Enhancing paper properties by preflocculation of talc using amphoteric starch

The inorganic fillers added to the paper interfere in the inter-fibre bonding and decrease the paper strength. They could not be added beyond a certain limit due to decreased paper strength and machine runnability. The talc filler was preflocculated using different doses (0.1 to 0.8%) of commercial amphoteric starch. The cooked amphoteric starch was added to talc slurry under controlled conditions. The preflocculated talcs were added to the bleached mixed hardwood kraft pulp to produce the laboratory handsheets targeting the varying ash content (15 to 24%). The particle size distribution, micro images and colloidal charge of the preflocculated talcs were measured and compared with the native talc. The filler retention, tensile, burst, tear, Z-direction tensile strength, bending stiffness, air permeability, scattering coefficient, opacity and brightness of sheets made using preflocculated talcs were compared to those of native talc. The particle size of preflocculated talc was increased up to 174%. Relatively higher filler retention and paper strength, and comparable opacity were obtained with amphoteric starch preflocculated talc compared to the native talc. SEM images of the sheets were also taken to understand the distribution pattern of preflocculated and native talcs within the sheet.