What causes rubber band oxidation?

Rubber aging refers to the process by which rubber products undergo chemical structural breakdown and performance degradation due to environmental factors. This degradation manifests primarily as physical changes such as cracking, stickiness, and hardening, as well as a decrease in mechanical properties.

Physical manifestations: Cracking (oxygen/ozone synergistic effects), stickiness (precipitation of chain scission products), hardening (increased crosslink density), and powdering (filler debonding).

Performance degradation: Tensile strength decreases by 30%-80%, and elongation at break decreases to 20%-50% of its original value.

Natural rubber is composed of polyisoprene chains. When stretched, these chains slip between each other. If raw rubber is too soft, other chemicals, such as sulfur, are added to create interlocking bonds between the chains, making the rubber harder and less prone to lathering. This process is also called vulcanization. Over time, ultraviolet light and oxygen in the air react with the rubber, generating highly reactive free radicals that cleave the polyisoprene chains into shorter fragments, returning the rubber to its original state. At the same time, these groups can also form new, short crosslinks between chains. This hardens the rubber and ultimately makes it brittle. Whether these reactions occur in a rubber band depends on the relative speeds of these processes, which in turn depends on the quality of the rubber, such as additives, fillers, and dyes.