Interactions of thermo mechanical pulp fractions with high molar mass cationic polyacrylamides: Part 2. Flocculation

A focused beam reflective measurement device was used to study the flocculation of three different fractions of thermo mechanical pulp. Three high molar mass linear chain cationic polyacrylamides of different charge densities were used as flocculants. The polyelectrolyte dosage and stirring speed was altered, and the change in the particle size was recorded. It was found that the type of pulp fraction significantly affected the flocculation process. Especially the short fraction had unique flocculation properties in comparison to the long fraction. The shear rate was also an important factor determining the flocculation phenomena. Under low shear conditions flocs developed and degraded slower but were more sensitive to overdose than under high shear conditions. By utilizing the fractionation of pulp suspension, and by optimizing the polyelectrolyte type and dosage individually for each fraction, new possibilities for industrial process enhancement can be introduced.