Preparation And Studies On Thermally Conductive Silicone Rubber

With the development of industry and science, the demand of thermal conductivity materials expands fastly. Silicone rubber has been widely applied in many field due to the outstanding properties, such as high and low temperature durability, old resistance properties, electric insulator and so on. Therefore, more attention has been paid to the research of thermal conductivity silicone rubber. Accordingly in this article, we report the preparation of thermal conductivity silicone rubber filled with metal powders, metal oxide and graphite, and the factors which influence the properties of silicone rubber. However, the use of silicone rubber is limited because of the poor mechanical properties. So the enhancement of the mechanical properties is very important, and the mechanical properties are studied by blending diverse vinyl content silicone gums.The silicone rubber was prepared by using metal powders, graphite, metal oxide and nitride as fillers. Although the thermal conductivity coefficient of metal powders were high, they were hard to disperse. Meanwhile their density were also high, so the thermal conductivity paths could be formed only when the filler content was high. Also, the high density of metal powders made the density of the rubber high. The mechanical properties of the composites decreased because of the poor interaction between the rubber and the metal powders. The thermal conductivity coefficient of the silicone rubbers was good when graphite was used as fillers because of the layered structure. Meanwhile, the decrease of the mechanical properties was low, however, the filler content was less than spherical fillers. Although the metal oxide and nitride had lower thermal conductivity coefficient than metal and graphite, they were easy to fill the rubbers and they can also reinforce the rubbers. So, the rubber can achieve high thermal conductivity coefficient when the filler content was large, and the mechanical properties were good.The shape of the fillers has an important influence on the formation of the thermal conductive paths. It was easy to form thermal conductive paths for fillers whose shape were flakelike such as graphite. And the composite would achieve high thermal conductivity coefficient when the filler content was low. However, the filler content was limited because of the special shape. Although the spheric fillers had little influence on the thermal conductivity coefficient when their content is low because of their low thermal conductive coefficient, they can pack easily, so that the filler content can be very large. Especially, the composite can get high thermal conductive coefficient when fillers of different size blended.The thermal conductivity coefficient would decrease when the composite was cured. This was because the continuous phase of the composite changed. The thermal conductivity coefficient would increase with the increment of the crossliking density after the rubber was cured, however, the influence was limited. The thermal conductivity coefficient would be enhanced when the concentration crosslinking agent was used for gums of low molecular wight.The interaction between silicone rubber and fillers had an important influence on thermal conductivity. The stronger the interaction was, the higher the thermal conductivity showed. The treatment of the filler surface played an important role in thermal conductivity and mechanical properties and the results revealed that the rubber prepared with the fillers treated with coupling agent in alcohol showed higher thermal conductivity coefficient.The additive, such as plasticiser and surface active agent, will show impact on the thermal conductivity and the mechanical properties in the processing of rubber. Dimethyl phthalate was added into the silicone rubber, and the elongation and tearing strength were improved. The hardness of the rubber was lowered. While the addition of surface active agent led to the enhancement of the thermal conductivity coefficient and elongation and the decreasement of the tensile strength.The polymer will migrate to the surface of the rubber, and then will form a polymer film, which will lower the thermal conductivity of the composite. As a result, it is effective of treating the rubber surface for improving the thermal conductivity coefficient. That is, the silicone rubber was polished to move the polymer surface of the composite away, and then the thermal conductivity could be enhanced. However, the mechanical properties decreased.Silicone rubbers composed of diverse vinyl content silicone gums blending were prepared and their mechanical properties were studied. The results showed that the silicone rubber from gums with diverse vinyl content blending which is concentration crosslinking had higher tensile modulus and higher tearing strength than that with single 0.16% vinyl molar content which is mean crosslinking. Comparing with the single vinyl content silicone gums, the diverse vinyl content gums blending crosslinked more completely because of their more and concentrated vinyls. The DMA demonstrated that all the samples had different Tg and the rubber composed of less vinyl content gums blending with more vinyl content gums had better flexibility at low temperatue. The storage modulus and loss modulus decreased with the increment of temperature. In addition, the 0.04% vinyl content gums blending with the 0.3% vinyl content gums had largest storage modulus.