Preparation, Structure, Electrically Conducting Behavior And Its Mechanism Of Graphite Filled Polyethylene Based Nanocomposites

The research and development of polymer nanocomposites and their functionalization are one of the forefronts and important subjects in the field of materials science and engineering. In this work, the novel electrically conductive nanocomposites were prepared, which were composed of polyethylene (PE), maleic anhydride grafted polyethylene (gPE) and expanded graphite (EG). The influences of preparation method, composition and processing way and condition on electrical properties and their responsive behavior to external field, together with their functional mechanism were investigated. The main results obtained are as follows:1. Electrically conductive gPE/EG nanocomposites were successfully prepared via solution intercalation method. Electrical volume resistivity measurement showed that the percolation threshold (fw,c) of the nanacomposites was nearly a half lower than that of the composites prepared via conventional melt mixing method TEM, SEM and OM observations and XRD analysis proved that gPE has intercalated into the gaps between graphite sheets or flakes of EG and formed a nanocomposite structure and a micro-composite network. The EG particles filled andsupported by gPE (EG-gPE composite particles) have possessed large size and high aspect ratio, which was responsible for the high conductivity of the nanocomposites.2. Electrically conductive PE/gPE/EG nanocomposites were successfully prepared via solution intercalation (A) and its combination with melt mixing (B) methods. The measurement showed that as the weight ratio of gPE to EG (Rw) was 1.5, the fw,cs of the nanocomposites prepared by A and B methods were about 50% and 20% lower than that of the composites prepared by direct melt mixing (C) method, respectively, and about 60% and 30% lower than that of PE/EG control material prepared by C method, respectively. TEM, SEM and OM observations and DSC analysis proved that these nanocomposites have the similar structure characteristics to that of the gPE/EG nanocomposites mentioned above. In the composites prepared by A, B and C methods, the size and aspect ratio of EG-polymer composite particles and the regularity of nanoscale and micronscale compsite structure within particles decreased in proper sequence. The amount of polymer intercalated into interior of EG depended on preparation method and the destroying extent of primary EG particles depended on shearing extent of the materials during preparation are the key factors determining the structure and conductivity of the composites.3. The relationship between and Rw or gPE weight content (Cg) for PE/gPE/EG composites with a given fw prepared by B and C methods was studied. It was found that this relationship exhibited similar percolation feature to that of the relationship at a given It was proved that, at a given fw, the use of gPE and the increase of Rw or Cg were in favor of the formation of EG-polymer composite particles and the increase of their size and aspect ratio. As a result, these particles are easier to approach or contact each other to form conducting path, and then achieve percolation transition. It was pointed out that this effect, which could be named as percolation effect of composite particles, is different from so-called double percolation effect, which means that the electrical conductivity of composites may be improved by the selective localization of conductive filler particles in one phase or at the interface of polymer blends.4. The influences of processing way or condition on the electrical properties of the nanocomposites with Rw=1.5 prepared by B method were investigated. It was proved that kneading parameter and melt-mixing way played important roles in determining the final electrical properties of the nanocomposites. For the nanocomposites prepared by the B method at optimized and non-optimized kneading parameters and by the masterbatch melt extrusion (D) method, their conductibility showed the follow sequence: optimized B method > D method > non-optimized B method. This could be attributed to the fact that as the...