Effects of processing on zeta potential and cationic demand of kraft pulps

The zeta potential and cationic demand of various kraft pulps—unbleached, bleached and beaten to different wetness levels—were determined in the laboratory. The magnitude of zeta potential of pulp where the final stage was a lignin degrading and dissolving treatment, such as alkaline extraction or hypochlorite, was lower than that of unbleached pulp. The cationic demand of bleached pulp was lower compared to that of unbleached pulp. Beaten pulps showed larger cationic demands than the unbeaten pulps, which can be attributed to the larger specific surface area of pulp components. Fibres become increasingly electronegative when beaten, and therefore, cationic demand of pulps increases with beating. When the zeta potential method is used with pulp furnishes of different wetness, an almost linear relationship is observed between added polyamine and attained zeta potential. However, the slope of the curve is decreased with the increase in wetness of the pulp.