The extensional flow behavior of a modified PET/PHB type thermotropic liquid crystal copolyester (LCP80) was studied by using the contraction flow method with a capillary rheometer.The investigation focused on the effects of the extensional strain rate and temperature on the extensional viscosity and Trouton ratio through experimental measurements.The nematic texture variation and molecular orientation during extensional flow at various temperatures were also observed.Experimental results have shown that the entrance pressure losses

which decreased with temperature and increased with the flow rate

were particularly large.The entrance pressure loss reached about 30% of the total pressure drop even at L/D=50

which was significantly larger than that of conventional polymers.It meant that the end correction in the capillary rheometer could not be omitted even when a long capillary is used.In the entrance pressure loss the extensional component was dominant and the shear component was less than 4% in all cases.This was attributed to the orientation development due to extensional flow as the polymer flew through the comverging entry section

which was confirmed by the macroscopic ordered texture development after extension.At extensional strain rates from 1 to 100 s-1

LCP80 exhibited extension thinning

this phenomenon was more obvious at temperatures above 300℃ due to the increased orientation ability of the rigid molecule chains.The extensional viscosity and the shear viscocity both could be empirically described by the power law model at various temperatures

but the model parameters were quite different.Besides

the Trouton ratios

decreasing with the temperature and extensional rate

were always much greater than the Newtonian values

indicating a high elasticity of the LCP80 melt. The above rheological properties were explained according to the texture observation.