Effects of system closure on retention- and drainage-aid performance in TMP newsprint manufacture

What will happen to the effectiveness of presently available retention- and drainage-aid systems in newsprint mills as we increase the degree of system closure? Will they continue to function well, or will it be necessary to develop new, more effective aids as the degree of white-water recycling increases? The performance of five different retention- and drainage-aid systems was measured at three degrees of closure in TMP (thermomechanical pulp) newsprint The three levels of fresh water makeup used in this study were 55, 20 and 3 m(3)/metric ton of pulp, representing water usage in older mills, modern mills, and a closed mill system. For the 55 and 20 m(3)/metric ton cases, samples of pulps and paper machine white waters were obtained from existing TMP newsprint mills. For the 3 m3/metric ton case, samples of white water were prepared in our system-closure pilot plant. The five retention-aid systems consisted of bentonite/anionic polyacrylamide (Organosorb/Organopol), polyethylene oxide/phenolic resin, polyethyleneimine (Polymin SKA), Poly(DADMAC) (diallyldimethylammonium chloride), and chitosan. Furnishes with more highly recycled white waters had higher cationic demands. Results suggest that system closure impairs the performance of cationic polymers, while that of the nonionic flocculants was relatively unaffected or improved.