Study On Preparation Methods Of Expanded Graphite And Graphite Nanosheets And Improvement Of Electrical Conductivity,thermal Conductivity And Electromagnetic Interference Shielding Efficiency

In this paper,the preparation and application of expanded graphite and graphite nanosheets are studied.（1）The expanded graphite was prepared by thermal expansion method,and the prepared expanded graphite was treated by sand-milling method to obtain graphite nanosheets,and then the improvement of the conductivity of the expanded graphite and graphite nanosheets on the polyester film was studied.（2）Different sizes of graphite nanosheets were successfully obtained by stripping the expanded graphite by sand milling and exposing the new exposed surface.The conductivity,thermal conductivity and electromagnetic shielding properties of the obtained graphite nanosheets were studied.（3）The differences of Ca（ClO）₂,K₂FeO₄ and HNO₃in the oxidation intercalation of expanded graphite were studied by thermal expansion method,and the expanded graphite was successfully prepared and the expansion effects were compared.The best oxidized expanded graphite was sanded to prepare graphite nanosheets,and the conductivity of graphite nanosheets was studied.The experiments related to this paper are as follows:Experiment 1:expanded graphite and graphite nanosheets were facilely prepared by the thermal expansion of expandable graphite at 800℃and sand milling of expanded graphite in water,respectively.When the expandable graphite precursor was prepared by the oxidation and intercalation of natural graphite（5 g）using KMn O₄（6 g）as an oxidant in a concentrated sulfuric acid solution（120 m L）at room temperature（25℃）for 8 h,the expanded graphite with a maximum volume ratio of 317 m L g^–1 was prepared after the thermal expansion of the expandable graphite precursor at 800℃for 60 s.The oxidation extent of natural graphite by KMn O₄ is crucial for the preparation of expanded graphite.The thicknesses of graphite nanosheets decreased from 8.9 to 3.2 nm when the sand milling time of the expanded graphite in deionized water was prolonged from 6 to 24 h.The prolonging of the sand milling time not only decreased the layer number of the graphite nanosheet but also increased the d₀₀₂ spacing due to the shocking and shearing forces.The addition of the expanded graphite powder and graphite nanosheets in a polyester paint efficiently improved the electric conductivities of the resultant polyester composite coating films.Experiment 2:a graphite nanosheets polyester film with excellent electric conductivity,thermal conductivity and electromagnetic interference（EMI）shielding efficiency（SE）performance,readily available way,environment friendly style is presented in this paper.The two-dimensional graphite nanosheets have a unique lamellar nanostructure,which makes it have superior performance in the transfer of electricity and heat.In this paper,we used sand milling equipment to prepare graphite nanosheets in water,and used it to improve the electrical and thermal performance of polyester.FE-SEM,TEM,HRTEM,XRD,Raman Spectra and BET were used to characterize the graphite nanosheets,and the electrical and thermal conductivity properties of the nanocomposite were tested.The addition of graphite nanosheets has a significant change in EMI SE,especially 5nm graphite nanosheets that milled for 96 h,when the addition amount is 40%,EMI SE reaches 8.40 d B.Experiment 3:The difference of Ca（ClO）₂,K₂FeO₄ and HNO₃ in the oxidation intercalation of expanded graphite was studied by thermal expansion method.The effect of temperature on the oxidation effect was studied when different oxidants were used to prepare expanded graphite.It was found that the oxidation effect was not good at 0℃,and the strong oxidation effect at high temperature was not conducive to the intercalation of sulfuric acid molecules.The expanded graphite was successfully prepared at 30℃and its expansion effects were compared under different conditions.Expanded graphite was reacted with Ca（ClO）₂（5 g）in concentrated sulfuric acid solution（100 m L）for 6 h,and K₂FeO₄（5 g）in concentrated sulfuric acid solution（100 m L）for 6h.Graphite nanosheets were prepared by sanding expanded graphite with HNO₃（10 m L）in concentrated sulfuric acid solution（90 m L）for 6h,and the electrical conductivity of graphite nanosheets was studied.