PRECIPITATED CALCIUM CARBONATE (PCC) - CELLULOSE COMPOSITE FILLERS; EFFECT OF PCC PARTICLE STRUCTURE ON THE PRODUCTION AND PROPERTIES OF UNCOATED FINE PAPER

This work examines the precipitation of PCC - pulp composite fillers with varying crystal habits and their effects on the papermaking properties of printing and writing paper. Colloidal (c-PCC), rhombohedral (r-PCC), and scalenohedral types (s-PCC) of composite PCCs were produced and compared with commercial reference PCCs. Scanning electron microscopy showed the c-PCC to be a high-surface-area nano-structured PCC. The rhombohedral composite was formed in clusters like a spider-web structure. Under similar experimental conditions, composite PCC was formed as individual ellipsoidal crystals and some of the particles had malformed structure, in contrast to the structured reference s-PCC. The co-precipitation and the structure of PCC significantly influence the forming, consolidation, and properties of paper, as well as its performance in printing. Composite c-PCC showed the highest retention during forming. At higher filler contents, dewatering was reduced significantly with handsheets containing s- and r-PCC composite fillers. Colloidal composite handsheets showed the lowest tensile index and internal bond strength, while the rhombohedral composite gave the highest z-directional bond strength. Compared with the traditional reference samples containing commercial PCCs, paper with s- and r-composites had significantly higher density but similar light scattering ability. Addition of fibrillar fines to fine paper increased print rub fastness significantly in both laser and inkjet printed samples.