Preparation And Properties Of Epoxy-based Thermally Conductive Insulating Composite

With the development of science and technology,the emergence of new applications such as 3D chip structures,flexible electronics,and light-emitting diodes,heat dissipation has become a challenging problem.Due to the advantages of lightweight,corrosion resistance,and ease of processing,polymer composite materials have attracted more attention in applications in electronic packaging and device heat dissipation.In solids,thermally conductive carriers are divided into three types: phonons,electrons,and photons.In the polymer system,since there is no free electrons,the heat conduction mainly depends on the lattice vibration,phonons are the main heat conduction carrier,and the thermal conductivity of the polymer is mainly determined by its own crystallinity and orientation direction.In the case of epoxy resins(EP),the random winding of the internal molecular chain and the inability to move completely freely result in a low degree of regularity.Coupled with the scattering effect of molecular chains on phonons,the thermal conductivity of epoxy resin is very low(0.20-0.88 W/(m·K)).At present,blending polymer matrix with fillers of higher thermal conductivity is an effective way to improve the thermal conductivity of the composite materials.On the other side,hexagonal boron nitride(h-BN,185-300 W/(m·K))is an ideal filler for improving the thermal conductivity of polymers due to its high thermal conductivity and good insulation.In this work,bisphenol A epoxy resin is used as the polymer matrix,h-BN,core-shell structured MWCNTs@Al2O3 and multi-walled carbon nanotubes(MWCNTs)are used as fillers.The different thermally conductive composite material systems are prepared,characterized and discussed.1.Due to the interfacial thermal resistance between h-BN and the epoxy resin matrix,surface treatment of h-BN was performed with ?-aminopropyl triethoxytoluene(KH550).The EP/h-BN-KH550 thermally conductive insulating composite material was prepared by solution blending.The performance of the composite materials obtained after surface treatment were significantly improved.When the h-BN-KH550 content was 40 wt%,the thermal conductivity of the composite material reached 1.18 W/(m·K),which is 5.4 times that of neat epoxy resin.2.In order to reduce the loading of h-BN-KH550,EP/h-BN-KH550/MWCNTs composite materials were prepared.MWCNTs act as a microscopic bridge between the h-BN fillers and the polymer matrix.The introduction of MWCNTs leads to enhancement of the thermal contact,accordingly,h-BN-KH550 forms a primary thermal conduction path in the epoxy resin matrix.The thermal conductivity of EP/h-BN-KH550/MWCNTs composite reaches 0.88 W/(m·K)at 8 wt% MWCNTs and 20 wt% h-BN-KH550 loading,which is 4 times that of pure epoxy resin.Under the premise of greatly reducing the content of h-BN-KH550,the material maintains a high thermal conductivity and good thermal stability.3.Although MWCNTs have excellent thermal conductivity,their high electrical conductivity limits the application of composite materials in the field of thermal insulation.In order to reduce the electrical conductivity of MWCNTs,an Al2O3 insulating layer is introduced on the surface of multi-walled carbon nanotubes with good thermal conductivity,which can not only reduce the amount of filler needed but also improve the thermal conductivity of the material while maintaining the insulating properties of the materials.In this study,the modified sol-gel method was used to prepare core-shell structured MWCNTs@Al2O3.The results show that when the addition amount of MWCNTs@Al2O3 is 6 wt% and h-BN-KH550 is 20 wt%,the thermal conductivity of the composite is 0.72 W/(m·K),which is 3.3 times that of pure epoxy resin;when added The thermal conductivity of the composite material at 2 wt% MWCNTs@Al2O3 and 30 wt% h-BN-KH550 is 0.93 W/(m·K),which is 4.2 times that of pure epoxy resin.The prepared composite material takes into account excellent thermal conductivity,insulation and workability.