Flocculation and retention of fillers with nanocelluloses

The objective of this study was to examine the effect of different cellulose nanofibrils (CNF) on the flocculation and retention of precipitated calcium carbonate (PCC) and kaolin. Of particular interest was the study of how charge modifications of CNF affect its flocculation and retention capacity. The results clearly show that different CNFs can be used as flocculants and retention aids. However, CNFs have to be chemically modified (high charge density) in order to increase their electrostatic interactions with particles and other additives, and hence boost flocculation. Furthermore, the flocculation and retention efficiency is significantly improved when charge modified CNFs are combined with polyelectrolytes. It is probable that the presence of polyelectrolytes can strengthen and induce formation of CNF/polyelectrolyte bridges between filler particles, leading to efficient flocculation. Charge modified CNF could be used to increase filler retention up to 95% in both one and two component systems. The maximum retention was strongly dependent on the charge density of CNF in a two component system and on the polyelectrolyte concentration used.