Preparation And Properties Of New Boron Nitride/silicon Rubber Thermally Conductive Composites

Thermal conductive silicone rubber can effectively reduce thermal resistance,transfer heat,promote heat dissipation,which have a wide range of applications in these fields of the electronics,electrical appliances,telecommunications,power and so on.The development of society and science technology has put forward new and higher requirements for thermal conductive silicone rubber.Thermal conductive fillers have a decisive influence on the properties of thermal conductive silicone rubber.Hexagonal boron nitride(h-BN)is an ideal thermal conductive filler with highly thermal conductivity and superior insulation performance.However,due to poor dispersion and serious viscosity increase problems,it is difficult to apply hexagonal boron nitride/polymer-based thermal conductive composite materials.In order to overcome these problems,this paper developed the hypergravity deposition method,and the main research contents are as follows:Hexagonal boron nitride/silicone rubber(h-BN/SR)composites were prepared by hypergravity deposition method.Rheological tests showed that the h-BN/SR mixtures had a significant viscosity increase.The high viscosity of the mixtures causes obvious obstacles to the mixing and forming process.The results of electron microscopy showed that h-BN formed uniform dispersion in the silicone rubber matrix,but the h-BN particles overlapped with each other and formed holes,resulting in the non-compact microstructure of the composites.The thermal conductivity of h-BN/SR thermal conductive composites without hypergravity treatment is 1-1.6 W/m K(initial concentration 20-35%),while the thermal conductivity of h-BN/SR thermal conductive composites with hypergravity treatment can reach 3.14 W/m K(initial concentration 30%,centrifugal speed 15000 rpm,time 0.5 h).In order to solve the problem of non-dense microstructure of h-BN/SR thermal conductive composite materials,spherical boron nitride/silicone rubber(sBN/SR)thermal conductive composites were prepared through hypergravity deposition method.The rheological tests showed that the sudden increase of viscosity caused by spherical boron nitride was weaker than that caused by hexagonal boron nitride.The results of electron microscopy showed that the spherical boron nitride formed uniform dispersion in the silicone rubber matrix,and the composites had a highly compact microstructure.The thermal conductivity of sBN/SR thermal conductive composites treated by hypergravity can reach 4.0 W/m K(initial concentration 40%,centrifugal speed 15000 rpm,time 0.5 h),which is significantly higher than that of h-BN/SR or sBN/SR thermal conductive composites without hypergravity treatment,and also higher than that of h-BN/SR thermal conductive composites treated by hypergravity treatment.Thermal management research showed that the sBN/SR thermal conductive composites can reduce the surface working temperature of LED by an additional 5℃.In this paper,invented hypergravity deposition method,which prepared a series of boron nitride/silicone rubber thermal conductive composites and better solve the poor dispersibility and sudden viscosity increase problems of boron nitride,make composites forming dense microstructure,effectively improve the thermal conductive performance of the composites,which can provide the reference for similar problems of dispersion and increase viscosity in these fields of carbon material/polymer composites,two-dimensional material/polymers,polymeric thermal conductive composites,and so on.