Improving The Flame Retardancy And Thermally Conductivity Of Epoxy Composites By Introducing Hexagonal Boron Nitride

Epoxy（EP）is a polymer material widely used in electronic products,with high electrical insulation,high processability,high adhesion,and good chemical and corrosion resistance,but its thermal conductivity is very poor and very flammable.Microelectronic devices generate serious heat,once the heat accumulation is a serious thermal runaway,it will ignite the epoxy substrate to cause serious loss of life and property.However,the traditional method of directly blending flame retardants and thermally conductive fillers often requires the addition of large amounts of fillers,which is extremely inefficient.The objective of this project is to develop epoxy composites with low filler addition,high thermal conductivity,and good flame retardant properties,and we hope to facilitate their application in high-frequency communication by not affecting the low dielectric constant and low dielectric loss properties of epoxy itself as much as possible.The EP composites with excellent performance were prepared by selecting different flame retardant additions,respectively.The main research content is as follows:（1）The flame retardant was added to the EP prepolymer:a three-dimensional thermal conductivity scaffold was firstly preconstructed by connecting hexagonal boron nitride（h-BN）sheets with Polyethyleneimine（PEI）,and then a phosphate ester hyperbranched flame retardant（DTFR）,which was miscible with the EP prepolymer,was synthesized,allowing the flame retardant to be immersed into the three-dimensional thermal conductivity scaffold along with the EP prepolymer.EP composites were able to increase their thermal conductivity to 1.35 W·m^-1·K^-1 by introducing only12.5 vol%of h-BN,an increase of 744%compared to control EP.In addition,the PHRR and THR of EP composites were significantly reduced by 41.5%and 34.9%,respectively,and the ultimate oxygen index（LOI）was improved by 7.8 compared with control EP.The differences of flame retardant properties in different orientation directions were also investigated.（2）Adding flame retardant to the thermal conductive scaffold:The high molecular weight ammonium polyphosphate（APP）is chosen as the flame retardant,which both exerts its flame retardant effect and effectively helps h-BN to build a three-dimensional thermal conductive scaffold.The innovative combination of flame retardant and thermally conductive filler makes the thermally conductive scaffold with flame retardant effect,simplifying the preparation steps.EP composites were able to increase their thermal conductivity to 1.67 W·m^-1·K^-1 by introducing only 9.1 vol%of h-BN,an increase of 944%compared to control EP.In addition,the PHRR and THR of EP composites were significantly reduced by 54%and 34%,respectively,and the LOI was improved by 5.7 compared to that of the control EP.An in-depth analysis of the high-strength residual carbon generated by combustion was also performed.