When the percentage of ﬁller is increased in paper, the optical properties are improved and the production cost lowered. However, ﬁllers weaken paper strength by decreasing the ﬁbre-ﬁbre bonded area. Little is known about the optimum ﬁller ﬂoc size or ﬁller ﬂoc properties to allow developing optimum paper characteristics. Consequently, the ﬂoc structure and strength of precipitated calcium carbonate (PCC) aggregates was studied using various polymers (ﬂocculants and dry strength agents): by static light scattering/diffraction (SLS), real time ﬂuorescent video imaging, image analysis, photometric dispersion analysis (PDA) and scanning electron microscopy (SEM).
It was found that PEO/cofactor induced PCC aggregates were weaker at high shear and far more irreversible than those induced by the partially hydrolysed polyvinyl formamide copolymerised with acrylic acid (PVFA/NaAA) or C-starch. Flocs produced at low polymer dosages were smaller and weaker than those produced at higher dosages. The number of discrete PCC particles in aggregates was measured using real time ﬂuorescent video imaging combined with image analysis.