Study on rheological behavior of polypropylene/clay nanocomposites

Polypropylene/montmorillonite nanocomposites (PPCN) were prepared by melt intercalation with maleic anhydride modified low isotactic polypropylene as the compatibilizer. The linear and nonlinear rheological properties of polypropylene/montmorillonite nanocomposites were studied. The deviation from linear behavior occurred at a strain of 100 that was quite less than that for the polymer matrix. The results of dynamic frequency scan showed that the percolation threshold of PPCN was near 3 wt%. Having been subjected to steady preshear, the tactoids could be oriented preferentially in the shear direction, and the percolation network was ruptured. The magnitudes of the stress overshoots observed in the reverse flow experiments were strongly dependent on the rest time, which indicated that the ruptured network could be reorganized even under quiescent conditions. Furthermore, PPCN displayed a strain-scaling stress response to the Startup of steady shear. The maxima of the stress overshoots appeared at the stain of 10degrees, which was consistent with the strain where the deviation of linear viscoelastic behavior started. It might imply that subjected to the deformation less than 10degrees, the network structure could be regard as elastic one. Additionally, the analogous strain-scaling stress response to the startup steady shear elucidated the structural analogy between PPCN and liquid crystal polymer solution. (C) 2003 Wiley Periodicals, Inc.