Compatibilization of HDPE/organoclay nanocomposites by functionalized polyethylenes

High density polyethylene (HDPE)/organoclay nanocomposites have been prepared by melt compounding, using three functionalized polyethylene compatibilizers: two of them prepared from HDPE by grafting with maleic anhydride (HDMA) and acrylic acid (HDAA), and one produced by radical copolymerization of ethylene and acrylic acid (EAA). The nanofiller was a commercial clay, Cloisite® 15A (15A). Preliminary DSC and POM investigation of 50/50 w/w blends of HDPE with the three compatibilizers showed that HDMA and, probably, HDAA are miscible with HDPE in the solid state, whereas EAA is not. The nanocomposites with an HDPE/compatibilizer ratio of 88/12 and 3 phr of clay (inorganic content) were prepared from concentrated compatibilizer/clay masters containing 25 phr of clay by dilution with HDPE and characterized by XRD and TEM, and by rheological tests. HDMA leads to almost complete exfoliation of 15A in nanocomposites with 3 phr of clay. However, the XRD pattern of the relevant master with 25 phr of 15A displays an interlayer spacing close to that of the clay, probably due to the low functionalization degree of this material. On the contrary, both EAA and HDAA lead to mixed exfoliated and intercalated morphologies, with basal d001-spacings of ~4.3 and ~3.4 nm, respectively, independent of clay concentration, though the intensity of the reflection increases strongly with an increase of the filler content. The ternary HDPE/compatibilizer/15A nanocomposites with 88/12/3 composition were shown to be essentially intercalated by XRD and TEM. Their rheological characterization demonstrated that the addition of 15A to the HDPE/compatibilizer blends brings about an increase of viscosity, especially at low frequencies, which is more evident for the nanocomposite compatibilized with HDMA. The morphology and the rheological properties of the three nanocomposites are discussed with reference to the structure of the functionalized polyethylenes used as compatibilizers and to the chemistry of their interactions with the 15A clay.