Cationic Microparticle Retention Aids: The Mechanism Study and Laboratory Evaluation

The cationic polymeric microparticles (CPMP) with different charge densities and particle sizes were synthesized and characterized.The flocculation and retention of precipitated calcium carbonate {PCQ and titanium dioxide {TiO2) suspensions induced by a cationic polymeric microparticle retention system were studied in both the original and washed pulps. For the dispersion of PCC in the washed pulp, the CPMP alone is not an effective retention aid because both the CPMP and PCC are positively charged. However, the retention of fillers can be significantly enhanced by dispersing FCC in an unwashed pulp. The combination of CPMP and a high- molecular weight, water-  soluble polymer led to excellent retention of PCC. Although both anionic or cationic polymers can be used in conjunction with CPMP, different mechanisms are involved in these dual-retention systems. For the dual-retention system of CPMP-APAM (anionic polyacrylamide), it is believed that a bridge is formed between the CPMP patch and APAM . In contrast to the CPMP-APAM system, the increase in the filler retention efficiency by the dual-retention system of CPMP-CPAM (cationic polyacrylamide) is not through the bridging formation between CPMP and CPAM, but is caused by the configuration change of the cationic polymer in the presence of CPMP. It is believed that the pre-adsorption of CPMP can prevent CPAM from getting flat on the solid surface, resulting in an extended polymer conformation and high retention efficiency. It has also been found that the particle size of a cationic polymeric microparticle is a critical factor affecting the PCC retention.