Delamination and flocculation efficiency of sodium-activated kaolin and montmorillonite

In papermaking, a microparticulate retention aid system comprising bentonite and high molecular weight cationic polymer is used to incorporate mineral pigments in the fiber web. It is believed that the mechanism by which bentonite operates is based on its ability to form a bridge between polymer-covered fibers and fine particles, i.e. a microparticulate retention aid system promotes heteroflocculation. The performance of kaolin clay and montmorillonite in the role of microparticles was evaluated by observing the deposition of a calcium carbonate pigment on kraft fibers suspended in water. Neither was found to be effective. However, upon treatment with sodium-rich solutions, the montmorillonite delaminated and calcium carbonate deposition increased considerably. The kaolin clay showed only a small degree of delamination after treatment and, as a consequence, calcium carbonate deposition increased only marginally. When commercial bentonite was treated with a strong acid, its particle size increased resulting in decreased deposition of calcium carbonate on fibers. The overall behavior indicates that the flocculation efficiency of montmorillonite microparticles is related to its ability to delaminate.