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Various aspects of the rheological behaviour of liquid crystalline copolyesters

i.e.

samples of copoly （p-hydroxybenzoate / bisphenol A terephthalate）

were explored by usingInstron capillary rheometer. The experimental results indicated that the apparent viscositywas affected significantly by shear rate

melt temperature and p-hydroxybenzoate unit con-tent. The flow activation energies △E

η

are in the range of 205.1 to 74.5 kJ/mol

dependingon the shear rate of 10-1000 s

-1

at temperature 568-603K. These copolyesters exhibit ayield phenomenon in the shear flow

and the values of yield stress decrease with increasingtemperature. It is quite unusual that the extrudate of the copolyester shows the smallerswelling ratio even than unity at the lower temperature and lower shear rates.