Abstract: We prepared hydrophobic calciumcarbonate nanoparticles in situ via the carbonation route with various modifiers such as sodiumstearate (NaSt), octadecyl dihydrogen phosphate (ODP), and oleic acid (OA). The modification of CaCO3 was determined by measuring its active ratio, whiteness and the contact angle. The products were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), and transmission electron microscopy (TEM). FT-IR spectra revealed that chemical bond and physical adsorption between modifiers and CaCO3 happened during the modification reaction. The infrared absorption peak of the modified CaCO3 was blue shifted 44 cm-1 compared with the unmodified CaCO3. A preliminary reaction mechanism was discussed in this paper. At a 2%(w(CaCO3)) modifier dosage, the active ratio of CaCO3 as modified by ODP was 99.9%and the whiteness was 97.3%. The contact angle was 122.25° for the CaCO3 modified in the presence of ODP. The theory to support these findings and synthetic methods was presented for these novel materials.

Key words: Calcium carbonate, In situ synthesis, Surface modification