Some new operational modes and parameters of stress relaxation for the viscoelastic characterization of solid polymers. III. The area ratio mode and the intrinsic “strain–clock” function

Abstract

AbstractThe introduced area ratio mode of operation with its corresponding parameters seems to have a fairly high sensitivity to the viscoelastic response of the solid polymer. This appeared from the fact that a good distinction among the linear viscoelastic, the nonlinear viscoelastic, and the viscoplastic ranges of behavior can be made. By using a relevant rheological modeling and its corresponding algorithmical approach, in the case of isotactic polypropylene, this material can be characterized as a morphological three‐phase material consisting of an intraspherulitic crystalline, an amorphous phase, and a interspherulitic para‐crystalline phase. In this sense, the material was simulated using two models: the Poynting–Thomson and the Maxwell–Wierchert, from where a good response of the material to the first model appeared. The so‐called intrinsic “strain–clock” function and its corresponding coefficient of strength of nonlinear viscoelastic behavior, which were relieved by the experimental data, seem to be some powerful and very practical “tools” that can give a proven suplementary characterization of the material. Finally, by this intrinsic function, the existence of permanent internal stresses, was confirmed, in an indirect way, which was mentioned in part II of this study. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 149–158, 2003