Macro-scale Preparation Of Boron Nitride Nanosheets And Its Application In Thermally Conductive Composites

Nowadays,with the rapid development of science and technology,the methods of social production and daily life that are closely related to us have been greatly changed.Among them,thermally conductive polymer materials are an indispensable part,but most of the polymer materials are generally low thermal conductors,that is,low thermal conductivity and the thermal conductivity is usually less than 0.2 Wm^-1K^-1,Such low thermal conductivity restricts its use in some specific fields.Generally speaking,the addition of thermally conductive fillers to the polymer matrix is an important method to solve this problem.Moreover,how to choose the right thermally conductive fillers also affects the performance of the matrix materials.Hexagonal boron nitride nanosheets(BNNSs)not only have graphene-like properties,but also have stable physicochemical properties and low dielectric constant,which makes it a good substitute for graphene materials in certain fields.In this paper,we first studied the large-scale preparation method of BNNSs,then added the fillers to thermally conductive polymers to prepare polymer composites,analyzed the properties and structure of BNNSs obtained by high-pressure liquid phase exfoliation,and studied polymer compounding Material thermal conductivity and insulation properties.The thesis mainly starts from the following two aspects:1)The hexagonal boron nitride(h-BN) was exfoliated by a simple,efficient and environmentally friendly high-pressure liquid phase method.The study mainly analyzed the exfoliation frequency and the effect of exfoliation pressure on h-BN exfoliation.By characterizing and observing the structure and micro-morphology of hexagonal boron nitride nanosheets exfoliated by high-pressure liquid phase,the results show that when the pressure is100 MPa,the size of the BNNSs is uniform and the specific surface area is moderate after exfoliation.And after 100 cycles exfoliation,the lateral dimensions and thickness of the BNNSs are significantly reduced,and the thickness is about 57.8 nm.At the same time,the lattice structure of the boron nitride nanosheets obtained by this method will not change after the exfoliation process.The process also does not introduce new impurities.The yield of hexagonal boron nitride stripped by high-pressure liquid phase method can be as high as 42.3%after 100cycles exfoliation,which can realize large-scale preparation of BNNSs.2)The BNNSs prepared by high-pressure liquid phase are mixed with polydimethylsiloxane(PDMS)to prepare BNNSs/PDMS composites,which containing different fillers.At the same time,in order to study the thermal conductivity of composites with different shapes,spherical boron nitride(S-BN)/PDMS composites containing the same amount of filler were prepared.The results show that the BNNSs/PDMS composite exhibits better thermal conductivity.When the filler content is 35 wt%,the thermal conductivity of the BNNSs/PDMS can reach to 1.16 Wm^-1K^-1.This is mainly because the BNNSs connect with each other and more likely to form thermal paths in the polymer matrix,which effectively reduces the phonon scattering at the interface between the thermally conductive fillers and the polymer.It is more worth mentioning that with the addition of thermally conductive fillers,not only the volume resistance and breakdown strength of the composite material have been improved to a certain extent,but also the fire resistance properties of the material have been guaranteed.Therefore,in summary,adding BNNSs to the polymer matrix can effectively improve the lack of matrix performance,Therefore,the polymer materials are more fully applied in the thermal field.