Abstract:

The mechanical properties of some amorphous materials can be described in terms of a modified anelastic element (MAE). The characteristics of this element, developed in a previous publication, are extended in order to describe the mechanical behaviour of linear viscoelastic liquids. This treatment leads to the modified standard linear liquid (MSLL). Through this phenomenological model the quasi‐static and dynamic moduli or compliances of viscoelastic liquids can be analytically expressed as a function of time or frequency. The parameters involved in the equations – γ, t0 or ω0, and η0 – are related to the width and the mean characteristic time of the relaxation or retardation spectrum and to the zero‐shear‐rate viscosity of the specimen. A procedure to determine the parameters of the MSLL from dynamical properties is proposed. It is applied to measurements in molten polypropylene (PP) given in the literature, and the results are discussed. Moreover, since the shape of the spectrum associated to the MSLL is quite similar to the well‐known log‐normal distribution function, also a comparison is done. Copyright © 1994 WILEY‐VCH Verlag GmbH & Co. KGaA