The Structure and Strength of Flocs of Precipitated Calcium Carbonate Induced by Various Polymers Used in Papermaking

Abstract

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.