Dispersion Of Graphite Nanosheets In Polymer Resin Via Masterbatch Blending And The Structure And Properties Of The Nanocomposites

In this study, graphite nanosheets (GN) were modified with AS resin (acrylonitrile-styrene copolymer) to make AS-modified GN masterbatch. The masterbatch was successfully dispersed in polymer matrices via extrusion process. An effective approach of fabrication of polymer/graphite nanosheets composites through masterbatch blending was carried out.Graphite nanosheets possess high aspect ratio (about 240), with 30-80nm in thickness and 5-20 urn in diameter. This kind of isolated graphite sheets could be more readily dispersed into the polymer matrices and more easily to form continuous conducting networks. With thickness in nanoscale, however, GN are likely to accumulate from each other, so the uniform dispersion of GN in polymer is hard to obtain. The main object of the thesis is to find an effective method for the homogeneous dispersion of graphite nanosheets in matrices via masterbatch blending.In the study, GN were modified with AS resin by co-deposition to prepare the AS/GN compound masterbatch with high concentration of GN. The masterbatch, in which isolated GN were well-wrapped by AS resin, can effectively prevent GN from aggregations, and greatly stimulate the dispersion of GN in polymer matrices. The results indicated that the masterbatch could be obtained by blending 20wt% of AS resin with 80wt% GN. The GN can be homogeneously dispersed in polymer matrices via the extrusion process. Evidences turned out that the miscibility of masterbatch with matrices play a crucial role in affecting composites percolation threshold. In the thesis, the percolative behavior of AS/GN, PS/GN and HDPE/GN conducting composites prepared by this method were compared and discussed. The dispersed structures of GN in the matrices were characterized.The effect of extrusion times on the electrical properties of the composites was particularly studied in the thesis. It was found that the resistivities of one-time extrusion were always higher than that of repetitious extrusions because of poor dispersion of GN in polymer in the one-time extruded samples. With the increase ofextrusion times, the composites resistivities decreased gradually and reached a relative stable region, indicating that more homogeneous dispersion and more uniform structure were obtained. It reveals that the well-blended polymer/GN could be achieved via a reasonable extruded technology.The percolative range of each composite was successfully concluded by the fluctuation of the resistivities and the ratios of resistivities of one end to the other of the samples. The measurement is an inexpensive, quick and convenient way to characterize the dispersion of GN in matrices and the percolative range of composites.The nonlinear conduction behaviors of HDPE/GN composites depended on ambient pressure and temperature were also studied in the thesis. A notable nonlinear resistance-pressure conduction behavior was found for the nanocomposites prepared by the masterbatch blending, and resistance-temperature conduction behavior as well. The results showed that the filler content play an important role in the positive pressure coefficient (PPC) and positive temperature coefficient (PTC). The PPC and PTC intensities of different GN content were compared. It was found that the PPC and PTC intensities were much stronger if the GN content was near to the percolation threshold.