Morphological aspects of injected polypropylene/clay nanocomposite materials



Polypropylene (PP) clay nanocomposites were injection-molded using two different coupling agents based on maleic anhydride-grafted PP (MA-g-PP) and two clay loadings. The morphological aspects of these materials were studied by depth profiling. Molecular chain and clay orientations were characterized using attenuated total reflectance-infrared analysis and transmission electron microscopy (TEM). Both clay platelets and PP molecular chain orientations were found to decrease from the surface toward the core of the injection–molded specimens. Clay intercalation, characterized by both complementary X-ray diffraction and TEM, was found to be significantly influenced by both the characteristics of the coupling agent used and the type of residual stresses generated at each layer across the thickness of the injection-molded parts. The use of low-molecular weight (Mw) MA-g-PP led to a uniform intercalation but with no further exfoliation. The use of higher molecular weight MA-g-PP led to a heterogeneous intercalation with some signs of exfoliation. The crystallization behavior of PP clay nanocomposites studied by differential scanning calorimetry showed an increase in the level of crystallinity from the surface to the core of the specimens; these results were also confirmed by scanning electron microscopy. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers