Characterization of Polymer Aging: A Review

Polymer aging under environmental conditions causes deterioration of service properties. Understanding the aging behavior and mechanism is important not only for lifetime prediction, but also for material improvement and development. Therefore, comprehensive characterization of polymer materials during aging is crucial. In this review, various analytical methods for characterization of chemical changes, physical changes and service properties are introduced. Based on that, methods for stabilization evaluation and lifetime prediction, especially sensitive evaluation methods are reviewed. Chemical changes include molecular weight changes by chain scission and crosslinking, functional group changes on the surface and in the bulk, formation of free radicals, formation of small molecular species as the degradation products, and chemical distribution by heterogeneous aging and additives migration. Physical changes include crystallization changes (post- or chemi-crystallization) and morphology changes (cracking, debonding, etc.). Service property changes include deterioration of processability, mechanical properties, electrical properties and appearance. In the end, existing problems and future research perspective are proposed, including relationship between chemical/physical changes and service properties, introduction of modern mathematical and computer tools.