Study On Synthesis Of Amino Acids Grafting And Silica Coating Nano Calcium Carbonate

Nanometer calcium carbonate (CaCO3) is a widely used inorganic filler, but because of small size, high surface energy, strong hydrophilicity and poor acid resistance, it must be modified in the application process.The experiment selected amino acids and silicon dioxide to surface modification of nano CaCO3, prepared modified nano CaCO3,explored and optimized the reaction conditions.By adding amino acids in nano CaCO3 slurry, it can introduce active groups such as carboxyl and amino on the surface of nano CaCO3 to realize the surface modification. The mechanism of the modification was studied by FTIR, XRD and TGA etc.. Results indicate that L-lysine and Glutamic acid is in the form of chemical grafted onto the surface of nano CaC03.Glutamic acid modification is better than that of L-lysine. New diffraction peak did not appear before and after modification. The diffraction peak intensity of amino acid modified nano CaCO3 is decreased obviously. The diffraction intensity peak strength of Glutamic acid modified sample is lower than L-lysine modified sample.The carbonation method made nano CaCO3, the average particle size of nano CaCO3 is about 55nm with the calcite structure, crystal structure and high degree of crystallinity. The optimum process conditions of L-lysine amino acid grafting nano CaCO3 is ultrasonic for one hour, water as the solvent,CaCO3 slurry concentration 8～10wt%,the dosage of L-lysine m(L-Lys):m(nano CaCO3)=10wt%, temperature 70 ℃, modification time of 70min and stirring speed of 800rad/min.Under the optimized condition, the activation degree of modified nano CaCO3 is 46.9%, the oil absorption value is 42.37g/100g.The optimum conditions of Glutamic acid modifying nano CaCO3 is slurry concentration CaCO3 10wt%, m(Glutamic acid)/m(CaCO3)=10wt%, modification temperature 90℃, modification time of 100min. Under the optimized conditions, the activation degree of modified nano CaCO3 is 86.07%, the oil absorption value is 23.64g/100g.The CaCO3/SiO2 composite was prepared by by-product fluosilicic acid in the phosphate fertilizer industry, ammonia and nano CaCO3 as raw materials. Experiments determined the optimum condition of SiO2 coating CaCO3 is that the reaction temperature is 60℃, the mixture ratio of m(SiO2)/m(CaCO3)=8wt%, the reaction pH value is at the end of 9, the aging time is more than 8h.Under the optimum conditions, the CaCO3/SiO2 complex 24h buffer solution of c(Ca2+)= 0.014mol/L, acid resistant performance is good, the acid resistance of nano CaCO3 coated increased significantly. Under the suitable conditions of coating products, results of FTIR, XRD and particle size analysis show that SiO2 chemically bonded with CaCO3,SiO2 as amorphous coated on the surface of nano CaCO3. After coated, the size of nano CaCO3 particle decreases and the average particle size is 44.67nm.