Effect of polyelectrolytes on the degree of flocculation of papermaking suspensions

The effects of the surface charge type and density of polyacrylamides (PAMs) on the turbidity reduction, zeta potential, settling rates, floc sizes and effective floc density of papermaking suspensions were investigated at different pH values. Cationic C496 and C492, anionic A130LMW and non-ionic N130 PAMs were used in this study. At optimum dosage, anionic A130LMW PAM proved to be the most effective in the residual turbidity reduction among other PAMs investigated in this work. In contrast, the non-ionic N130 polyacrylamide showed an adverse effect on the degree of flocculation. On the other hand, the floc sizes were larger in the presence of the anionic PAM than the cationic PAMs due to the repulsive forces between the anionic PAM and particle surface, leading to the formation of open structure flocs of less effective density. The results also show that increasing the cationic surface charge from 10% to 35% reduces the floc size and increases the effective floc density. This work has been very successful in establishing the link between electrokinetic behaviour and the produced floc effective density for the flocculated papermaking-PAM suspensions.