The Joule Effect

Glove Consumer: I wonder if others have experienced what I have with the donning of latex medical gloves. If I stretch the glove to some extent in the process of donning it, I feel an obvious warming of my skin by the glove. But when I release the stretch to allow it to retract immediately, I could feel a cooling sensation.

Have you experienced this yourself? Can you explain this unexpected observation of mine?

JohnWoon: Yes, I've experienced this indeed but I expected it. This is what rubber technologists refer to as the "Joule Effect".

When natural rubber is stretched, before or after vulcanization, it produces heat and becomes warm as opposed to some metals which tend to cool when stretched. Also, a stretched rubber is expected to retract on heating i.e. when it absorbs heat.

The effect is more pronounced if you stretch the glove more quickly.

Some early reports speculated that as rubber was stretched, the orientation and orderly alignment of the rubber molecules coupled with the inherent van der Waals forces resulted in the immobility of the rubber molecules. Hence the mobility could only be reversed as the temperature increases. The deduction was that if rubber is elongated quickly it releases heat and as the stretching is quickly terminated, it absorbs heat, hence your reporting of the "cooling" sensation.

Having said this, I'd like to draw your attention to the fact that at low elongation, you might actually get a cooling effect. Also, the heat evolved as you've observed has nothing to do with the evolution of heat through repeated cycle of flexing (deformation) of rubber. In the latter case, the heat is a result of "hysteresis". Let me know if you don't understand the meaning of this term.