Physical aging of polymer blends

Abstract

The selection of polymers and polymer blends for use as specific materials requires the consideration of how these will withstand the environmental conditions to which these will be subjected. The long-term stability of a polymer will depend on its aging characteristics both physical and chemical. Physical aging is the term used to describe the observed changes in properties of glassy materials as a function of storage time, at a temperature below the glass transition, Tg. This phenomenon is important mainly when the materials have a substantial amorphous content. For these materials, a quench from above Tg into the glassy state introduces a nonequilibriumstructure which, on annealing at constant temperature, approaches an equilibrium state via small-scale relaxation processes in the glassy state. The aging process can be detected through the time evolution of thermodynamic properties such as the specific volume or enthalpy or mechanical methods such as creep, stress-relaxation, and dynamic mechanical measurements. Here, the fundamental principles of physical agingwill be described, and models that quantitatively describe the aging process are briefly described. Physical aging effects have practical implications and need to be considered when assessing the long-term stability of polymers and polymer-polymer mixtures. This chapter focuses on a discussion of the effect of blending on physical aging and gives a review of the different experimental methods that can be used to compare aging rates in blends to those of the individual components.