Surface Modification Of Nano-Calcium Carbonate For Non-polar And Polar Systems

Nano-calcium carbonate particles are easy to aggregate in application and not compatible with systems, because of their small particle size and large specific surface area. This paper concerns surface modification of nano-calcium carbonate for non-polar and polar systems. For non-polar systems, such as plastics, rubbers and solvent base paint, etc., calcium carbonate was modified with sodium stearate. The effects of pH value and dispersants were studied. For polar systems, like water, calcium carbonate was modified with three kinds of dispersant. Sedimentation property and rheologic behavior were studied. Calcium carbonate modified with sodium polyacrylate was added to water alkyd paint.As pH value of the slurry increases activation grade decreases quickly at first then becomes constant 2% and oil-absorbed value increases slowly. Activation grade of the sample modified at pH=6.5 adjusted with diluent phosphoric acid is zero and oil-absorbed value is 89.6 gDOP/100g.Consequently, the degree of carbonization should be controlled accurately in production.Activation grade of sample modified with sodium stearate in the presence of dispersant sodium polyacrylate is zero. Sodium polyacrylate molecules can be absorbed on particles, which can induce the decrease of oil-absorbed value. Activation grade of sample in the presence of dispersant polyethylene glycol is 49.6%.Sedimentation property of calcium carbonate in water was improved by dispersant PAANa and sodium hexametaphosphate. PAANa lowered the viscosity of slurry, and did not affect the thixotropic ratio. The best concentration is about lwt%.More calcium carbonate modified with PAANa was added to water alkyd paint compared with calcium carbonate unmodified. Hardness degree of the film reached to 3H. Although it improved the hardness degree, not all particles were in monodisperse state.