Research progress on nano calcium carbonate in RTV silicone rubber applications. Room temperature vulcanizing silicone rubber is now widely used as adhesives, sealants, potting and molding materials, and has applications in various industries. Among them, reinforcing fillers have a very important influence on the rheological and mechanical properties of RTV silicone rubber. Nano calcium carbonate is characterized by its low price, excellent performance, large filling amount, non-toxicity and odorlessness, and can be widely used as a reinforcing filler for RTV silicone rubber.

Research progress on the application of nano calcium carbonate in RTV silicone rubber. Room temperature vulcanizing silicone rubber is now widely used as adhesives, sealants, potting and molding materials, and has its uses in various industries. Among them, reinforcing fillers have a very important influence on the rheological and mechanical properties of RTV silicone rubber. Nano calcium carbonate has the characteristics of low price, excellent performance, large filling amount, non-toxic and tasteless, and can be widely used as a reinforcing filler for RTV silicone rubber.

　　There are two disadvantages of using nano calcium carbonate directly in silicone rubber: firstly, nano calcium carbonate has a large specific surface area, and intermolecular forces, electrostatic interactions, hydrogen bonds, etc., cause the agglomeration of calcium carbonate powder. In addition, nano calcium carbonate is a hydrophilic inorganic compound with poor affinity for organic polysiloxane, easily forming powder aggregates, resulting in uneven dispersion of nano calcium carbonate in the system. Secondly, nano calcium carbonate has a very high oil absorption value, which has a significant thickening effect on the silicone rubber system, and has poor thixotropy, affecting the construction performance of silicone rubber. Therefore, it is necessary to modify the surface of nano calcium carbonate according to the characteristics and requirements of RTV silicone rubber, which can solve the defects of easy flow, poor extrudability, and low strength caused by ordinary nano calcium carbonate.

　　Modification technology of nano calcium carbonate

　　The modification of nano calcium carbonate mainly adopts wet modification, specifically, a dispersant and a surfactant are added to the nano calcium carbonate slurry, and the particle size and surface activation rate of nano calcium carbonate are controlled through the process. Finally, after dehydration, drying, crushing and grading, the modified nano calcium carbonate is obtained.

　　At present, the most used and most effective surfactants are mainly organic compounds of fatty acids. One end of the molecule of this type of compound is a polar group such as a carboxyl group or an ether group, which can physically or chemically adsorb or react with the surface of calcium carbonate particles to form a stable bridging structure; the other end of the molecule is a long-chain alkyl group, which is similar in structure to polymer molecules, and therefore has good compatibility with organic polymers. After surface modification, nano calcium carbonate can significantly enhance the interfacial bonding force between nano calcium carbonate particles and organic polymers, effectively reduce the oil absorption value of nano calcium carbonate, reduce the viscosity of the nano calcium carbonate/organic polymer system, improve the dispersibility and increase the addition amount.

　　Effect of nano calcium carbonate on the rheological properties of RTV silicone rubber

　　In practical applications, not only is high bonding strength and good elasticity required for RTV silicone rubber, but also good construction performance is required to meet the requirements of fine surface or grooves, inclined or vertical surface construction, so the adhesive should not flow, that is, it should have thixotropy. Fluid thixotropy refers to the phenomenon that the microscopic network structure changes with shear time under the action of external force, and macroscopically shows shear thinning. At present, there is no unified explanation for the mechanism of various thixotropies, and domestic and foreign scholars are still in the research stage, but it is an undeniable fact that nano calcium carbonate can improve the thixotropy of RTV silicone rubber.