Processes that occur in a polymeric material during a specified period of time, and that usually result in changes in physical and/or chemical structure and the values of the properties of the material.
Source:
PAC, 1996, 68, 2313. 'Definitions of terms relating to degradation, aging, and related chemical transformations of polymers (IUPAC Recommendations 1996)' on page 2315 (https://doi.org/10.1351/pac199668122313)