Starch-hybrid fillers for paper

Starch-based pigmenting materials with improved optical performance have been prepared in the laboratory scale by the complexation approach. The water-based treatments using soluble, anionic starch derivatives target at insoluble hybrid materials between starch and ions of higher specific refractivity. Polymer derivatives selected from the group of starch phosphate, acetylated starch phosphate, starch citrate and carboxymethyl starch were combined with water-soluble inorganic salts to form insoluble pigmenting materials. The inorganic components were selected from the group of calcium-, barium-, zirconium-, zinc- and titanium-based compounds. The criteria for the selection included efficiency of polymer functionalization as well as the insolubility, yield and optical properties of the hybrid structures. Further evaluation has been made in respect of processability, suitability for cryogenic grinding and potential for paper manufacturing. The resulting precipitates exhibited composite structures and refractive indices depending on the inorganic constituent. In contrast to the inherent refractive index around 1.45 of starch-based materials, refractive indices between 1.50 and 1.55 (using Ca-, Zn- and Ba-components) and closer to 1.60 (using Zr- and Ti-components) have been observed for complexed materials. The prepared materials were characterized for complexation structure and stability and for suitability for filler applications in laboratory scale sheet formation.