| The rapid development of electronic and telecommunication equipment,on the one hand,brings us a lot of convenience,on the other hand,the development of high frequency,high integration and miniaturization of electronic equipment will also bring a lot of problems.Electronic equipment will inevitably produce electromagnetic wave in the process of operation,and with the higher and higher frequency of equipment operation,operation speed is faster and faster,the electromagnetic wave harm generated will be more and more intense;With equipment running at high frequencies,the heat generated by highly integrated,miniaturized electronic equipment is difficult to extract.With equipment running at high frequencies,the heat generated by highly integrated,miniaturized electronic equipment is difficult to extract.Heat accumulation may affect the normal operation of the device,or even cause damage to the device.Therefore,the development of multifunctional materials with high thermal conductivity and high electromagnetic shielding has become an important research direction at present.In this paper,CNT/CNF composites were prepared by using carboxy-modified multi-walled carbon nanotubes(CNT)as fillers and cellulose nanofibers(CNF)as substrates by simple mixing,volatilizing and scraping methods.With the increase of CNT filling amount,the conductivity and electromagnetic shielding performance of CNT/CNF composite films increase gradually.When CNT filling amount is 50wt%,the shielding performance of the composite film in X-band>30dB,and the shielding mechanism is mainly absorption shielding.When the filling amount of carbon nanotubes is 40wt%,the shielding efficiency,thickness and density reach the best balance.Its specific shielding performance per unit thickness(SSE/t)reaches 6758.72 dB·cm2/g.Compared with the previously reported CNT shielding material,the CNT/CNF composite film prepared in this paper can not only have high electromagnetic shielding performance,but also maintain sufficient thinness.The inplane thermal conductivity and through-plane thermal conductivity of the composite film reach the maximum when the CNT filling amount is 20wt%.The in-plane thermal conductivity was 8.69 W/(m·K),which increased by 558%.The through-plane thermal conductivity is 1.04 W/(m·K),which is increased by 369%.The addition of CNT is helpful to improve the mechanical properties of composite films,and the maximum tensile strength of CNT/CNF composite film is 72.49MPa when CNT filling amount is 20wt%.In practical application,the high conductivity of materials is not a good performance,which will limit its application field to a certain extent.this paper introduces BN/CNF composite film with high insulation and thermal conductivity,and makes use of laminated hot pressing technology to prepare surface insulating composite material with high thermal conductivity and high electromagnetic shielding.BN exhibits good horizontal orientation in CNF matrix due to the influence of shear force and gravity.BN is in contact with each other to build a heat conduction path;There was no obvious stratification between different layers of the laminated film.The laminated composite film has good flexibility,no matter it is bent or fully folded composite film will not fracture,and the surface of the composite film after bending and folding will not leave obvious creases.BN/CNF has almost no EMI shielding performance,and its lamination with CNT/CNF composite film has little effect on the shielding performance of CNT/CNF composite film.The electromagnetic interference shielding performance of the film can be improved effectively by multilayer composite lamination design.The horizontal and vertical thermal conductivity of 40(2+1)laminated film is higher than that of 40CNT,but slightly lower than that of 30BN.It is proved that 2+1 lamination can retain the good thermal conductivity of the monolayer film involved in lamination.The surface conductivity of the laminated film is in the order of 10-10,indicating that the film has good insulation performance. |
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