Distribution of Al, Ca, Si and Mg components in cross sections of pulp fibers in, paper sheets

Distributions of aluminum, silicon, calcium and magnesium components derived from wet-end additives and paper mill water in cross sections of pulp fibers and commercial papers were measured by means of a scanning electron microscope (SEM) attached with an energy dispersive X-ray (EDX) analyzer. The results for laboratory sheets prepared from pulp suspensions by adding 0.5% (on dry weight of pulp) aluminum sulfate or 1.04-1.45% polyaluminum compounds showed that aluminum components were homogeneously distributed in the cross sections of the fibers. Probably not only low-molecular-weight cationic aluminum species but also most cationic polyaluminum components including aluminum hydroxide colloids can penetrate pulp fibers, and are fixed there probably by electrostatic interactions in pulp suspensions. A commercial wood-free office paper containing CaCO3 filler had a maximum distribution peak of aluminum components at approximately 1 mum from the fiber surfaces, whereas a commercial acidic newsprint had a roughly even aluminum distribution. Silicon and magnesium components were distributed in a similar pattern to aluminum in the commercial office paper. Therefore, silicate and magnesium ions originally present in mill water are likely to be retained in the pulp fibers as aluminum magnesium silicate compounds in pulp suspensions.