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