Application of nanostructured titanium dioxide pigments in paper coating: a comparison between prepared and commercially available ones

Nano-TiO2 pigments in pure crystallographic anatase and rutile phases have been successfully prepared by hydrothermal at 120°C and hydrolysis methods, respectively. The laboratory-prepared pigments were characterized parallel to two commercial pigments of the same crystal structure. All pigments were applied in paper coating mixtures, and their influence on coated paper properties was systematically investigated. X-ray diffraction investigation showed that the laboratory-prepared pigments using the hydrothermal method at 120°C were pure anatase, whereas hydrolysis method produced pure rutile phase pigment. The application of the prepared nanopigments and the corresponding commercial TiO2 phases in paper coating revealed that clay/rutile nano-TiO2 pigments in paper coating mixture decreased coated paper roughness more than blending clay with anatase nano-TiO2 pigments. Commercial nano-TiO2 pigments increased porosity of coated paper at both the 30% and 50% addition of nano-TiO2 pigments to clay, while laboratory-prepared nano-TiO2 pigments highly decreased it at 30% addition of nano-TiO2 to clay, compared to clay only. Blending of clay/nano-TiO2 pigments improved both brightness and opacity of the coated paper where commercial pigments are more effective. Burst, tensile strength, stretching, and TEA were improved in the case of all pigments. The 50% addition of the prepared and commercial nanopigments in conjunction with clay improved the mechanical coated paper properties more than 30% addition (except the cases of stretching and TEA of the commercial pigments). The coated paper samples were offset printed. It was found that blending of clay/nano-TiO2 pigments improved print density. Commercial nano-TiO2 pigments improved print gloss more than the laboratory-prepared ones. This result was found consistent with the results of coated paper roughness.