Morphology and crystallisation kinetics of polyethylene / montmorillonite nanocomposites

In recent years, the engineering community has taken huge interest in nanocomposites. That is, systems in which an additive is dispersed on a characteristic level of a few nanometres. Previous research has established that nanostructuration of polyethylene (PE) with montmorillonite (MMT) affects both the nucleation density and growth behaviour of the host matrix. The inorganic MMT must be modified chemically in order to interact with the PE and become adequately dispersed. The MMT / PE interface will therefore influence the morphology (and hence the macroscopic material behaviour) by virtue of its massive specific surface area. A masterbatch system containing -40% MMT in a branched PE matrix was chosen because of its apparently minimal nucleating action. Subtle morphological features would thereby be more easily observed. The masterbatch was dispersed by single screw extrusion into blends containing 90 parts branched to 10 parts linear polyethylene. Such blends were used in order to obtain well-defined morphologies for scanning electron microscopy. The masterbatch was added at 3 loading levels: 4.76%, 9.09% and 16.7% by mass. Wide-angle X-ray scattering was unable to detect any undispersed clay. We report on the effect of clay loading level on the isothermal crystallisation characteristics and morphologies, as determined by differential scanning calorimetry and scanning electron micrography. AC ramp breakdown data are discussed in the light of these observations.