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

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 nano- composite did not show the strain hardening, compati- bilized 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 ελ_max ≥ 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.