Physical aging of polymer materials

Aging is any slow, irreversible change in the structure and/or composition of a material due to its own instability, interaction with the environment, mechanical stress, or a combination of several of these causes (referred to as coupling). The rupture of a specimen under the effect of an impact, its combustion, its dissolution in a solvent, its dilatation under the effect of a temperature variation, its radiolysis or flash photolysis under the effect of intense irradiation are not considered here as ageing, as they are either reversible or rapid phenomena and therefore do not pose any problem in predicting service life.

It may be useful to distinguish between physical aging and chemical aging. In the first case, there is no alteration of the chemical structure of the macromolecules, only their spatial configuration or the composition of the material. In the second case, the chemical structure of the macromolecules is altered. The main cases encountered in practice can be classified according to the table 1 .