Bentonite delamination induced by pulp fibers under high shear monitored by calcium carbonate deposition

Bentonite in combination with cationic polyacrylamide (cPAM) is used to incorporate mineral pigments (fillers) into paper. It is believed that bentonite acts as a bridge between polymer-coated pulp fibers and pigment and its performance appears to be related to its ability to delaminate. The possibility of enhanced bentonite delamination induced by pulp fibers coated with cationic polyacrylamide was studied. The extent of bentonite delamination was evaluated by measuring the deposition of a calcium carbonate pigment on fibers suspended in water. When a mixture of polymer-treated fibers and bentonite is exposed to high shear before calcium carbonate addition, almost complete bentonite delamination takes place. At low shear, a similar delamination is achieved, but at a much longer stirring time. Adding bentonite to a mixture of untreated fibers, calcium carbonate and cationic polyacrylamide results only in partial delamination, and consequently, more bentonite is required to achieve the maximum calcium carbonate deposition. The results suggest that in this case the bentonite bridge contains on average four montmorillonite platelets.