Preparation And Characterization Of Silica Coated Calcium Carbonate Composite

Ground calcium carbonate?GCC?is an important filler material.When applied in the plastic and rubber products,it can reduce the cost.However,the GCC is featured by the smooth and angular surface,which resulted in the insufficient reinforcement to the rubber or plastic.Hydrated silica,known as white carbon black in china,is characterized by whiteness,fine particles,and strong interfacial activity.Hydrated silica is an important inorganic additional agent and is mainly applied in rubber industry as reinforcing agent.On account of the problems and characters above,the CaCO₃-SiO₂ composite with core-shell structure was successfully prepared by the aqueous mechano-chemistry method.The main process includes:the dispersion of hydrated silica,the grind and interfacial activation of the GCC,and the compositing of the two ingredients.1)The agglomeration and dispersion of the hydrated silica in water were studied.The hydrated silica is composed of amounts of silica agglomerations.The diameter of the signal particle is about 25nm,but the agglomerate particle is about15?m.The AF?50?of raw silica is 595.64.The disaggregation and well-dispersion of silica is realized by wet grinding method.The coefficient of aggregation AF?50?is decreased from 595.64 to 33.68 and diameter d50 is decreased from 14.981?m to0.842?m,which means the well dispersion of silica.The optimized condition is as follows:the silica concentration is 20%,the ratio of grinding media to material is 5:1,the grinding time is 90 minutes,and the PAAS?sodium polyacrylate?percentage is6%.2)The preparation of powder material featured in core-shell structure CaCO₃-SiO₂ composite.The dispose cause the rougher and less angular surfaces of the GCC.The optimized conditions are as follows:the ratio of CaCO₃ and SiO₂ is 5:5,the time is 40 minutes,the ratio of grinding media to material is 5:1,and the machine's rotate speed is 1600 rpm.The core-shell structure can be observed in SEM.The plant test of this composite is carried out too.3)The application of the composite in the silicone rubber.The silicone rubber reinforced by the composite is prepared.The CaCO₃-SiO₂ composite can enhance the mechanical performance of silicone rubber obviously,whose breaking strength?is0.99MPa,and the elongation at break?is 156.95%.The results is better than the rubber reinforced by GCC and hydrated silica.The enhancement of the mechanical properties is because of the well dispersion and the well interfacial combination of the composite and the silicone matrix.And the anti-UV ability of the composite differs in the different x?the ratio of the SiO₂ to CaCO₃?of the composites.4)The mechanism of the composite's formation was studied.The SiO₂ and CaCO₃ particles both contain facial hydroxyl in the particle surface,which caused the formation of hydrogen bonds.And some of the facial hydroxyl can react to form the chemical bond of Ca-O-Si,which can combine the two particles firmly.And the particle numbers ratio of CaCO₃ to SiO₂ is about 1:10.