The effect of calcium ions on the efficiency of polyethylene oxide–cofactor retention aid systems

Polyethylene oxide (PEO)–cofactor retention aid systems are used in papermaking to improve fines retention in mechanical grade papers and in the control of pitch in process waters. Mill experience has shown that these retention aid systems work less well in furnishes containing a large amount of deinked pulps. Various dissolved and colloidal substances could possibly interfere with the PEO–cofactor complex and make it less effective. One of the compounds that could negatively affect the PEO–cofactor retention aid system is calcium, since deinked pulps can contain calcium carbonate fillers, which dissolve at neutral pH, thus increasing the calcium ion concentration in the whitewater. In this study the effects of calcium ions on fines deposition on fibers and on fines flocculation are examined. It is found that calcium ions can form colloidal-like complexes with the cofactor, which decrease the flocculation efficiency of PEO. The effects can be minimized by adding the cofactor just before the PEO addition.