Rheological properties of liquid crystalline copoly (p-hydroxybenzoate/bisphenol A terephthalate)

Various aspects of the rheological behaviour of liquid crystalline copolyesters, i.e., samples of copoly (p-hydroxybenzoate/bisphenol A terephthalate), were explored by using Instron capillary rheometer. The experimental results indicated that the apparent viscosity was affected significantly by shear rate, melt temperature and p-hydroxybenzoate unit content. The flow activation energies Delta E(eta) are in the range of 205.1 to 74.5 kJ/mol, depending on the shear rate of 10-1000 s(-1), at temperature 568-603K. These copolyesters exhibit a yield phenomenon in the shear flow, and the values of yield stress decrease with increasing temperature. It is quite unusual that the extrudate of the copolyester shows the smaller swelling ratio even than unity at the lower temperature and lower shear rates.