Preparation And Structural Properties Of Borbon Nitride/epoxy Based Thermal Conductive Composites

As a thermal conductive packaging material,polymer resin has been widely used in microelectronics industry,aerospace,electrical machinery and other high-tech fields.The process of improving the thermal conductivity of the intrinsic thermal conducting polymer is very complicated,and the synthesis process is complicated,and the synthesis cost is high.Filled thermal conductive polymer matrix composites have the advantages of high thermal conductivity,various processing methods and low cost.Epoxy resin,with its good chemical resistance(acid,alkali,salt),electrical insulation,high adhesion and good mechanical properties,stands out among a number of high molecular polymer,and becomes an excellent choice for filling thermal conductive composite materials.As a thermal conductive inorganic filler,boron nitride has the characteristics of high temperature stability,high thermal conductivity,low friction coefficient,high strength,high resistivity,corrosion resistance and so on,which become the research object of this paper.In this paper,the boron nitride filler was firstly stripped by the mechanical force with the ammonia,and then the three particle sizes was modified by the silane coupling agent KH560.Transmission electron microscopy,nano-particle size analysis,XRD and other methods were used to analyze the peeling effect.The results showed that the particle size of 5?m boron nitride after exfoliation was mostly distributed within the range of 290?1300nm,while the particle size of 0.5?m boron nitride after exfoliation was mostly distributed within the range of100?300nm.The lamellar layer is stripped from the previous multiple layers to 5?10 layers.XPS,TGA,infrared and other test results showed that the boron nitride with three particle sizes was successfully connected to the oxygen-containing functional groups such as Si-(CH₂)₃ and Si-O-CH₃ after modification.The content of C and O elements increases,and the percentage of thermogravimetric content increased.First the modified boron nitride and ammonium bicarbonate were mixed and pressed at room temperature.Then the mixture is heated at 80?to form 3D-BNNS(3D Boron nitride nanosheet)foam.Finally,the foam loaded with different 3D-BNNS content was infiltrated by epoxy resin and then cured to obtain 3D-BNNS/epoxy composite material.It was found that the glass transition temperature of the composite increases as the increasement of 3D-BNNS content loading,and the heat resistance and thermal stability of the composite are effectively improved compared with the pure epoxy resin.When the content of 3D-BNNS foam is 20 wt%,thermal conductivity coefficient of the composite is 1.193 W/(m?K),improving 569%compared to pure epoxy resin.Under inspection of composite's microstructure,3D network structure for heat conduction is observed while there are also some defects in the form of pore.In addition,the dielectric constant and dielectric loss factor corresponding to 1m Hz of 3D-BNNS/epoxy composites with a content of 20wt%are 5.68 and 0.009 respectively.The resistivity and conductivity tests show that the3D-BNNS/EP composite has excellent insulation performance,and the volume resistivity is 10¹⁵.To solve the problem of porous defects in the subsequent preparation of thermal conducting composites which is caused by the 3D thermal conducting network formed by the mixture of boron nitride and ammonium bicarbonate,this paper further explores another method for the constructing thermal conduction network.Polyethersulfone(PES)is first mixed with epoxy resin(EP)and then BNNS is added.During the curing process of epoxy,reaction induced phase separation(RIPS)occured and forming bi-continuous phase structure of PES and EP.BNNS which distributes at the bi-continuous interface of PES/EP forming thermal conduction network.The results showed that the addition of PES promoted the curing of epoxy resin,and BNNS successfully distribute along the interface between PES and EP which forming a heat conduction network.When BNNS content is 15 wt%,the thermal conductivity of BNNS/PES/EP composite is 0.54 W?m^-1?K^-1,increasing 269%compared with the pure epoxy resin.Compared with previous3D-BNNS thermal conduction network in the form of foam,the thermal conducting composite with bi-continuous phase through RIPS has fewer internal defects.As the content of BNNS is15wt%,flexual strength of BNNS/PES/EP thermal conducting composite on average is 84.97 MPa,the tensile strength is 33.08 MPa,the impact strength is 38.8 J/m.Compareed with the BNNS/EP composites,the flexural strength,tensile strength and impact strength of BNNS/PES/EP composites are increased by 69.97%,100.24%and 20.50%respectively.