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Rubber stiffness as a function of temperature?

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  1. Feb 11, 2016 #1

    JJD

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    I'm aware of the concept of rubber as an entropic spring and how increasing the temperature increases the modulus/stiffness of the rubber. I've seen the experiment of how heating a strip of rubber supporting a load will cause it to shorten.



    But also a rubber will transition from its glass-like state to its leathery state then rubbery state as temperature increases. These graphs will show the modulus decreasing with temperature. I believe the explanation for this is the increase in free volume. Also, summer tire compounds (high Tg) will become so stiff in winter temperatures that they can be dangerous to drive on.
    http://www.azom.com/images/Article_Images/ImageForArticle_12100(9).jpg
    https://en.wikipedia.org/wiki/Time–temperature_superposition

    These two things seem contradictory. I'm guessing it has something to do with how modulus is defined or measured in each circumstance. What am I missing?
     
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  3. Feb 11, 2016 #2

    Bystander

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    Phase changes; "rubber" is a general word. Every time you cross a phase boundary you get a whole new set of properties.
     
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