Rheology of LCP/PET Blends at Solid and Molten States of LCP

Liquid crystalline polymer (LCP) and polyethylene terephthalate (PET) were blended in an elastic melt extruder\ud to make samples having different volume fractions of constituent polymers. Shear stress, shear viscosity, first\ud normal stress difference at different shear rates under steady state conditions of these blends were evaluated\ud at two different temperatures 265 and 285˚C. The LCP was in solid state at 265˚C and in melt state at 285˚C and\ud was dispersed in molten matrix of PET at both temperatures. Shear viscosity of blend increased with addition\ud of LCP in PET matrix. A maxima was observed in viscosity versus composition plot. Blends containing more than\ud 50 vol. % of LCP in the blend show higher viscosity as compared to the constituent polymers. First normal stress\ud difference, N1, increased with LCP content in the blend at 285˚C when ploted against shear stress whereas at\ud 265˚C this trend was opposite. The increased value of N1 with shear rate was explained assuming a tendency of\ud asymmetric particles to rotate under velocity gradient of suspending medium. At 285˚C N1 varied with shear\ud stress in two stages. First stage was characterized with high sensitivity of N1 with shear stress, which reduced in\ud second stage on plastic deformation of LCP droplets