Role of Solvent Nature on Rheological Properties of Nylon 6,6 Solutions

Abstract

The rheological properties of concentrated solutions of nylon 6,6 of various molecular weights in various solvents have been determined in steady shear flow. Four solvents including 90% formic acid, m‐cresol, 97% H2SO4, and 100% H2SO4 were selected based on their effect on the ionic nature of nylon 6,6 in dilute solutions. The magnitude of the rheological properties of concentrated solutions depended on the solvent when compared at the same shear rate (γ̇) and segment contact parameter (cM̄w, where c is the concentration and M̄w is the weight average molecular weight). However, as observed by others, the critical value of cM̄w for the onset of entanglements was independent of the solvent. The contact parameter was effective in reducing values of η0 versus cM̄w to a single curve for three of the solvents but values of η0 for formic acid solutions were consistently two orders of magnitude lower than for the other solutions. Values of the equilibrium compliance, Je0, were highest for the formic acid solutions. However values of the reduced compliance (JeR) for all four solutions were around 0.4 which is in reasonable agreement with the Rouse theory. The onset of non‐Newtonian viscosity depended on the solvent but the shape of the flow curves was similar for all polymer/solvent systems. It is concluded that the solvent viscosity may contribute more to the rheological properties of concentrated solutions than the solvent's influence on the ionic nature of polymer chains.