The effect of dextran and its derivatives on PEO and PAM-induced calcium carbonate flocculation and floc strength

High molecular weight water-soluble polymers (retention aids) are routinely added to improve filler and fines retention during papermaking. Dissolved and colloidal substances (DCS) associated with mechanical pulps (MPs) are, however, known to interfere with the retention aid functions. Reported in this work are both flocculation results and novel filler-floc strength measurements for precipitated calcium carbonate flocs formed in the presence of model DCS polymers. The DCS models include well-defined dextran, dextran sulfate and hydrophobically modified dextran. Depending on the nature of the retention aid, the model DCS polymers can either interfere with or, in a few cases, improve retention. The results are interpreted in terms of established models of colloid science.