Preparation And Thermal Conductivity Of Silicion Rubber/boron Nanocomposites

Silicone rubber has excellent properties of high and low temperature resistance,weather resistance,shock and wear resistance,corona resistance,electrical insulation,chemical inertness and biocompatibility,etc.It is widely used in elastic bonding,heat dissipation,sealing and other fields in aerospace,electronic and electrical,automotive machinery,medical and health care.However,the thermal conductivity of silicone rubber is poor.Therefore,there are many researches and applications on the preparation of filled thermal conductive silicone rubber by filling thermal conductive filler in the silicone rubber matrix.And it is of great significance to find a suitable thermal conductive filler and study the relationship between the structure and performance of composite materials.In this paper,high temperature vulcanized mixed silicone rubber is used as the matrix,and the mechanical blending method of the mixing machine is adopted to disperse the heat conducting filler into the matrix.Through the observation of the composites'microstructure,and the tests of its thermal conductivity,mechanical properties,hardness,density,hydrophobic properties and other properties,the effects of Al2O3,SiC and BN with the same particle size on the thermal conductivity of silicone rubber composites were studied.And the influence of the filling amount of Al₂O₃ and BN on the thermal conductivity and density of silicone rubber composites was studied and analyzed.In view of the influence of thermal conductivity filler on thermal conductivity of silicone rubber composites,the Maxwell-Eucken model and its modified model,EMA model,Bruggeman model and Y.Agari model were used for theoretical simulation and analysis.The eresults showed that when it was filled with 30phr inorganic filler,the boron nitride had the most significant effect on the thermal conductivity of the silicone rubber composites and the density of the composites was relatively small.This is because,at the same filling amount,the higher the thermal conductivity of the inorganic thermal conductivity filler is,the higher the thermal conductivity of the silicone rubber composite is.Moreover,the thermal conductivity of silicone rubber composites filled with 20-30phr BN is equivalent to that of silicone rubber composites filled with 200phr Al₂O₃,and the density of the latter is much higher than that of the former.In order to improve the dispersion of BN in the silicone rubber matrix,SiO₂ was hydrolyzed by Ethyl orthosilicate?TEOS?in sol-gel method and then coated on the surface of BN to produce modified filler BN@SiO₂.Composite materials were prepared by adding BN@SiO2 to the silicone rubber matrix to study its thermal conductivity and other properties.Results show that TEOS hydrolysis by sol-gel generate SiO2 and coated on the surface of BN,at the same time makes the van der waals force between BN particles or BN and silicone rubber molecular chain stronger.Low filling is beneficial to improve the dispersion of fillers in silicone rubber matrix.When the ratio of BN to TEOS is 2:1 and the filling amount of2BN@SiO2 is 30phr,the thermal and mechanical properties of silicone rubber composites are the best,relatively.In addition,the thermal stability and hydrophobicity of silicone rubber composites were improved by adding modified filler.As the preparation of modified filler BN@SiO₂ requires strict control of reaction conditions,its application in industry is limited.Therefore,Make 500nm,100nm,50nm of BN respectively mixed with 1?m BN,and the effects of the size of smaller particles and the compounding ratio of the two kinds of filler particle size on the thermal conductivity of silicone rubber composites were studied.The results showed that the thermal conductivity of the composite was 1.496w/?m·K?when filled with 20phr 1?m BN and 40phr smaller particle size BN at 100nm,which was 2.07 times of that of the silicone rubber composite filled with60 pieces of 1?m BN,and had a more significant effect on the thermal conductivity of the silicone rubber composite than the one filled with 500nm or 50nm.When 1?m BN is mixed with 50nm BN,the mass ratio of the bigger particle size to smaller one is 30:30?or 1:1?,the thermal conductivity of the silicone rubber composite material reaches 2.632W/?m·K?,which is 3.65 times of the thermal conductivity of the silicone rubber composite material filled with60 pieces of 1?m BN,and had a more significant effect on the thermal conductivity of the silicone rubber composite than the mass ratio of the bigger particle size to smaller one in20:40 or 40:20?1:2 or 2:1?.This is because,when 1?m BN is compounded with 500nm BN,the smaller diameter BN fills the void or surrounding of the larger diameter BN,increasing the probability of contact between the fillers,but there are still large gaps.When 1?m BN compounded with 100nm BN,since the particle size 100nm BN is smaller,so there would be more 100nm BN particles filled in the matrix than the 500nm BN of the same quality,and the clearance between the particles became smaller,and the silicone rubber matrix between particles is thinner,so that the thermal resistance of the composite is smaller,which is beneficial to form a good network of thermal conductivity,and play a synergistic effect of distribution of different particle sizes effectively.