| In recent years,electronic equipment has rapidly changed to miniaturization and high integration,and with it is the rapid increase in power density.If the heat cannot be dissipated in time,the accumulated heat will greatly reduce the service life and reliability of electronic devices.Silicone rubber(SR)has the characteristics of high elasticity,electrical insulation,and strong chemical stability and is widely used in thermal interface materials,but its intrinsic thermal conductivity is low,which limits the application prospects of silicone rubber.Filling the thermally conductive filler is a common approach to improve silicone rubber composites thermal conductivity.However,traditional fillers have requirements for the filling amount,and the thermal conductivity of the composite material will be significantly improved just under high filling.The addition of a large number of incompatible fillers will cause problems such as deterioration of the mechanical properties of silicone rubber and difficulty in processing and molding.At present,the thermal conductivity of filled composites is mainly improved from the two major directions of filler surface functionalization and design of filler network structure.This article is mainly divided into three aspects for research:1.The use of combination of dopamine modified fillers and silane coupling agents.Hexagonal boron nitride(h-BN)has the characteristics of high thermal conductivity,high mechanical properties,and electrical insulation,so h-BN is selected as the thermally conductive filler.However,h-BN lacks active groups due to its surface inertness,so the traditional modification efficiency is low.In this paper,a modification method of dopamine-coated boron nitride grafted KH550 is proposed,and the effect of filler content and modification conditions on the properties of silicone rubber composites is studied.XRD,SEM,XPS and other characterization methods were used to prove the modification results,and the BN-PDA-KH550/SR composite material was prepared by the vulcanization molding process.A 12 nm film is deposited on the surface of the modified boron nitride.At the same time,the introduction of active groups will make it stronger with the matrix.Therefore,the thermal conductivity and mechanical properties of the BN-PDA-KH550/SR composite material are better than those of the h-BN/SR composite material.The highest thermal conductivity at 30vol%content is 1.61 W/(m·K),which is 8.05 times that of pure silicone rubber.2.Adopting the design idea of the segregated network,adding silicon rubber particles to build a heat conduction path.Firstly,the micron-sized silicone rubber particles(SRP)are prepared by the dynamic vulcanization method,and then the modified filler prepared in the previous section is blended with the unvulcanized rubber,and then blended with the silicone rubber particles after uniform mixing.During the mixing process,the filler cannot be filled into the Pre-vulcanized SRP,and the uncrosslinked SR will act as a binder during the hot pressing process,and the BN-PDA-KH550@SRP/SR composite will be obtained after the vulcanization process Changing the ratio of pre-vulcanized particles and uncrosslinked SR,the blending matrix with a suitable ratio will present a continuous path,and the filler will be selectively distributed in the rubber phase between the pre-vulcanized particles,which increases the effective concentration of the thermally conductive filler and establishes continuous filler network,which has a significant effect on improving the thermal conductivity of silicone rubber composites.Scanning electron microscopy results show that the filler is present in the SR around the particles,which is conducive to phonon transmission.Therefore,the thermal conductivity of 30 vol%BN-PDA-KH550@SRP/SR composite material is greatly improved,and the thermal conductivity reaches 2.24 W/(m·K).In addition,hardness and tensile tests show that the addition of fillers does not significantly reduce the mechanical properties of the composite material.Compared to the pure SR,BN-PDA-KH550@SRP/SR composites also exhibit good heat capacity,high thermal stability,dielectric constant and dielectric loss is also low level.3.Using TG-DTG thermal analysis technique explored at different heating rates(β=5,10,15,20℃/min)BN-PDA-KH550@SRP/SR composites thermal decomposition kinetics movable.The results show that the filling amount has a significant effect on the thermal decomposition process of the silicone rubber composite material.The larger the filling amount,the greater the stability of the composite material;Calculated by Kissinger method,the thermal decomposition activation energy Ea of silicone rubber is 78.05 KJ/mol,and the Ea of 15 vol%silicone rubber composite is 113.26 KJ/mol;The Flynn-Wall-Ozawa method is used to calculate the activation energy at different stages.As the conversion rate increases,the activation energy increases in the initial stage,remains stable in the middle stage,and rises sharply in the later stage;The results indicate that the construction of thermal conductive network may induce the to formation of a char residue barrier on the surface of TC network,which hinders the further heat transfer to the interior of rubber particles and makes the decomposition of rubber particles occur at higher temperature;The Coast-Redfern method was used to verify the reaction order.The reaction order of the silicon rubber composite in the pyrolysis process is one,indicating that the heating rate does not affect the thermal decomposition reaction type of the silicone rubber composite. |
PDF Full Text Request