Application of fumed silica in silicone rubber
Gas-phase silica is one of the most important high-tech ultra-fine inorganic materials. Because of its small particle size, it has large specific surface area, strong surface adsorption, large surface energy, high chemical purity, good dispersibility, thermal resistance, resistance and other special properties. It has unique characteristics in many disciplines and fields because of its superior stability, reinforcement, thickening and thixotropy. It plays an irreplaceable role. Today Xiaobian and everyone to learn about the application of gas-phase silicon dioxide in silicone rubber.
Application of fumed silica in HTV silicone rubber
The use of fumed silica can be divided into organosilicon materials and other fields. Among them, the amount of fumed silica in organosilicon materials accounts for nearly 60% of the total amount of fumed silica. Silicone rubber is the most widely used material in organosilicon materials, and its addition amount can be as high as 50%. Vapor-phase silicon dioxide plays a major reinforcing role in HVT silicone rubber. Because the molecular chain of silicone rubber is very flexible and the interaction between chains is weak, the strength of unreinforced silicone rubber is very low (no more than 0.4 MPa) and has no use value. It must be reinforced before it can be applied. The strength of silicone rubber reinforced by vapor-phase silicon dioxide can be increased by 40 times.
Effect of fumed silica on mechanical properties of HTV silicone rubber
The reinforcing effect of fumed silica on HTV silicone rubber is affected by its particle size, comparative area and structure. Generally, the smaller the particle size, the higher the specific surface area, the higher the structure, the better the reinforcing effect, and the higher the strength and hardness of the vulcanizate. In addition, the amount of fumed silica and its dispersion in the matrix also have a great impact on the properties of vulcanizates. Fig. 1 shows the effect of the amount of fumed silica on the tensile strength of vulcanizates. As can be seen from the figure, the strength of vulcanizate increases with the increase of the amount of fumed silica, which usually reaches the peak value at 35-50 phr. There are many reinforcing mechanisms and models of fumed silica for silicone rubber. The more accepted explanation is that the free hydroxyl groups on the surface of fumed silica form physical or chemical bonds with silicone rubber molecules, and a silicone rubber molecular adsorption layer is formed on the surface of silica, forming a three-dimensional network structure of fumed silica and silicone rubber molecules, thus effectively restricting silicone rubber. Molecular chain deformation and reinforcement. The tear strength of vulcanizates is similar to the tensile strength. It increases with the increase of the reinforcing ability of fumed silica, increases first with the increase of the amount of fumed silica, reaches the peak value and then decreases slightly.
EFFECT OF GAS SILICON DIOXIDE ON PROCESSING PROPERTIES OF HTV SILICON RUBBER
The influence of fumed silica on the processability of HTV silicone rubber is generally expressed by the degree of structuralization (Crepe). _Crepe is equal to the difference between the plasticity value (p28) of the blends stored at room temperature for 28 days and the plasticity value (P 0) determined immediately after mixing. The plasticity value of the rubber is related to the amount, surface properties and structure of fumed silica. The reason for the structure is that the hydrogen bond between the surface hydroxyl group of fumed silica and oxygen atom in silicone rubber and the molecular chain of silicone rubber adsorbed on the surface of silica lead to the decrease of the fluidity and hardening of the rubber with the prolongation of time, which affect the processing performance. Therefore, it is necessary to add structural controllers or choose the surface-treated gas-phase silica, structural controllers and surface treatment of gas-phase silica in the course of use. All of these are through the reaction of structural controllers or surface treatment agents with silicon hydroxyl groups on the surface of silica, thus reducing the number of surface hydroxyl groups, reducing the number of hydrogen bonds formed with silicone rubber and mixing them. The mixing time of the rubber is shortened and the plasticity is increased, which can reduce the structural effect and improve the processing performance and storage stability.
Application of Gaseous Silica in Room Temperature Vulcanized (RTV) Silicone Rubber
Room temperature vulcanization (RTV) silicone rubber can be divided into two categories: single component (RTV-1) and two component (RTV-2) in product morphology, and condensation and addition systems in vulcanization mechanism. All kinds of room temperature vulcanized silicone rubber need filler reinforcement to be useful. At present, fumed silica is the most effective filler for RTV silicone rubber reinforcement. Because RTV silicone rubber is generally used as sealing material for pouring, seaming and coating, in order to maintain the viscosity and fluidity before vulcanization, the amount of gas phase silicon dioxide is generally much less than that of high temperature vulcanized silicone rubber, and it is often used with other reinforcing and semi-reinforcing fillers in order to facilitate construction operation.
EFFECT OF VAPOR SILICON DIOXIDE ADDITION ON TENSILE STRENGTH AND HARDNESS OF RTV SILICON RUBBER
Gas-phase silicon dioxide is a very effective reinforcing filler for RTV silicone rubber, which can significantly improve its strength. This is due to the small size effect and large specific surface area of gaseous silica particles. On the other hand, the surface of gaseous silica particles contains many silicon hydroxyl groups, which can form network structure through hydrogen bonding and van der Waals force. At the same time, silica particles interact strongly with polysiloxane molecules and improve the interfacial bonding. The smaller the particle size of fumed silica, the larger the specific surface area, the larger the contact surface between particles and rubber, and the more the bonding points, the better the reinforcing performance of RTV silicone rubber, the higher the tensile strength, tear strength, wear resistance and hardness of vulcanizate, but at the same time, the dispersion becomes very difficult, the elasticity decreases, and the processing performance deteriorates. Therefore, RTV silicone rubber is generally chosen with a relatively low specific surface area (200m2/g). Gas dioxide