Preparation And Properties Of Graphite Nanosheet And Its Polyethylene Based Composites

Polyethylene based nano-composites have been widely concerned, which isbased on the improvement of nanoparticles on mechanical and dielectricproperties of the polyethylene. Due to the unique performance of nano-graphitematerials (like graphite) on electrical properties, mechanical proerties, etc., newways and means for nano-composites is expected to improve the properties ofpolyethylene. Here, based on preparation of graphite nanosheets, the mechanicaland electrical properties of polyethylene/graphite nanosheets composite materialshave been investigated, and the influence of exfoliation and structure factors ofgraphite sheets on properties of nanocomposites haven discussed.In this thesis, expanded graphite was used as raw material and graphitenanosheets were prepared by ultrasonic wave and ball-milling. The compositeswere prepared by using melt blending and solution blending polyethylene. Thestructure of graphite nanosheets were characterized by X-ray diffraction (XRD),scanning electron microscope (SEM) and transmission electron microscopy(TEM). The mechanical properties of composite materials were evaluated bytensile strength and fracture elongation. The electric properties of compositematerials were evaluated by volume resistivity, dielectric constant and dielectricloss.The results show that the thickness of graphite nanosheets, which wereprepared by ultrasonic wave or ball-milling method using expanded graphite asraw material, was out10nm. Comparing this two methods, ultrasonic wavemethod can obtain graphite nanosheets with lager surface area, while ball-millingmethod induced graphite nanosheets with smaller surface area than ultrasonicwave method. Using the melting method or solution blending fabricated PE/BGNcomposites have different nano-graphite dispersion. The dispersibility of graphitenanosheets in composites by ball-milling method is better than that of ball- milling method, which results in good mechanical properties. Related to and bothpreparation methods of graphite nanosheets and graphite dosage have effect onproperties of composite. Ultrasonic wave method has significant influence onproperties of composites. When the graphite nanosheets content was4.00wt.%,the performance of the composite changed significantly, which indicated that thestate of graphite nanosheets in composites changed from isolated dispersion toaggregation state.