INTERACTIONS OF MICROFIBRILLATED CELLULOSE AND CELLULOSIC FINES WITH CATIONIC POLYELECTROLYTES

The overall aim of this work was to produce and characterize different types of cellulosic fines and microfibrillated cellulose; to study their interactions with high molar mass cationic polyelectrolytes; and to demonstrate novel examples of their utilization. The work was performed, and its results discussed mainly from papermaking point of view, but the results are also well applicable in other fields of industry. Cellulosic fines are an essential component of papermaking fiber suspension. Microfibrillated cellulose can be considered as a sub fraction of cellulosic fines, produced by disintegration and dispergation of wood fibers to fibrillar level. High molar mass cationic polyelectrolytes are commonly used to improve fines retention in consolidating fiber network. Thus, their interactions with fines have a significant role in modern papermaking. As the different fractions obviously have unique characteristics, it can be surmised that their interactions with polyelectrolytes are dissimilar. Four fines fractions, three fiber fractions and four microfibrillated cellulose fractions were produced. Their physical and chemical characteristics were determined among others by X-ray photoelectron spectrometry, atomic force microscopy, cryogenic transmission electron microscopy, ultracentrifugation and turbidimetry were used. Six different cationic polyacrylamides and one cationic starch were used as flocculants. The adsorption of the polyelectrolytes on the cellulosic fractions was measured by polyelectrolyte titration method. The flocculation behavior of these components was studied with multiple light scattering apparatus and focused beam reflectance measurement device. This work shows that, since the different fines fractions have specific properties, they have individual flocculation and adsorption behaviors with high molar mass cationic polyelectrolytes. It was also shown that the retention and adsorption of clay particles is dependent on the properties of the fiber fraction. In addition, by optimum combination microfibrillar cellulose and cationic starch it is possible to enhance the strength properties of paper without simultaneously deteriorating the drainability of the pulp suspension.