The Language of Rubber – Part 4 (Resilience, Heat Built-Up and Hysteresis) By John Woon (Senior Latex Consultant)

Resilience is usually expressed in percentage and it measures the ratio of energy given up on releasing or recovery from the strain (i.e. deformation) to the energy required to produce the deformation.

When a natural rubber ball is dropped on the floor from a certain height, the impact or stress the ball gets when it hits the hard surface would force the rubber molecules to strain, stretch, reorganize or deform. This results in potential energy being stored in the molecules when the ball is in a state of strain. At the end of the impact i.e. when the stress is released, the rubber molecules would retract like a spring to its original unstrained state. The stored potential energy is hence recovered in the form of "bouncing" of the ball.

Natural rubber, being a very elastic elastomer, has good rebound resilience of more than 80%. On the other hand, in semi-elastic rubbers such as Butyl, the bouncing recovery is poor at normal ambient temperatures as most of the energy is turned into heat on impact. (For this reason Butyl rubber is sometimes used for damping applications)

Hysteresis is the percentage energy lost after the cycle of deformation i.e. 100% minus the resilience percentage. Hysteresis is due to internal friction of the rubber molecules resulting in the formation of heat energy. The higher the elasticity, the higher would be the resilience and hence the lower would be the hysteresis.

It would be interesting to compare an elastic latex glove with a lesser elastic glove like a Nitrile glove by repeatedly stretching and releasing and feeling the difference in the resultant increase in the warmth of the gloves.

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