Graduate Thesis Or Dissertation
 

Dispersion of pulp slurries using carboxy-methyl cellulose (CMC)

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/kw52jb19q

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  • A novel technology for processing pulp slurries with high inorganic filler content and at high consistencies (solids content) is extrusion. The paper industry waste comprises of fibers mixed with inorganic filler content. Using extruders similar to food extruders and consistencies ranging from 30-45%, profiles can be extruded from this waste and dried into useful products having tensile modulus of 3-6 G-Pa. These strength properties compare well with those of medium density fiberboard (MDF) and high density hardboard. A critical factor in the successful extrusion of pulp slurries is the use of dispersants. In the absence of dispersants, the pulp fibers flocculate, separate from the water and subsequently surge out of the extruder. The final product possesses low integrity and typically cracks upon drying. Carboxy-methyl cellulose (CMC) has been used as a dispersing or deflocculating agent in the paper industry. It has been shown that CMC has the ability to disperse the pulp fibers and promote inter-fiber bonding. In our research we were able to determine the effect of CMC molecular weight on the extrusion behavior of pulp. Two different experimental techniques (macro and micro-rheological) were adopted to corroborate our results and to augment our understanding of this multi-phase system. It was then shown that there exists a definite correlation between the macro and micro-rheological behavior of pulp. In the micro rheological experiments, the typical crossover shear stress at which the viscous modulus (G") exceeds the storage modulus (G') was then shown to related inversely with the CMC molecular weight. Adsorption isotherms were generated to understand the mechanism of torque reduction for each CMC molecular weight. It was shown that reductions in fiber contact friction results from adsorption of CMC on the pulp fibers. We also investigated the effect of ionic strength on the rheological behavior of pulp slurries. However, no significant relationship was obtained. Extrusion of pulp with high inorganic content appears to offer a viable method of minimizing the solid waste generated by the paper industries.
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