PEO-induced flocculation of fines: effects of PEO dissolution conditions and shear history

Abstract

We have studied one of the retention aid systems used in the retention of fines in mechanical grade furnishes, the dual component system consisting of polyethylene oxide (PEO) and a cofactor. The efficiency of the retention aid was determined from fines flocculation experiments in a stirred beaker. It was found that the fines flocculation efficiency depended strongly on how the PEO solution, used in the experiments, was prepared. The way PEO was dissolved (stirring time and intensity during dissolution), stored (storage time and concentration), and injected in the flocculation vessel (shear conditions and dilution), all affected the efficiency to various degrees. The results are interpreted in terms of entanglements of PEO molecules. When PEO granules are dissolved in water, PEO is not instantaneously dissolved as single individual molecules, but initially PEO is present in the form of entanglements. These entanglements become smaller with time and shear. In general, entanglements are more efficient in flocculating fines than freely dissolved molecules. The implications for fines retention on a paper machine are discussed.