Flocculation of clay particles with poorly and well-dissolved polyethyleneoxide

Mill experience has shown that the efficiency with which polyethylene oxide (PEO) retains fines in mechanical grade papers depends on the shear histor y of PEG. To show that the state of dissolution of PEO affects its efficien cy as a retention aid, we performed model flocculation experiments with cla y, using PEO and a PEG-cofactor retention aid system. We found that the per formance of PEO depends strongly on how the PEO is dissolved in water: The ability of both the PEO and the PEG-cofactor systems to flocculate clay was affected by the length of the stirring period to which the PEO solutions w ere subjected prior to the flocculation experiments. Freshly dissolved PEO flocculated clay faster than salt (KCL). PEO stirred for an additional hour flocculated clay effectively only at an optimum dosage and slower than sal t. PEO stirred for one day did not flocculate clay at all. However it was o bserved that the presence of a cofactor improved the performance of PEO sti rred for one day. The variations in PEO performance in flocculating clay ar e discussed in light of the changes that PEO undergoes during its dissoluti on in water: Initially PEO macromolecules are entangled and capable of form ing bridges. With time the entanglements, and thus the bridging ability dis appear This view is supported by measuring the pressure drop across a valve caused by the flow of PEO solutions. The pressure drop was observed to als o depend on the length of stirring.