Cationic cellulosic derivatives as flocculants in papermaking

Water-soluble cationic cellulose derivatives were synthesized by three different procedures, cationizing bleached hardwood kraft pulp with (3-chloro-2-hydroxypropyl) trimethylammonium chloride. The first procedure involved a previous depolymerization step with orthophosphoric acid. The second one consisted on dissolving cellulose in NaOH/urea before cationization. For the third procedure, the reaction medium was heterogeneous since it was carried out with a part of cellulose with high degree of polymerization. Oppositely to the common methods, cationization occurred under mild conditions. Differences among the three derivatives are illustrated by X-ray diffraction patterns of pretreated samples, infrared spectra, and determinations of the degree of substitution, the zeta potential, the charge density and the molecular weight. The performance of these polyelectrolytes for the flocculation of mineral fillers used in papermaking was tested by laser diffraction spectrometry. The flocculant with the highest degree of polymerization and charge originated the best results, particularly when the filler used was kaolin, proving that water-soluble cationic cellulose derivatives can aid in the flocculation of fillers used in papermaking. On the contrary, the shortest-chained derivative was not effective. The results were interpreted in terms of the characteristics of the cellulose derivatives flocculants and of the fillers, and neutralization and patching were proposed as the dominant mechanisms.