MECHANICAL-BEHAVIOR OF LINEAR VISCOELASTIC LIQUIDS

The mechanical properties of some amorphous materials can be described in terms of a modified anelastic element (MAE). The characteristics o f this element, developed in a previous publication, are extended in o rder to describe the mechanical behaviour of linear viscoelastic liqui ds. This treatment leads to the modified standard linear liquid (MSLL) . Through this phenomenological model the quasi-static and dynamic mod uli or compliances of viscoelastic liquids can be analytically express ed as a function of time or frequency. The parameters involved in the equations - gamma, t(0) or omega(0), and eta(0) are related to the wid th and the mean characteristic time of the relaxation or retardation s pectrum and to the zero-shear-rate viscosity of the specimen. A proced ure 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, si nce 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.