Starch granules spot-coated with aluminum silicate particles and their use as fillers for papermaking

Abstract

Mineral fillers are among the most important raw materials of paper. In papermaking, a filler is typically mixed as such with the fibrous stock prior to the forming section where it, together with the fibers and fines, forms a paper web with heterogeneous three-dimensional composite structure. The filler is eventually located both in the paper pores and between adjacent fibers. When light interacts with a multitude of solid-air interfaces occurring in such a structure, complicated light scattering effects take place. These effects are essential for appearance development, viz. brightness and opacity. Fillers contribute to these effects by increasing the number of such interfaces. Many fillers also cost significantly less than fibers. Therefore, it is advantageous to introduce as much filler as possible. It is also well known, however, that filler prevents formation of hydrogen bonding and is hence detrimental for strength development. In addition, the legislation of European Union favors increasing recovery of paper and packaging products, e.g., for energy production. However, as a side product of paper waste incineration, significant amounts of ash is formed. Hence it would be advantageous to replace inorganic fillers with combustible organic materials. We have fabricated a novel aluminum silicate spot-coated starch-based filler. The results indicate that when silicate is introduced in paper on the surface of starch granules benefits in light scattering and strength development can be achieved.