Exfoliation And Modification Of Graphite And Hexagonal Boron Nitride And Their Application In Thermally Conductive Polymer Composites

Graphite exhibits excellent properties of electrical conductivity and thermal conductivity because of its unqiue lameller structure.It has been widely used in solar cell,lithium ion battery,super capacitor,cooling materials and polymer materials.The derivatives of graphite,such as graphene,graphite-intercalation-compounds(GIC),also have their unique performances and structures.Graphene has excellent properties of chemical stability,barrier property and thermal conductivity because of its two-dimensional planar structure with one atomic thickness.Synthetizing thermally conductive polymer composites by doping with graphene is an important part of functionalization of polymer composites.Graphite-intercalation-compounds was synthetized and its thermal structure was changed to improve thermal conductivity.Hexagonal boron nitride which is a structural analogue of graphite also has excellent properties of thermostability,antioxidant,low expansion coefficient,low coefficient of friction,chemical stability,thermal conductivity and machinability.In this study,the thermal conductivity of polymer composites was carried out based on exfoliation,modification of graphite and hexagonal boron nitride.The main contents are as follows:(1)Graphene oxide(GO)was synthetized with different oxidation degree by various methods and we studied the thermal conductivity of their polymer composites.In this method,different oxidant mass ratio and different reaction temperature were used to synthetize GO with higher quality and fewer defects in order to improve the thermal conductivity of Grapheme-polyvinyl alcohol film(rGO/PVA).After that,rGO/PVA composites was synthetized by doping high quality graphene and adding montmorillonite(MMT)to improve the thermal conductivity of Montmorillonite-grapheme-polyvinyl alcohol(MMT/rGO/PVA)composites,and finally,the thermal conductivity of MMT/rGO/PVA reached 66.4 W·m-1·K-1.(2)Hexagonal boron nitride(h-BN)was exfoliated by various methods and we studied the thermal conductivity of their polymer composites.h-BN which is a structural analogue of graphite was widely used in insulation and thermal conductive composites because of its high thermal conductivity and insulation performance.h-BN was exfoliated by gas exfoliation method,reductive alkylation stripping method and liquid phase stripping method in order to synthetize modified h-BN with higher dispersibility.After that,we warpped the h-BN with dopamine hydrochloride in order to improve its compatibility.The modified h-BN with montmorillonite was used to synthetize h-BN-PVA-composites with high thermal conductivity and the thermal conductivity finally reached 17.4 W·m-1·K-1.(3)Ferric chloride-graphite-intercalation-compounds(FeCl3-GIC)was synth-etized and we studied its thermal conductivity.Different graphite-intercalation-compounds(GIC)were synthetized by intercalation of different moleculars and ions,and GIC has excellent physical and chemical properties.In this study,FeCl3-GIC with different structure were synthetized by different mass ratio of materials and reaction time.FeCl3-GIC has higher thermal conductivity than graphite which was ascribed to its unique layer spacing created by intercalation reaction.Finally,thermally conductive FeCl3-GIC was synthetized,and we proved the relationship between structures and thermal conductivity of FeCl3-GIC,the thermal conductivity reached 42.9W·m-1·K-1.