Effect of zeta potential on retention and drainage of secondary fibres

The experiments have been carried out in the laboratory to investigate the interactions among negatively charged fibres, fines and positively charged polymer particles on two different papermaking slurries of old corrugated containers (OCC) pulp and mixed office waste (MOW) paper pulp. The effects of different wet-end chemicals such as polyacrylamide, polyamide amine and polyethylene amine on fibre surface chemistry have been followed by electrokinetic measurements (zeta potential) of papermaking stock to control the retention and drainage and see how well they perform in the wet-end of the paper machine. The flocculation behaviour has been investigated by different procedures: dewatering test and measuring the first pass retention. Treatment of pulps with chemical additives resulted in substantial improvement of drainage with increase in first pass retention. For OCC pulp, the best results were obtained with 0.5% polyacrylamide improving the drainage by 82% with corresponding first pass retention of 87.5% against 81.8% for the control pulp. However, for MOW pulp, the best results were obtained with 0.3% polyethylene amine improving the drainage by 63% with corresponding first pass retention of 86.0% against 74.2% for the control pulp. The studies on zeta potential of secondary fibres revealed the dependence of first pass retention and drainage on zeta potential of pulps. As the zeta potential approaches zero, the conditions approach optimum for first pass retention and drainage. This way, zeta potential control can lead to environmental protection and competitiveness by using secondary fibres more extensively.