Date of Award
Bachelor of Science
Paper Science and Engineering
Dr. Raymond L. Janes
A review of retention is presented. Included are discussions concerning retention mechanisms, variables which affect retention, variables affected by retention and various retention aids. A detailed experimental procedures involving the use of the dynamic retention/drainage jar is included along with several modifications of the apparatus.
The purpose of the experimental work was to study the effects of polymer molecular weight on retention and the bridging mechanism. Two cationic retention aids of low and high molecular weight along with two non-ionic "bridging agent" retention aids were employed. Various combinations of these chemicals were studied at different levels of addition and under different shear conditions. The results are discussed as they relate to maximum retention, maximum retention and level of addition, percent improvement at various levels of addition, shear and shear resistance.
It was found that in most cases higher molecular weight retention aids give higher retention than lower molecular weight retention aids. High molecular weight polymers are more efficient than low molecular weight polymers at high shear but less effective than the low molecular weight bridging agent regardless of shear. Increasing molecular weight gives increased stability to retention reduction by shear. Bridging does occur and increases with increasing molecular weight, to a point. Molecular weight and charge are both important in bridge formation.
Bergeron, Joseph A., "The Effects of Polymer Molecular Weight on Colloidal Retention and the Bridging Mechanism" (1978). Paper Engineering Senior Theses. 57.