Rubber stiffness as a function of temperature?

In summary, rubber behaves as an entropic spring where increasing temperature increases its stiffness. However, at higher temperatures, rubber transitions from a glass-like state to a leathery state and then a rubbery state, causing a decrease in modulus. This is due to an increase in free volume. Additionally, high Tg summer tire compounds can become dangerously stiff in winter temperatures. These seemingly contradictory behaviors may be explained by the different definitions and measurements of modulus in each circumstance, as well as phase changes that occur in rubber at different temperatures.
  • #1
JJD
1
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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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  • #2
Phase changes; "rubber" is a general word. Every time you cross a phase boundary you get a whole new set of properties.
 

1. What is rubber stiffness?

Rubber stiffness refers to the resistance of a rubber material to deformation or bending. It is a measure of how easily a rubber material can be stretched or compressed under an applied force.

2. How does temperature affect rubber stiffness?

Temperature has a significant impact on rubber stiffness. As the temperature increases, the stiffness of rubber decreases, making it more flexible and easier to deform. On the other hand, as the temperature decreases, the stiffness of rubber increases, making it harder and less flexible.

3. What is the relationship between rubber stiffness and temperature?

The relationship between rubber stiffness and temperature is an inverse one. As the temperature increases, the stiffness of rubber decreases, and vice versa. This is because temperature affects the molecular structure and interactions within the rubber material, leading to changes in stiffness.

4. How is rubber stiffness measured?

Rubber stiffness is typically measured using a tensile testing machine, where a sample of the rubber material is pulled or stretched at different temperatures. The force required to deform the rubber is measured, and the stiffness is calculated as the ratio of stress to strain.

5. What factors can affect the temperature-dependent stiffness of rubber?

There are several factors that can affect the temperature-dependent stiffness of rubber, including the type of rubber material, its molecular structure, the amount of cross-linking within the material, and the temperature range being tested. Other external factors such as humidity, pressure, and strain rate can also impact rubber stiffness at different temperatures.

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