Influence of organic intercalants on the morphology and dielectric properties of XLPE/montmorillonite nanocomposite dielectrics

The organic montmorillonite (OMMT) particles treated by two organic intercalants (octadecyl quaternary ammonium salt and double octadecyl benzyl quaternary ammonium salt) were melting blended with crosslinked polyethylene to prepare the nanocomposites. X-ray diffractometer (XRD) was carried out to characterize the influence of organic intercalants on the structure and dispersion of OMMT. The results showed that the octadecyl quaternary ammonium salt could significantly enlarge the interlayer spacing of MMT and promote the intercalation of polymer in OMMT. The double octadecyl benzyl quaternary ammonium salt also enlarged the interlayer spacing of MMT, but contributed little to the intercalation of polymer in OMMT. Differential scanning calorimetry (DSC) and scanning electronic microscope (SEM) analysis was performed to determine the influence of organic intercalants on the crystalline morphology of XLPE/OMMT. The results indicated that MMT particles treated by two intercalants acted as the nucleating agent for the polymer by increasing the grain number and reducing the grain size. The dielectric spectra of XLPE/OMMT nanocomposites treated by different intercalants displayed distinct characteristics. The loss peak was monopeak when the OMMT was treated by octadecyl quaternary ammonium salt, which is shown OMMT1 compatible with matrix resin. However, double peaks were observed when the OMMT was treated by double octadecyl benzyl quaternary ammonium salt, which indicates the polyethylene molecules only few insert OMMT2 lamella and the big long molecular chain introducing by intercalating agent distribute outside the lamella.