front of the panel and showed how brittle it became. So, I'd be careful about sticking it in the freezer - that might not be the best thing to do.

Chris - But when it warms up again, wouldn't it go back to normal behaviour?

Ben - Yes. But I say one of the main things is keeping it out of light and if you could keep it in a sort of airtight container so it doesn't have, for example, oxygen getting to it, that might help as well.

Kat - So. Keep them in a sealed, dark box.

Ben - Yes.