Characterisation of an Industrial Polymer Melt Through Either Uniaxial Extension or Exponential Shear Data: An Application of the Pom-Pom Model

Abstract

We present new non-linear data in extension and two different shear histories. These data are used to compare the effectiveness of using exponential shear data and uniaxial extension data to characterise the non-linear response of an industrial LDPE melt with the pom-pom molecular model. We conclude that extension and exponential shear both allow good predictions to be made in simple shear. However, the characterisation spectrum obtained from exponential shear data fails to predict the correct degree of strain hardening at low extension rates. From this study we are able to suggest circumstances under which exponential shear provides a useful characterisation of branched polymer melts.

Rheology and Rheological Measurements

“…The study of the viscosity of polymer melts (46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57) is important for the manufacturer who must supply suitable materials and for the fabrication engineer who must select polymers and fabrication methods. Thus, melt viscosity as a function of temperature, pressure, rate of flow, and polymer molecular weight and structure is of considerable practical importance.…”

“…A number of experimental methods have been applied to measure the melt viscosity of polymers (51)(52)(53)(54)(55)(56)(57)(58)(59)(60), but capillary extrusion techniques probably are generally preferred. Rotational methods are also used, and some permit the measurement of normal stress effects resulting from elasticity as well as of viscosity.…”