Concentration Dependence of Rheology for Poly(vinyl Acetate) Solutions

Abstract

The rheology of a poly(vinyl acetate) (PVAc) of Mw=1.75×106,Mw/Mn=6.0, and Bn(long branches/molecule)=3.2 in diethyl phthalate and benzyl alcohol solutions has been investigated at concentration of 0.01–0.20 g/ml. The low shear‐rate viscosities, first normal stress differences, dynamic viscosities and moduli were measured by a mechanical spectrometer and the high shear values were obtained by a concentric‐cylinder viscometer. Consistent with the stress trend, it was observed that at lower concentration and higher temperature, non‐Newtonian effects occurred at higher shear rate and that the variation in viscosity with shear rate was greater at higher concentration. Solvent effects were found important even in concentrated solutions with the increase in viscosity with concentration more in diethyl phthalate than in a better solvent, benzyl alcohol. The critical concentration at which “entanglement” occurs was estimated to be ∼0.05 g/ml in both solvents. The viscosity data superimposed on a Graeasley vis...