Date of Award

4-1989

Degree Name

Bachelor of Science

Department

Paper Science and Engineering

First Advisor

Dr. Raymond Janes

Abstract

Aluminum sulfate, commonly know as alum, undergoes hydrolysis when placed in water and a variety of aluminum species are produced. The ionic charge of the species is dependent on pH. Research has shown that maximum adsorption occurs in the presence of Al8 (OH)20+4. Alum competes with other positively charged particles such as cationic starch for adsorption sites on fibers. Starch charge density and molecular weight govern the extent to which cationic starch adsorbs and bridges to fibers. This project is a study of the influence of cationic starch molecular weight and charge density, and aluminum species on retention.

The variables in the study were aluminum species (pH), starch molecular weight, and starch charge density. The pH levels were 3.5, 4.7, and 5.0 to produce the aluminum species Al+3, Al8(OH)20+4, and Al(OH)3 respectively. Starch loadings that produced zero zeta potentials were determined for each set of conditions by using a zeta potential meter. The starch loadings were then used in Dynamic Britt Jar Retention Tests at their respective pH levels. A zeta potential of zero is believed to create conditions for optimum retention.

The results of this thesis suggested that maximum retention may occur near the pH of 4.7, that is, in the presence of Al8(OH)20+4. In addition, it appeared that as pH increased the bridging mechanism became the dominant mechanism in producing optimum retention. Also, in the absence of alum, high molecular weight starch appeared to be necessary for obtaining retention of acceptable levels. This suggested again the importance of the bridging mechanism.

The key outcome of this study was that the prediction made by Crow and Stratton was supported, that is, as aluminum adsorption increases the starch configuration changes to one of loops and tails. The configuration thereby creates conditions more suitable for bridging and therefore, increased retention.

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