Rheology of LCP/PET blends at solid and molten states of LCP

Abstract

Liquid crystalline polymer (LCP) and polyethylene terephthalate (PET) were blended in an elastic melt extruder to make samples having different volume fractions of constituent polymers. Shear stress, shear viscosity, first normal stress difference at different shear rates under steady state conditions of these blends were evaluated at two different temperatures 265 and 285 degrees C. The LCP was in solid state at 265 degrees C and in melt state at 285 degrees C and was dispersed in molten matrix of PET at both temperatures. Shear viscosity of blend increased with addition of LCP in PET matrix. A maxima was observed in viscosity versus composition plot. Blends containing more than 50 vol. % of LCP in the blend show higher viscosity as compared to the constituent polymers. First normal stress difference, N-1, increased with LCP content in the blend at 285 degrees C when ploted against shear stress whereas at 265 degrees C this trend was opposite. The increased value of N-1 with shear rate was explained assuming a tendency of asymmetric particles to rotate under velocity gradient of suspending medium. At 285 degrees C N, varied with shear stress in two stages. First stage was characterized with high sensitivity of N, with shear stress, which reduced in second stage on plastic deformation of LCP droplets.