Comparison of the Rheological Behavior of Iso- and Syndiotactic Polypropylenes

The rheological behavior of iso- and syndiotactic polypropylenes (iPP and sPP) for two different temperatures of 175 and 190˚C at atmospheric pressure is analyzed employing the Yahsi-Dinc-Tav (YDT) non-Newtonian viscosity model. The predicted viscosity with shear rates of 0.093 to 93.91 s-1 on PPs is compared with the corresponding estimations from the Cross-like model. The obtained results from the YDT model deviate from the reported experimental observations with 1.041 for iPP and 1.86 for sPP. From the zero shear viscosity correlation to temperature- and vacancy fraction- dependent thermo-occupancy function, Yh = Yh(h, T), viscosity parameters were ascertained and associated with polymer tacticity. From the zero shear viscosity relation, an increase in Yh = Yh(h, T) function and hole fraction loss results in increased viscosity. The dependence of the derivative of logarithm of viscosity (viscoholibility) on vacancy fraction, as a function of pressure and temperature, h=h(P,T), procured from Simha-Somcynsky hole theory displays an exponentially decreasing behavior.