Synthesis and application of cationic spherical polyelectrolyte brushes as retention and drainage aid in bleached eucalyptus kraft pulp

In the present study, a series of cationic spherical polyelectrolyte brushes (CSPB), consisting of a silica core and a shell of copolymer of acrylamide (AM) and [2-(methacryloyloxy)ethyl] trimethylammonium chloride (METAC), were synthesized. Then a dual-component system which was composed of CSPB and anionic polyacrylamide (APAM) was used to improve the retention and drainage properties of bleached eucalyptus kraft pulp and precipitated calcium carbonate (PCC). Comparative researches about retention and drainage properties between CSPB/APAM system and cationic starch/APAM system were undertaken as well. Results showed that further improvement in first-pass retention (FPR) of pulp, FPR of PCC and drainage time could be achieved by CSPB/APAM system. It was also found that increase of shear intensity led to a decrease in retention efficiency, while it had no significant influence on drainage time of pulp. However, due to the symmetrical or quasi-symmetrical spherical brush structure, CSPB still showed better retention efficiency than cationic starch under different turbulent conditions. Furthermore, the flocculation mechanism of the CSPB/APAM dual-component system was proposed in the paper.