Rheological Behaviour of a Thermotropic Liquid Crystal Copolyester: Hydroxybenzoic Acid / 2,6-Hydroxynaphthoic Acid (Hba/Hna)

Abstract

The rheology of the all-aromatic copolyester thermotropic liquid crystal 73/27 HBA-HNA has been studied over a large interval of shear rates. At small shear rates the transient behavior has been analyzed with a cone and plate rheometer. The shear stress and the first normal stress difference have been found to scale with the strain. Steady values for both viscosity and first normal stress difference have been obtained. The steady shear viscosities have been correlated to capillary data at higher shear rates. Three zones can be found in the steady viscosity vs shear rate curve: a shear thinning region at small shear rates, an almost newtonian region, and a second power-law region at higher shear rates. In the shear rate interval studied with the cone and plate rheometer the steady first normal stress difference remains positive.