Temperature and shear dependencies of rheology of poly(acrylonitrile-co-itaconic acid) dope in DMF

Abstract

Poly(acrylonitrile-co-itaconic acid) (poly(AN-co-IA)) precursor required for carbon fiber production is made into a dope and spun into fibers using a suitable spinning technique. The viscosity of the resin dope is decided by the polymer concentration, polymer molecular weight, temperature, and shear force. The shear rheology of concentrated poly(AN-co-IA) polymer solutions in N,N-dimethylformamide (DMF), in the M̄v range of 1×105-1×106 g mol-1, has been investigated in the shear rate (γ') range of 1×101-5×104 min-1. The zero shear viscosity (η0) has been evaluated at different temperatures. The temperature dependence of zero shear viscosity conformed to the Arrhenius-Frenkel-Eyring model. The free energy of activation of viscous flow (ΔGV) values were in the range 5-32 kJ mol-1 and this value increased with increase in polymer concentration and molecular weight. A master equation for the ΔGV value of the polymer solution of any M̄ v and concentration (c) is suggested. The power law (τ = kγn) fitted well for the shear dependency of viscosity of these polymer solutions. The pseudoplasticity index (n) diminished with increase in polymer concentration and molecular weight. An empirical relation between viscosity (η) and M̄v was found to exist at constant shear rate, concentration and temperature. For each M̄v, the equation relating n, c, and T was established. Copyright © 2008 John Wiley & Sons, Ltd.