Preparation And Property Study Of Thermal-conductive Silicone Rubber

Thermal conductive filler (graphite, carbon black and alumina) and crosslingking agent were dispersed in poly(vinylmethyl siloxane) using a two-roll mill, and then cured in a mould under pressure to obtain the thermal-conductive silicone rubber with good mechanical properties. Factors that influenced the thermal conductivity and mechanical properties of silicone rubber were systemically studied. Based on the experimental results, a modified thermal conductive model for polymer-based composites was proposed. In addition, the heat-resistance of thermal-conductive silicone rubber was also investigated.High thermal conductive fillers such as graphite were in favor of preparing highly thermal-conductive silicone rubber with low content. Thermal conductivity and mechanical properties of silicone rubber filled with the mixture of graphite and carbon black were better than those with graphite. When carbon black/graphite mass ratio was 1/5 and the total dosage was 30 weight parts, the hardness, tensile strength, elongation at break, and thermal conductivity coefficent of silicone rubber prepared were 74 shore A, 7.67 MPa, 498.7%, and 0.644 W·m^-1·K^-1, respectively.Agari equation agreed quite satisfactorily with the thermal conductivity coefficents of silicone rubber filled with allumina, however, there was deviation between the data predicted by Agari equation and the experimental data of silicone rubber filled with graphite. A new theoretical model that described thermal conductivity of polymer composites has been established based on the thermal conductive mechanism. The model could successfully illustrate the thermal conductivity of silicone rubber filled with graphite when the volume content of graphite was over 5%.The effect of crosslingking agent, thermal conductive filler, and "concentrative crosslinking" agent on the crosslinking of silicone rubber was studied. The crosslinking density of silicone rubber increased with the increase of the amount of crosslinking agent, while the tensile strength of silicone rubber firstly increased and then decreased with the increase of the amount of crosslinking agent. The addition ofthermal conductive filler resulted in the increase of the physical crosslinking density of silicone rubber, and decrease of the chemical crosslinking density and mechanical properties of silicone rubber. The "concentrative crosslinking" agent significantly improved the mechanical properties of silicone rubber. When 20% D₄^vi was added, tear strength, tensile strength, and elongation at break of thermal-conductive silicone rubber increased by 48.2%, 9.8%, and 19.3%, respectively.Thermal stability of thermal-conductive silicone rubber was investigated by thermogravimetric analysis. The thermal degradation of thermal-conductive silicone rubber filled with graphite began at about 450℃ and the temperature at the maximum degradation rate was about 510℃, which were 20℃ higher than those of the unfilled silicone rubber. The kinetic parameters of thermal degradation of silicone rubber were evaluated by Chang and Freeman-Carroll equations. It was found that reaction order of thermal degradation was between 1.0 and 1.5, and the value decreased with the increase of temperature. The activation energy of thermal degradation for unfilled silicone rubber was 81.5 kJ/mol in the range of 391.5-420.6 ℃, while the activation energy for silicone rubber filled with graphite, carbon black/graphite mixture, and alumina was 99.4, 108.5, and 108.8 kJ/mol at the same temperature range, respectively.