Effect of pressure on shear viscosity of poly(ethylene terephthalate) melt

The variation of the shear viscosity of poly(ethylene terephthalate)(PET) melt was investigated using the capillary rheometer and counter pressure chamber when the pressure at the outlet of capillary was higher than normal pressure,and it was observed that the shear viscosity of PET was dependent on the average capillary pressure and shear rate,respectively.The results show that when shear rate is fixed constant,the shear viscosity of PET increases with the increase of average capillary pressure,but the increase margin varies with shear rate.The effect of pressure is more prominent at low shear rate.When the average capillary is fixed constant,the shear viscosity of PET decreases with the increase of shear rate,as it is shown by less shearing.It was found by computation that the pressure coefficient of PET at 290 ℃ was about 11.94 GPa-1 when shear rate is fixed constant.