engleski

Preparation of hydrophobic CaCO3 nanoparticles

Calcium carbonate is an extremely versatile filler and pigment that is utilized in a wide variety of products including paper, plastics, rubber and pharmaceuticals. Such a variety of applications requires CaCO_3 to have different physical and chemical properties, among which particle size, specific surface area, morphology and surface characteristics are the most important. Advanced applications of CaCO3 are related to the production of stable homogeneous nanoparticles. However, the incompatibility of mineral hydrophilic surface with the hydrophobic polymers is particular problem. Therefore, the surface of CaCO_3 is often modified by variety of surfactants, among which fatty acids are most commonly used. At industrial scale the most widely used method to obtain CaCO3 is the carbonation route, which consists of bubbling CO2 gas through an aqueous slurry of a Ca(OH)_2 suspension in a batch process. By using a semicontinuous carbonation process it is possible to adjust the supersaturation and to control the morphology and size of precipitated CaCO_3. In this work, we studied the formation of hydrophobic, nanometric, CaCO_3 in the presence of sodium stearate. The semicontinuous process has been explored at 20  C and conductivity set-point at 1.0 mS cm-1 and 7.0 mS cm-1. Samples were characterized by means of FT-IR spectroscopy, TEM and BET analysis. The extent of hydrophobicity of different CaCO_3 samples was evaluated by the floating test. The results showed the decisive role of the excess of suspended Ca(OH)_2 on the formation of the CaCO_3 nanoparticles. Furthermore, sodium stearate does not only change the surface properties of CaCO_3 but also influence the crystal nucleation and crystal growth of CaCO_3.

Precipitation; Calcium carbonate; Sodium stearate; hydrophobicity; nanoparticles

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