Effects of System Closure on Retention Aids for SC-Grade Manufacture, 2002 Technology Summit Proceedings

Marco Polverari, Bruce B. Sitholé, Lawrence H. Allen

As the degree of mill system closure increases, how well will currently available retention and drainage aid systems function in mechanical printing grade mills? In previous reports, we investigated the effects of system closure on retention aid performance in hydosulfite-brightened thermomechanical pulp for newsprint. In this report, we examine the use of a series of retention aids for applicability to system closure when using peroxide-brightened TMP pulp. We measured the performances of 12 different types of retention and drainage aid systems in the laboratory at three simulated levels of system closure. In this work, we have defined the degree of system closure in terms of fresh process water make-up to the mill. The levels of system closure were 55, 20, and 3 m3/t. The results also confirmed that, with increased system closure, the increase in dissolved substances concentration tends to result in a poorer performance of cationic polyacrylamide (CPAM) polymers and PEO enhancers. The choice of the correct enhancer for PEO was important. We found that the best performing CPAMs were those with high molecular weight and high charge density. Coagulants tended to have neutral to slightly negative effects on retention and drainage. Bentonite retention systems performed less well with increasing system closure.