Rubber elasticity

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Rubber elasticity refers to the ability of solid rubber to be stretched up to a factor of 10 from its original length, and return to close to its original length upon release. This process can be repeated many times with no apparent degradation to the rubber.^[1]

Rubber, like all materials, consists of molecules. Rubber's elasticity is produced by molecular processes that occur due to its molecular structure. Rubber's molecules are polymers, or large, chain-like molecules. Polymers are produced by a process called polymerization.^[2] This process builds polymers up by sequentially adding short molecular backbone units to the chain through chemical reactions. A rubber polymer follows a random winding path in three dimensions, intermingling with many other rubber polymers.

Natural rubbers, such as polybutadiene and polyisoprene, are extracted from plants as a fluid colloid and then solidified in a process called Vulcanization. During the process, a small amount of a cross-linking molecule, usually sulfur, is added. When heat is applied, sections of rubber's polymer chains chemically bond to the cross-linking molecule. These bonds cause rubber polymers to become cross-linked, or joined to each other by the bonds made with the cross-linking molecules. Because each rubber polymer is very long, each one participates in many crosslinks with many other rubber molecules, forming a continuous network. The resulting molecular structure demonstrates elasticity, making rubber a member of the class of elastic polymers called elastomers.^[3][4]