Stress relaxation after steady shearing: Applications and empirical representation

Abstract

synopsisThe measurement of stresss relaxation following steady-state shearing is particularly useful in the terminal relaxation zone, where the rheological properties are molecular weight dependent. This paper contains a description of the method as applied to molten polymers, and an empirical function found to be useful for fitting the data. Three examples are given to demonstrate some direct and simple applications. First, the decrease of viscosity with increasing shear rate may be estimated by simply replotting the experimental data. Second, extrapolation of calculated viscosities to very high shear rates is shown to lead to a possible explanation for melt fracture. Third, the true Newtonian viscosity can be estimated from measurements conducted at a nonzero shear rate.

The measurement of melt stress relaxation in the Weissenberg Rheogoniometer

“…It seems probable that published relaxation data are not completely free of the effects described above (3,4,5). The methods of measuring torque are similar in principle to that used in the Rheogoniometer, and presumably are open to similar criticism.…”

Some viscoelastic porperties of poly(vinyl chloride)/dioctyl phthalate systems

“…The experiment can be carried out on a cone-plate or a coaxial cylinder system of commercial rotational rheometers. This method has been applied in order to study the viscoelastic response of polymeric fluids as polystyrene solutions (1 to 3) polyisobutylene solutions (l), (4), polyacrylamide solutions (4) and polyisobutylene melts (4), polystyrene melts (5,6), and polyethylene melts (5,7).…”