Rubber elasticity

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Rubber elasticity" – news · newspapers · books · scholar · JSTOR (July 2024) (Learn how and when to remove this message)

This article's tone or style may not reflect the encyclopedic tone used on Wikipedia. See Wikipedia's guide to writing better articles for suggestions. (July 2024) (Learn how and when to remove this message)

Rubber elasticity refers to a property of crosslinked rubber, namely that it can be stretched up to a factor of 10 from its original length. When released, it returns very nearly to its original length. This can be repeated many times with no apparent degradation to the rubber.^[1]

Rubber is a member of a larger class of materials called elastomers and their economic and technological importance is significant. Elastomers have played a key role in the development of new technologies in the 20th century and make a substantial contribution to the global economy.^[2]

Rubber elasticity is produced by many complex molecular processes and its complicated explanation requires a knowledge base consisting of advanced mathematics, chemistry, statistical physics, and the concept of entropy. Entropy may be thought of as a measure of the thermal energy that is stored in a molecule.

Common rubbers, such as polybutadiene and polyisoprene (also called natural rubber), are produced by a process called polymerisation.^[3] The process starts off with very long molecules (polymers) that are built up sequentially by adding short molecular backbone units through chemical reactions. A rubber polymer follows a random, zigzag path in three dimensions, intermingling with many other rubber molecules. An elastomer is created by the addition of a few percent of a cross linking molecule such as sulphur.^[4][5]

When heated, the crosslinking molecule causes a reaction that chemically joins (bonds) two of the rubber molecules together at some point (a crosslink). Because the rubber molecules are so long, each one participates in many crosslinks with many other rubber molecules forming a continuous molecular network.

As a rubber band is stretched, some of the network chains are forced to become straight and this causes a decrease in their entropy. It is this decrease in entropy that gives rise to the elastic force in the network chains.