Stress cracking in surfactant media
Physical aging of polymer materials

To the best of our knowledge, this phenomenon has only been observed in the case of polyethylene; it can easily be demonstrated using the experiment shown in figure 21 .

After a time dependent on experimental conditions, but considerably shorter than in the case of exposure to air, a crack is observed in the most stressed zone (convex part). The service life can be conventionally defined as the time after which 50% of the specimens (identical, exposed under identical conditions) have failed.

This phenomenon remained unexplained for a long time, as it soon became apparent that the liquid did not penetrate the polymer, and that solvent absorption was therefore not involved.

Sustained research...