Effect of cationic polyacrylamides on the interactions between cellulose fibers.

The interaction between cellulose fibers in the presence of cationic polyacrylamide (CPAM) was analyzed by rheology as a function of polyelectrolyte concentration, charge density, and molecular weight. CPAM was found to strongly influence the yield stress of cellulose suspensions; low doses of CPAM increased the yield stress, but at higher concentrations the yield stress declined. The charge density of the CPAM was the most significant factor in how yield stress responded to CPAM concentration; this effect was able to be normalized to a master curve by considering only the charged fraction of the polymer. The molecular weight of CPAM samples had some effect at high concentrations, but for lower CPAM doses the yield stress was independent of molecular weight over the range studied. The data suggest that CPAM modifies the interaction between cellulose surfaces via several mechanisms, with electrostatic interactions in the form of charge neutralization and charged patch formation dominating; polymer bridging and steric repulsion also influence the overall balance of forces between interacting cellulose fibers.

Rheology of slurries and environmental impacts in the mining industry.

The world's resource industries are the largest producers of waste. Much of this waste is produced as a fine particle slurry, which is pumped to a storage area, generally at a low concentration, where it behaves like a Newtonian fluid. Simply removing, reusing, and recycling water from the slurry represents a step toward a more sustainable practice in this industry. As the concentration of such a slurry is increased as a result of dewatering, the materials exhibit non-Newtonian behavior, which is characterized by shear thinning, a yield stress, and in some instances thixotropic behavior. Such high-concentration, nonideal (dirty) suspensions in the resource industries have meant that new rheological methods and techniques have been needed to measure and interpret the basic flow properties. Also, some older empirical techniques have needed to be modified and interpreted in a more fundamental way so that the results could be used in design. This article reviews these techniques and illustrates how the industry itself has motivated their development. Understanding and exploiting this rheology has resulted in dramatic improvement in the waste-disposal strategy for some industries, but many have failed to embrace the available technology. The reasons for this are discussed. The article concludes that a greater positive change in waste-management practice will occur in the future, motivated by several factors, including public perception, tighter regulation, and perhaps even commonsense life cycle accounting.