Studies on interactions between aluminum compounds and cellulosic fibers in water by means of 27Al-NMR

Abstract

Interactions between pulp fibers and aluminum compounds in pulp suspensions were studied using fibrous cellulose (FC) and fibrous carboxymethylcellulose (FCMC) powders as models of pulp fibers by X-ray fluorescence analysis and 27Al nuclear magnetic resonance. When deionized water was used at pH 4-5, water-soluble cationic aluminum species (Al3+, aluminum oligomer, and polyaluminum species) were adsorbed on the solid FCMC, forming carboxylic acid aluminum salts by cation exchange. The formation of these nondissociated pulp-COOAl type structures in paper sheets may contribute to some decreases in hydrophilic property. On the other hand, the water-soluble cationic aluminum species had nearly no interactions with hydroxyl groups of solid cellulose in the suspensions at pH 4-5. When tap water was used at pH 5-7, some aluminum components were retained on not only FCMC but also the FC sample. Probably, water-insoluble Al(OH)3 flocs are formed in the suspensions at pH 5-7 and retained on the FC sample by simple filtration effect. Therefore, two mechanisms of the aluminum retention (i.e., electrostatic interactions and a simple filtration effect) may exist between pulp fibers and aluminum components in the practical papermaking process.