Study On Synthesis And Modification Of Calcium Carbonate Used For Paper Making

The use of fillers in papermaking process can provide cost savings remarkably and improve paper brightness. But the use of fillers will affect the combination between the fibers in the paper, which lead to the reduction of paper strength and limit the application of fillers. In order to reduce the negative effects the use of fillers for paper, modification was carried out on the packing is necessary.First of all, we research the synthesis of precipitated calcium carbonate in this study, the effects of the concentration of calcium hydroxide, carbonization temperature and the flow rate of carbon dioxide on the size of products were investigated. The changes of conductivity and pH value in the carbonation process were recorded and analyzed. After that, use ammonium sulphate as precipitant and the mixture of starch and sodium stearate to modify calcium carbonate.In the synthesis process of precipitated calcium carbonate, the temperature of carbonation reaction has the largest impact on the size of precipitated calcium carbonate than the concentration of calcium hydroxide and the flow rate of mixed gas. When the temperature of carbonation reaction was 20℃, the concentration of calcium hydroxide was 4% and the flow rate of mixed gas was 400mL·min-1, the quality of the precipitated calcium carbonate conform to the occupation standard HG/T 2226-2010.The method which use the compounds are obtained by reaction of starch and sodium stearte, using ammonium sulfate as precipitant forms a layer of starch deposition film on the surface of calcium carbonate. Starch and sodium stearate coating modification process of calcium carbonate was investigated. We use the strength properties of papers which were produced by bagasse and use modified calcium carbonate as filler as reference index, determine the better modification reaction conditions by single factor experiment and analyze the modified calcium carbonate by SEM. The results indicate that the optimum conditions that when the dosage of starch is 30% of the mass of calcium carbonate, the dosage of sodium stearate is 5% of the mass of calcium carbonate, the holding temperature is 90℃, soaking time is 1 h, and the rate of stir is 500rpm, the modified PCC filled paper has good strength and brightness. The brightness was 79.6%, tearing index was 9.3mN·m2·g-1, burst index was 1.22 kPa·m·g-1, when the amount of filler was 20% of bagasse.Finally, modified PCC filler retention rates and the performance of paper using filler were studied. The result shows that the retention rate of modified calcium carbonate higher than unmodified calcium carbonate 7.28%. With the increase of loading quantity, filler retention reduced. Compared with the paper which contain unmodified precipitate calcium carbonate, the average tearing index increased 1.79 mN·m2·g-1, the average burst index increased 0.24 kPa·m·g-1, and the average brightness increased 3.2%. Observing the paper’s surface by SEM, we can see that the unmodified calcium carbonate’s retention with the help of Mechanical entrapment, but the modified calcium carbonate adsorbed on the fiber surface, enhance the retention rate.