Abstract
Flocculation of precipitated calcium carbonate (PCC) was monitored using light diffraction spectroscopy (LDS). Four cationic polyacrylamides of high molar mass and with different degrees of branching, all copolymers of acrylamide (AM) and acryloyloxyethyltrimethyl ammonium chloride (Q9), were tested. LDS supplied information about the kinetic curves for flocs growth and also for the flocs structure evolution. Flocculation kinetics, flocs size and structure, flocs resistance and reflocculation capacity could be correlated with the degree of branching of the polyelectrolytes (PEL). Furthermore, PEL with different degrees of branching corresponded to different values for the intrinsic viscosity, indicating differences in the polymer conformation, which explained well the performance differences in flocculation.
Highlights
Polyelectrolytes (PEL) are widely used to achieve efficient solid-liquid separation in many industries [1,2,3,4]
If molar mass is high and the charge density is low, the polymer adsorbs on the particle surface in such a way that tails and loops are extended far beyond the electric double layer of the particle and can interact with the polymer adsorbed on other particles—in this case the flocculation process is dominated by bridging bonds [3,7]
When the charge density is high, the bridging capability is reduced because there is a tendency for the polymer chains to adopt a flatter conformation on the particle surface, which results in the formation of cationic patches that attract the polymer free oppositely charged surfaces of other particles [7]
Summary
Polyelectrolytes (PEL) are widely used to achieve efficient solid-liquid separation in many industries [1,2,3,4]. In the case of papermaking, flocculation is the most important phenomena of the Polymers 2011, 3 wet-end stage since it affects process efficiency (e.g., retention, drainage and runnability) and the quality of the final product (e.g., formation, strength and porosity) [5]. The importance of each process depends on the flocculant characteristics, like chain architecture, molar mass, charge density; on the characteristics of the suspended particles, like size and surface charge; on the characteristics of the suspending medium, like pH, conductivity and ionic strength; and, on the PEL concentration, contact time and turbulence intensity, among others [2,6,7]. Studies have shown that the degree of branching of the polymer affects the flocculation kinetics and the aggregates properties [8]
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