| Due to high impact strength, corrosion resistance, low density, and the price is often lower than the metal material, thermoplastics have the potential to replace the metal in many applications. But the polymer is electrically insulating material, which limits its application in the field of conductive material. The addition of carbon black and graphite as conductive fillers in polymers often require high content to meet the electrical property requirements, but high filler content will cause great damage to the mechanical properties of composite materials. In recent years, graphene is used as conductive filler for the preparation of conductive polymer composites has become a research hotspot. Graphene added to the polymer, will inevitably cause the graphene layers folding, stacking and aggregation, which greatly reduces 2D specific surface area of the graphene. This paper selects one of the five general plastics polypropylene(PP) and graphene nanoplatelets(GNP). To study the use of a twin screw extruder to mix polypropylene and GNP with high-speed shear, which can improve the dispersion of GNP in PP matrix. The third chapter lays the basis for the following two chapters. By studying the influence of GNP flake sizes and content on the properties of the nanocomposites. The fourth and fifth Chapter by studying the different processing flow field will change the microstructure and mophology of the nanocomposites, to explore the effect of GNP dispersion in the PP matrix on the conductivity and mechanical properties of the nanocomposites. Preparation of multifunction and high performance PP/GNP nanocomposites, can be used as electromagnetic shielding, radio shielding and anti-electrostatic interference materials in electronics, aerospace and other fields, has a very broad application.The specific contents are as follows:(1) Four kinds of PP/GNP nanocomposites with different GNP sizes were prepared by melt blending, the microstructure and crystallization behavior of nanocomposites were studied. Their thermal and electrical conductivity, mechanical properties were also investigated, providing a theoretical basis for the material selection of GNP. Field emission scanning electron microscopy (FESEM) images were closely related to the structure of the nanocomposites and their properties. It was found that the flake size of 40μm GNP most easily formed conductive network in the PP matrix, the corresponding nanocomposites exhibit thermal conductivity of the best and maintain good mechanical properties at the same time.(2) The influence of GNP content on the properties of PP/GNP nanocomposites were studied. It was found that when GNP were low, the GNP were dispersed uniformly, and there was less agglomeration. When the GNP content increased to 7%, the conductive network formation in PP matrix, the conductivity of the nanocomposites increased dramatically. When the GNP content were high, the agglomeration of GNP was severe.(3) Shear stress can not only affect the morphology of the dispersed phase, but also can control the interface morphology of the two phases. In order to further improve the dispersion of GNP in the PP matrix, the effects of the screw speed and screw configuration on the morphology-properties of the nanocomposites were studied. The results showed that the composites have the best performance under the medium screw speed. Moreover, increased kneading block on the screw configuration can improve the dispersion of GNP in PP matrix, and further improve the properties of nanocomposites.(4) By the method of installing ultrasonic instrument on the extrusion die of the rheometer, the effects of ultrasonic vibration on the rheological properties of PP/GNP nanocomposites were studied. It was found that under low shear rate, ultrasonic vibration can reduce the melt viscosity and die pressure and improve the dispersion of GNP in the PP matrix, improve the degrees of crystallinity of the composites. |
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