Shear-induced crystallization of isotactic polypropylene based nanocomposites with montmorillonite

Abstract : Shear-induced isothermal crystallization in iPP based nanocomposites with organo-modified montmorillonite was followed by light depolarization technique. Prior to the crystallization, samples were sheared at 1 or 2 s(-1) for 10s in a plate-plate system at crystallization temperature of 136 degrees C. Structure of the solidified specimens was investigated by light microscopy and electron microscopy, X-ray techniques and IR spectroscopy. Strong enhancement of the nucleation and crystallization after shearing was observed in the compatibilized nanocomposites with the clay. Clay exfoliation was found to accelerate strongly the shear-induced nucleation and overall crystallization. However, the sheared samples exhibited only weak orientation of alpha crystals with (040) crystallographic planes parallel to shearing direction that resulted probably from a small population of oriented crystals that formed due to shear-induced orientation of iPP chains and served as nuclei for further nearly isotropic growth.