Linear low density polyethylene (LLDPE)/clay nanocomposites. Part I: Structural characterization and quantifying clay dispersion by melt rheology

Abstract

In this study, linear low density polyethylene (LLDPE)/clay nanocomposites with various clay content were prepared by melt processing using two different compatibilizers, maleic anhydride grafted polyethylene (PE-g-MA) and oxidized polyethylene (OxPE). Effects of structure and physical properties of the compatibilizers on the clay dispersion and clay amount on the microstructure and physical properties of the nanocomposites were investigated. The OxPE was shown to significantly create interfacial interactions between the polymer phase and clay layers. Rheological behavior of the samples was examined by a dynamic oscillatory rheometry in linear viscoelastic region. Percolation threshold (phi(p)) and corresponding aspect ratio (A(f)) values were determined by analyzing the improvement in storage modulus at low frequency region depending on the clay loading. Lower percolation and higher aspect ratio values were obtained for the sample series prepared with the PE-g-MA than that prepared with the OxPE. Moreover, fractal size of the clay network above the percolation point was determined by the scaling law for physical gelation of colloidal flocks to quantify clay dispersion depending on the compatibilizer structure. It was found that the PE-g-MA yielded better clay dispersion and more exfoliated structure compared to the OxPE. Microstructural characterization of the samples was also characterized by XRD and TEM. (c) 2007 Elsevier Ltd. All rights reserved.