Date of Award

Spring 1978

Document Type

Dissertation

Degree Name

Doctor of Engineering Science in Civil Engineering

Department

Civil and Environmental Engineering

First Advisor

John W. Liskowitz

Second Advisor

Angelo J. Perna

Third Advisor

Thomas J. Olenik

Fourth Advisor

Robert Dresnack

Fifth Advisor

Manuel Perez

Abstract

A separation process has been developed which recovers similar paper grades from a mixed stock by selective wettability. This process capitalizes on the various paper additives which are intended to resist water wetting and result in paper flotation. While water can be used to achieve many desirable paper separations, the detention times required are excessive, and therefore, limit any industrial application. Surface-active agents, in low concentrations, can be used advantageously by reducing the detention times for all paper while the structure of the surfactant can be used to selectively recover similar papers over a controlled time period. Detention times have been established with several ionic and non-ionic surfactants over various concentration ranges. The surface and capillary wetting processes have been determined for a number of different commercial grades including catalog, foodboard, kraft shipping sacks, and others. The governing parameters which were found to retard quiescent water wetting included fiber surface charge, coatings, chemical pulping, sizing agents, wet-strength additives, and basis weights. While all surfactants accelerate paper wetting, the charge of the surfactant is critical in determining a desirable separation scheme. In low concentrations, cationic surfactants effectively separate bleached from unbleached papers; anionic surfactants lowered the detention times of unbleached kraft papers when separated from bleached kraft papers. While non-ionic surfactants accelerate all paper wetting, they are non-specific in separations. From measurements made on the transmittance of cationic surfactants through bleached papers, the surface spreading coefficients were found to be proportional to the detention times. Consequently, at a specific surfactant level the liquid penetrates the pores dispelling the entrapped air so that different grades wet and sink at distinctly different times readily allowing separation. A dynamic batch plant system has been studied which significantly increases the through-put that can be achieved under quiescent settling conditions. It was found that neither paper size nor paper shape had any appreciable effect on the detention times when using this recovery process. Lower detention times could be achieved by increasing surfactant concentrations, the mixing agitation, and the power input, or by reducing the loading rates. This paper recovery process can be used in secondary fiber operations to achieve higher fiber yields resulting in a savings of labor and virgin timber, and a reduction in the solid waste problem.

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