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Rubber-bands are simple, yet very useful. Old rubber bands(5 years?) get brittle? Why is that?

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Here is an interesting fact: In "Surely You are Joking Mr.Feynman", Feynman talks about how he used to fix old typewriters using rubber bands when he was a kid. When he moved into California, the trick did not work as the humidity levels were different (he was in NY when he was a kid). –  Bernhard Heijstek Jul 16 '11 at 6:19
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I do not know what kind of rubber bands Feynman used, but I know that humidity is not the factor which made his repair short-lived in California. Rubber life depends on light, temperature, color, ozone and in extreme cases on some kinds of photochemical smog. –  Georg Jul 16 '11 at 10:33
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How inclusive of this group to allow and answer a chemistry and engineering failure question! ;-) –  bmike Jul 16 '11 at 23:08
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1 Answer

up vote 2 down vote accepted

If a rubber band is usable for 5 years, it's a very good one.

There is not much You can do, just store them in a dark and cool place. Light plus oxygen is the most dangerous enemy of rubber. Nothing can be done in use.

The biggest influence has the producer, because he can choose a persistent (expensive) kind of rubber (eg Kalrez®, ask for prizes!) Of course there are less extreme rubbers in prize. Another way is the color, adding carbon black prolonges life of rubber substantially. (Protection from light) and to add some antioxidants.

The background of embrittlement of polybutadiene (polyisoprene) based rubbers is crosslinking by radical chain reactions with oxygen. Cheap urethane rubbers die from similar reactions, but those usually become sticky, even liquid by this processes.

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OK, can I have some "prizes" please?! I think you meant 'prices' @Georg, +1 for a good answer all the same ;-) –  qftme Jul 16 '11 at 16:43
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Right! I'll let that as it is, to avoid that Your comment is strange. –  Georg Jul 16 '11 at 16:45
    
Very informative and thorough answer! Thank You So Much! –  Adel Jul 16 '11 at 18:34
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