Competitive interactions of dextran sulfate with positively charged particles and polymers

Precipitated calcium carbonate (PCC) was flocculated with cationic polyacrylamide (CPAM) in the presence of dextran sulfate (DS). The charge density of the CPAM had little effect on the extent of flocculation. The effect of changing the order of addition of DS and CPAM was studied, including premixing CPAM and DS before addition of DS. Results were discussed in terms of competition of the particles and CPAM for the DS, and then compared with results obtained using suspensions of TiO2 and cationic latex with added DS. These systems contain a much smaller amount of bound DS as compared to free, and the charge density of the CPAM determined the extent of flocculation able to be achieved.