Phase heterogeneity of melts of a liquid crystalline copolyester and its effect on the rheology and also the structure and mechanical properties of extrudates

Abstract

The kinetics of change in the viscous properties of LC melts of a copolyester containing units of phenyl hydroquinone and terephthalic and p-hydroxybenzoic acids has been studied. Two temperature regions were found in which the rheological properties of the coppolyester significantly differ: at low temperatures continuous rise in viscosity is observed and at high ones viscosity remains constant with time. The copolyesters in the low temperature region are characterized by a viscosity anomaly. The DSC data indicate that the rheological behaviour of the copolyesters at low temperatures is determined by the recrystallization process. The thermal and mechanical prehistory influences the rate of recrystallization. The physicomechanical characteristics of the extrudates of the copolyester improve on passing from the low to the high temperature region of formation. Electron microscopic and X-ray structural investigations point to an improvement in the molecular orientation of the extrudates with rise in temperature. The presence of a crystalline phase in the copolyester melt hampers the orientation and worsens the mechanical characteristics.