Rheological and barrier properties of nanocomposites of HDPE and exfoliated Montmorillonite

Abstract

Polyethylene (PE) / clay nanocomposites were prepared by melt mixing using polyethylene grafted with maleic anhydride (PEg) as compatibilizer. Concentrations between 2 and 15 wt% of an organophilic montmorillonite (MMT) and concentration ratios of 1:1, 2:1 and 3:1 of PEg/MMT were employed. The materials were characterized using X-ray diffraction, scanning electron microscopy (SEM) and thermogravimetry. The SEM images show that the presence of PEg gives place to a large degree of exfoliation at all clay concentrations. For 5 wt% MMT, the best degree of exfoliation is obtained for a 2:1 ratio of PEg/MMT. This ratio also gives place to the largest increase of the elastic modulus, mainly at low frequencies, with respect to that of the corresponding matrix. As the clay concentration increases, for a 2:1 ratio of PEg/MMT, the dynamic moduli increases showing pseudo solid-like behavior at clay concentrations higher than 8 wt%. Moreover, the nanocomposites show rheological properties that are affected by annealing at 200°C signaling further exfoliation or improved platelet and tactoid distributions. The oxygen permeability of PE gradually decreases with clay concentration, reaching a maximum reduction of ~30% for 15 wt% MMT.