Kimmo Koivunen

Novel nanostructured PCC fillers

New filler and pigment technologies are needed to improve the optical properties of paper. Filler contents in different paper grades are approaching the maximum levels achievable with current papermaking practices. Much work has been done to maximize the light scattering potential of fillers and pigments by modifying their particle size distribution or specific surface area. The refractive index (RI) is an optical constant of pigment, and less attention has been paid to the possibility of increasing this parameter. In the present study, a novel nanostructured filler-grade precipitated calcium carbonate (PCC) pigment was synthesized. Zinc-based nanostructures, physically contacted with the host PCC material, increase the differences in RI between filler-fiber and filler-air interfaces, yielding increased light scattering. The effective RI of the novel filler was measured using a method which combines a multi-function spectrometer with the immersion liquid method. This method enables effective RI measurement from pigment suspensions, irrespective of the shape, size, and nanostructures occurring on the host pigments. When compared to conventional PCC, the results gained with the nanostructured PCCs suggest an increase in the effective RI. When used as filler in paper, nanostructured PCC yields improved light scattering, i.e., better opacity.