Temperature‐independent viscosity characteristics of polymer systems

Abstract

The possibility of construction of temperature‐independent viscosity characteristics of polymer systems by means of a “reduced variables” method similar to that of Ferry is discussed. It is stated that the viscosity as a function of temperature and shear rate can generally be regarded as the product of two functions, one of which depends only on the temperature and the other only on the shear rate. It is shown by dimension analysis and by assuming the flow of polymer systems to be viscoelastic in nature, that the ratio of apparent viscosity to initial Newtonian viscosity is a temperature‐independent function of the product of the shear rate by the initial Newtonian viscosity. Hence, the latter (observed at shear rates tending to zero) appears to be a most important physical parameter governing the flow properties of polymer systems. At sufficiently low shear rates the apparent viscosity was found to be an exponential function of shear stress, so that the initial Newtonian viscosity can be determined by extrapolation. The above theoretical considerations were checked for the most reliable published data on the flow properties of condensed polymer systems over a wide range of shear rates and temperatures. Experimental results obtained for polymer systems of different nature can be represented satisfactorily by corresponding temperature‐independent viscosity curves.