Rheological behavior and theoretical modeling of uniaxial elongational flow properties of polypropylene/layered silicate nanocomposites

Abstract Rheological behaviors of polypropylene/layered silicate nanocomposites were investigated in both shear and uniaxial elongational flows. They were analyzed by using the K‐BKZ constitutive equation with two damping functions, for example, the WD‐FÖ and PSM‐LT models in transient and steady elongational viscosities. Although pure PP matrix and uncompatibilized nanocomposite did not show the strain hardening, compatibilized nanocomposite showed outstanding strain‐hardening behavior due to three‐dimensional network structure. Predictions of WD‐FÖ and PSM‐LT models gave good agreement with the experimental results at low elongational rate region. However, the elongational viscosity calculated with the WD‐FÖ model did not predict the steady‐state value and diverged to infinity when $\dot{\varepsilon} {\lambda}_{\bf max}\ {\geq}\ {\bf 1}$. The PSM‐LT model offered good description on transient and steady elongational viscosities even at higher elongational rates as well as on strong strain‐hardening behavior of compatibilized nanocomposites. Through the numerical analysis, using the K‐BKZ model with two types of damping functions, it was found that the PSM‐LT model was superior to that of the WD‐FÖ model in rheological modeling of PP/layered silicate nanocomposites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers