  Modification of calcium carbonate particles with surfactant significantly
improves the properties of the calcium carbonate coating on paper. Unmodified
and CTAB and oleate-modified calcium carbonate nanoparticles were prepared
using the wet carbonation technique for paper coating. CTAB (cationic
surfactant) and sodium oleate (anionic surfactant) were used to modify the
size, morphology, and surface properties of the precipitated nanoparticles. The
obtained particles were characterized by XRD, FT-IR spectroscopy, zeta
potential measurements, TGA and TEM. Coating colors were formulated from the
prepared unmodified and modified calcium carbonates and examined by creating a
thin coating layer on reference paper. The effect of calcium carbonate particle
size and surface modification on paper properties, such as coating thickness,
coating weight, surface roughness, air permeability, brightness, whiteness,
opacity, and hydrophobicity, were investigated and compared with GCC calcium
carbonate-coated papers. The obtained calcium carbonate nanoparticles are in
the calcite phase. The morphology of the prepared calcium carbonate
nanoparticles is rhombohedral, and the average particle diameter is <100 nm.
Compared to commercial GCC, the use of unmodified and CTAB- and oleate-modified
calcium carbonate nanoparticles in paper coating improves the properties of
paper. The highest measured paper properties were observed for paper coated
with oleate-modifed nanoparticles, where an increase in smoothness (decrease in
paper roughness) (+23%), brightness (+1.3%), whiteness (+2.8%), and opacity
(+2.3%) and a decrease in air permeability (-26%) was obtained with 25% less
coat weight. The WCA at 10 min was about 112{\deg} for the paper coated with
oleate-modified nanoparticles and 42{\deg} for paper coated with CTAB-modified
nanoparticles compared to 104{\deg} for GCC-coated paper.
