Research progress of nanometer calcium carbonate in RTV silicone rubber
Room temperature vulcanized silicone rubber is widely used as an adhesive, sealant, potting and molding material, and has its use in various industries. Among them, the reinforcing filler has a very important influence on the rheological properties and mechanical properties of RTV silicone rubber. Nano-calcium carbonate has the characteristics of low price, excellent performance, large filling capacity, non-toxic and tasteless, and can be widely used as a reinforcing filler for RTV silicone rubber.


There are two disadvantages of using nanometer calcium carbonate directly in silicone rubber: First, the specific surface area of nanometer calcium carbonate is large, intermolecular force, electrostatic interaction, hydrogen bonding, etc. cause agglomeration of calcium carbonate powder, plus nano calcium carbonate as a pro The aqueous inorganic compound has poor affinity with the organopolysiloxane and easily forms powder aggregates, resulting in uneven dispersion of the nano calcium carbonate in the system. Second, the nano-calcium carbonate has a high oil absorption value, and the thickening effect on the silicone rubber system is remarkable, and the thixotropic property is poor, which affects the construction performance of the silicone rubber. Therefore, it is necessary to modify the surface of nanometer calcium carbonate according to the characteristics and requirements of RTV silicone rubber, which can solve the defects of the system caused by ordinary nano calcium carbonate, such as easy flow, poor extrusion and low strength.

Nano-calcium carbonate modification technology:
The modification of nanometer calcium carbonate is mainly modified by wet method. Specifically, a dispersant and a surfactant are added to the nanometer calcium carbonate slurry, and the particle size and surface activation rate of the nanometer calcium carbonate are controlled by the process, and finally, dehydration, drying, pulverization and The modified nano calcium carbonate is obtained after classification.


At present, the most used and most effective surfactants are mainly fatty acid organic compounds. One end of the compound molecule is a polar group such as a carboxyl group or an ether group, which can undergo physicochemical adsorption or chemical reaction with the surface of the calcium carbonate particle to form a stable bridging structure; the other end of the molecule is a long-chain alkyl group, and the structure Similar to polymer molecules and thus has good compatibility with organic polymers. After surface modification, the nanometer calcium carbonate can greatly enhance the interfacial adhesion between the nano calcium carbonate particles and the organic high polymer, and effectively reduce the oil absorption value of the nano calcium carbonate and reduce the viscosity of the nano calcium carbonate/organic high polymer system. Improve dispersibility and increase the amount added.

Effect of Nano Calcium Carbonate on Mechanical Properties of RTV Silicone Rubber

The unreinforced RTV silicone rubber has low strength and poor elongation, which cannot meet the mechanical properties of many applications. The reinforcing mechanism of nano-calcium carbonate in RTV silicone rubber is similar to that of nano-particles in polymer. The tensile strength of unreinforced RTV silicone rubber is about 0.35 MPa. After reinforcing with nano-calcium carbonate, RTV silicone rubber The strength can reach 1~2 MPa, and it is reinforced by RTV silicone rubber filled with nano-calcium carbonate. There are many kinds of silicone molecules, between fillers and between silicone molecules and fillers. The chemical and physical interactions have greatly improved the performance of silicone rubber.


According to the experimental results obtained, Peng Ya learned that the interaction between nano-calcium carbonate and room temperature vulcanized silicone rubber is mainly physical adsorption, which is different from the chemical interaction of fumed silica and silicone rubber to form hydrogen bonds. The mechanism of nanometer calcium carbonate reinforcement is proposed. The physical adsorption effect of nanoparticles: when the amount of filled nanoparticles reaches a sufficient amount, the viscosity of the filler compound is greatly increased, and the interaction of nanoparticle aggregates is facilitated by shearing. The increase in the number of points increases the crosslink density, thereby improving the mechanical properties of the room temperature vulcanized silicone rubber and embossing the reinforcing properties of the nano calcium carbonate.


Liu Fei et al. analyzed the phase composition and particle structure, morphology and particle size distribution of nano-active calcium carbonate by X-ray diffractometer, scanning electron microscope and laser particle size distribution analyzer. Several primary particle sizes were similar and different. Effect of particle size nano-active calcium carbonate on mechanical properties of deketoxime-type one-component room temperature vulcanized silicone sealant. The results show that the secondary particle size of the calcium carbonate with a small primary particle size after surface treatment is not necessarily small, and the secondary particle size has a greater influence on the mechanical properties of the RTV silicone sealant than the primary particle size; The decrease in diameter (rather than the reduction in primary particle size), the tensile strength, elongation at break and hardness of RTV silicone sealant increased.


Lu Guozhang completely saponified stearic acid and then added coconut oil to stir evenly. The obtained mixture was used as a modifier of nano-calcium carbonate. The nano-CaCO3 particle size was 60-80 nm. The product was applied to silicone sealant to reinforce its strength. It has an excellent appearance and reinforcement up to 1.40~1.55 Mpa.


Luo Suilian et al. used a self-made ultra-fine calcium carbonate suspension to coat silica on the surface of calcium carbonate, and then hydrophobized the CaCO3/SiO2 composite particles with an organosilane coupling agent, and then modified the coupling agent. The calcium carbonate composite particles are applied to the one-component room temperature vulcanized silicone rubber. The results show that the modified calcium carbonate composite particles are more uniformly dispersed in the rubber, and the tensile strength of the RTV silicone rubber filled with the calcium carbonate composite particles is filled with fatty acid. The treated calcium carbonate is more than twice as much, and the calcium carbonate composite particles have better reinforcing properties.