Preparation Of Boron Nitride/Expanded Graphite Heterostructures And Properties Of Epoxy Resin Composite

With the advent of the 5G era,the development of electronic and optoelectronic devices has accelerated.Electronic devices gradually tend to be highly integrated.The device which more power consumed leads to the safety and durability of the device being threatened.A large number of electromagnetic wave radiation interferes with the normal operation of electrical appliances and endangers human health.These problems will have an impact on the service life of equipment and people’s production life.The preparation of high heat dissipation and high electromagnetic shielding performance of electronic packaging materials has become a necessary path for the further development of electronic and optoelectronic devices.Polymers are increasingly used in new energy vehicles,medical devices and portable electronic devices.However,their lower thermal conductivity and lower electromagnetic shielding effectiveness are extremely detrimental to the normal operation of the devices.Therefore,it is common to prepare composite materials by adding fillers to improve their thermal conductivity and electromagnetic shielding performance.The following problems exist in the preparation of thermally conductive electromagnetic shielding polymer matrix composites at home and abroad:(1)Simple blending of fillers is the most direct way to prepare isotropic thermally conductive electromagnetic shielding materials.However,to achieve satisfactory results,it is inevitable to fill a large amount of fillers.This will lead to a sudden increase in the viscosity of the composite material and difficulty in dispersion.And it causes a decrease in mechanical properties.The advantages of fillers can be effectively utilized by the design of specific structures,and more efficient pathways can be constructed with a small amount of fillers.However,the interfacial thermal resistance between the fillers leads to a less significant increase in thermal conductivity,especially through-plane thermal conductivity.(2)The electromagnetic shielding function is often achieved thanks to the construction of conductive networks.How to design the structure so that the composite retains the electromagnetic shielding properties while retaining the electrical insulation is an urgent problem.In view of the above problems,expanded graphite(EG)and boron nitride nanotubes(BNNTs)are selected as fillers,and the design of thermal pathways and the construction of electromagnetic shielding networks are focused to improve the comprehensive performance of the composites.Finally,epoxy resin(EP)is fully infiltrated into the filler skeleton by vacuum-assisted impregnation method to obtain a series of epoxy composites with fine filler structure.The microstructure and chemical composition of the fillers,electrical properties,electromagnetic shielding properties,and thermal conductivity are systematically investigated.The pre-configured threedimensional thermal conductivity network provides a fast channel for phonon transport,and the composites have good overall performance and exhibit excellent thermal management and electromagnetic shielding capabilities.First,the worm-like EG is prepared by high-temperature expansion method.The graphite blocks are cold pressed by the molding method into an orderly arrangement in the horizontal direction.The graphite flakes at the micron level lap each other,constituting a rearrangement of ordered clusters of worms in space.Based on this structure,the prepared EG frameworks are filled with epoxy resin under vacuum assistance and cured at high temperature to obtain composites with different loadings.The combination of the horizontal orientation of the graphite flakes and the transverse Van der Waals(vdW)at the micron level resulted in the expanded graphite/epoxy(EG/EP)composites with an in-plane thermal conductivity of 29.23 Wm-1K-1.It also has the highest electromagnetic shielding effectiveness of 33.07 dB in X-band at the same loading(50 wt%).Secondly,a hybrid filler similar to caterpillars is fabricated by growing BNNTs in situ between EG layers based on chemical vapor deposition(CVD)technique.Similarly,the filler is molded.And the resulting framework is vacuum infused with epoxy resin to obtain expanded graphite/boron nitride nanotube hybrid structure/epoxy resin(EBNT/EP)composites.The through-plane thermal conductivity of the epoxy-based composites can reach which reduces the interfacial thermal resistance.In addition,due to the presence of this three-dimensional structure,the composites have an electromagnetic interference(EMI)shielding performance of 33.34 dB while maintaining electrical insulation.In this work,the expanded graphite layered structure is constructed by compression induced lap splicing of large size graphite flakes.The epoxy resin matrix composite has high in-plane thermal conductivity and EMI shielding performance.To further improve the through-plane thermal conductivity as well as to achieve electrical insulation,insulating high thermal conductivity BNNTs are grown between the EG layers.The three-dimensional network structure is prepared.The epoxy resin-based composites are made to have high in-plane and through-plane thermal conductivity and electromagnetic shielding properties as well as excellent electrical insulation properties.This study provides a new idea for the structural design and preparation process optimization of thermally and electromagnetically shielding bifunctional polymer matrix composites.