Viscoelastic Properties of Concentrated Solutions of Polyvinyl Alcohol

Abstract

The dynamic viscosity and rigidity of concentrated solutions of polyvinyl alcohol samples having different molecular weights have been measured by means of a torsionally oscillating rheometer and an electromagnetic transducer within the ranges of frequencies from 0.08 to 400 cps and the temperature range from 20° to 55°C. The solutions behave almost as Newtonian liquids at lower frequencies; however, at the frequencies around 1 to 10 cps the viscosity of solutions begins to decrease while the rigidity increases rapidly. The frequency at which the rather abrupt change in dynamic viscosity and rigidity takes place is lower the higher the concentration, the higher the molecular weight, and the lower the temperature. The effects of the concentration, temperature, and molecular weight on the zero shear (frequency) viscosity have been examined quantitatively, and some of characteristic features observed on other high polymers have also been found. Comparison of the dynamic voscosity with the steady-flow viscosity shows that the frequency dependence of dynamic viscosity is not quite quantitatively equivalent to the rate of shear dependence of steady-flow viscosity. The dynamic data have also been compared with two molecular theories of viscoelastic behavior of high polymers, and showed rather good agreement. A slight discrepancy observed in this comparison may be attributed to the molecular weight distribution in the sample and intermolecular interlacings in the concentrated solution.