Comparative Rheological Properties of Dope Solutions of High Molar-Mass Poly(acrylonitrile-co-itaconic acid) and Poly(acrylonitrile-co-methylacrylate-co-itaconic acid)

Abstract

The rheological behaviour of a dope solution of poly(acrylonitrile-co-itaconic acid) copolymer was compared with that of a poly(acrylonitrile-co-methylacrylate-co-itaconic acid) terpolymer of identical molecular weight. The effects of temperature, concentration and shear force on the rheology of the polymer dope were examined. In both cases, the temperature dependence of zero shear viscosity conformed to the Arrhenius-Frenkel-Eyring equation. The free energy change ΔGv increased with concentration more significantly for the copolymer than the terpolymer. The Power Law model was fitted to the shear dependency of the viscosity, and the pseudoplasticity index (n) decreased with the dope concentration. The shear thinning behaviour was more pronounced for the terpolymer than the copolymer. The decreasing trend of the pseudoplasticity index with concentration and temperature was more pronounced in the case of the terpolymer than the copolymer. Empirical models were arrived at, which could predict the n value of the polymers of a given viscosity-average molecular weight at any concentration and temperature. The onset of shear thinning shifted to a lower shear regime with increase in solid concentration.