Structure and morphology of HDPE-g-MA/organoclay nanocomposites: Effects of the preparation procedures

Nanocomposites comprising high density polyethylene (HDPE) or maleic anhydride-grafted HDPE (HDMA) as the host polymers and Cloisite_ 20A (20A) as the organoclay filler were prepared by melt-compounding, solution-blending and static annealing of polymer/clay powder mixtures. The dependence of their structure and morphology on the preparation conditions was studied by X-ray diffraction (XRD and SAXS), polarized optical microscopy (POM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was shown that intercalated nanocomposites based on HDPE or HDMA cannot be obtained by solution-blending, as long as solvent removal is made at room temperature. In fact, wide angle XRD patterns of solution blended composites are similar to those of mechanical blends of clay and polymer. However, as demonstrated by XRD and SAXS, fast intercalation or even complete delamination was obtained when the HDMA composites prepared from solution were annealed statically at temperatures higher than the polymer melting point. This implies that solution-blending causes efficient fragmentation of the clay agglomerates into thin tactoids (though unintercalated) homogeneously dispersed in the polymer matrix. This conclusion, supported by the finding that annealing mechanical blends of polymer and clay powders only leads to intercalated structures, was confirmed by TEM and SEM analyses. Morphology investigation revealed that, in contrast to melt-compounding, solution-blending followed by static annealing fails to produce significant orientation of clay platelets and polymer crystallites. However, repeated compression molding cycles were shown by XRD and SAXS to cause increasing levels of orientation of the platelets and the polymer matrix parallel to the sample flat surface.