REVIEW ON PHYSICAL AGING OF POLYMERIC MATERIALS.

It is well known that amorphous glassy polymers continue to undergo a physical aging process in which the enthalpy, entropy, volume and the characteristic relaxation time continue to change. At temperatures well below the glass transition temperature, the equilibrium state is never reached. The viscoelastic properties are affected by the extent of such an aging process. Several thermodynamic models are reviewed and mechanical, volumetric and dielectric data are compared. How to predict the complex time dependent mechanical properties is illustrated. The knowledge gained by the study of the aging phenomenon is shown to be useful for the prediction of the curing reaction process of thermosetting polymers such as epoxy resins.