Polypropylene-nanoclay composites under electron irradiation in SEM: Structure, charge trapping and electron emission properties

In this work, polypropylene (PP) and its polymer nanocomposites (PNCs) films containing very low contents (2-6 wt %) of Cloisite 20A natural montmorillonite clay platelets were investigated. In a first, they were characterized by means of several analytical techniques such as X-ray Diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) and UV-visible spectroscopy. Secondly, the nanocomposites are submitted to an electron beam in a Scanning Electron Microscope (SEM) and the induced currents are measured using a time-resolved current method. These currents are used to determine the trapped charge and the electron emission yield. The aim is to contribute to the understanding of the effect of different concentrations of nanoclay platelets on the studied properties by correlating the results obtained by both techniques. The analytical characterization showed that upon the increase of nanoclays concentration an intercalated structure and an increase of crystallinity are induced. On the other hand, the optical band gap energy is modified because the increasing of the density of localized states in the forbidden energy band. As regards the measurement of the trapped charge, it was found, surprisingly, that not only the leakage current increases as a function of clay loading level but also the trapped charge (or the surface potential). This could be related to the increase of conductivity in one hand and to proliferation of interfaces between nanoparticles and neighboring materials on the other hand.