Flocculation behavior

FIGURE 22.2 Flocculation behavior of the smaU-strain modulus at 160°C of uncross-linked solution-based styrene-butadiene rubber (S-SBR) composites of various molar mass with 50 phr N234, as indicated (left) and strain dependence of the annealed samples after 60 min (right). (From Kliippel, M. and Heinrich, G., Kautschuk, Gummi, Kunststoffe, 58, 217, 2005. With permission.)... 

In Fig.7, the effect of the adsorption temperature of HPC in preparing the polymer-coated latices on the flocculation behavior of the system is demonstrated. It was found that both systems show almost the same behavior in flocculation, but evince a fairly different behavior in protection. The HPC-coated latex suspension treated at room temperature flocculated in a 1.2 Mol MgCl2 aqueous... 

Figure 8.8. Schematic illustrating the analogy between colloid flocculation behavior and phase behavior of the stabilizer in bulk solution. As density is lowered, separation of solvent from chains in bulk solution resembles separation of solvent from chains on surfaces, which produces flocculation.

The behavior of neutral brushes in good solvent conditions has been generalized to any solvent quality [218,219]. In 0 solvent, the excluded volume, which is the second virial coefficient, is equal to zero. As a consequence, the thickness L results from the balance between the three-body interaction forces (positive and proportional to c3) and the chain elasticity. In a poor solvent, the chains shrink, and the elasticity term is irrelevant. The determination of L thus results from the equilibrium between the two-body and three-body interaction forces. The expression of L as a function of N, a, d, and the second and third virial coefficients is obtained by the authors, who demonstrate that the brush configuration is preserved in both the 0 and the poor solvent with a linear variation of L with N. The brush thickness continuously decreases as the solvent quality decreases. Experimentally, this can be suitably achieved by varying the temperature. The effect of changing solvent quality on the flocculation behavior of emulsions stabilized by copolymers was discussed by March and Napper [154] (Sec. III.B). Even if the random copolymers used in this study are not expected to form brushes, it was clear that flocculation was observed in 0 solvent conditions while it was suppressed in good solvent conditions. 

Starch-induced flocculation of 1% (w/w) kaolin suspensions and the adsorption of NaCMC were investigated by Jamstrom et al., where the kaolin was partly pretreated with sodium polyacrylate of low molecular weight (PAA) [22], In all flocculation experiments the kaolin suspension as well as the starch solution were adjusted to pH 7.5. The flocculation behavior of the PAA-treated suspension indicated that depletion flocculation is a very likely flocculation mechanism. When a hydrophobically modified starch was added, no flocculation occurred, and no adsorption of the modified starch on the kaolin particles could be detected. It is reasonable that water is a less good solvent for the hydrophobically modified starch and thus may cause the impossibility of depletion flocculation. On the other hand, a dispersing... 

L Nabzar, E Pefferkorn, R Varoqui. Polyacrylamide-sodium kaolinite interaction flocculation behavior of polymer clay suspensions. J Coll Interf Sci 102 380-388, 1984. 

The effects of molecular weights and charge characteristics of flocculants on the flocculation behavior of particles of different sizes are summarized in Table 5.31. 

Morgan, J. T. Birkner, F. B. Flocculation Behavior of Dilute Clay-Polymer Systems, Progress Report WP 00942-02, U.S. Public Health Service, Sept. 1966. 

One of the possible ways to achieve this flocculation behavior is using inorganic salts in solution. By changing their concentration, the potential, as well as the double-layer thickness, will in gen al be modifled. As a consequence, the potential energy of interaction between the panicles can change from that of an essentially stable system to that of a rapidly coagulating suspension. Under certain conditions, illustrated in Fig. 7, a secondary minimum in the potential energy vs. distance curve may show up this ideal condition would correspond, as mentioned above, to the open flocculi that can be easily redi.sper.sed and hence are suitable for oral administration. 

Figure 6. Schematic illustrating the analogy between colloid flocculation behavior and behavior of the stabilizer in bulk solution.

Research in this area shows great potential. Over the past 30 years, dual systems have been applied mainly in the paper industry. The applicatimi of PECs, described as particle-forming flocculants, provides new possibilities in solid-liquid separation processes. For an effective system, the application parameters have to be optimized (e.g. polymer type, cmicentratiOTi, charge, molecular weight). Therefore, direct and efficient methods for the characterization of the flocculation behavior (sedimentation velocity, packing density of the sludge, particle size distribution) are necessary and will be described. 

One example of a very special dual-component polymeric flocculant is poly (ethylene oxide) (PEO) and carboxylated phenolic resin (CPR), usually referred to as a cofactor. It has been shown that this dual flocculant can induce a richness of flocculation behavior depending on the concentration of the two components [40,41]. Flocculation, deflocculation, and reflocculation of cellulose particles were studied for various CPR PEO ratios. It was found that reflocculation is a strong function of this ratio. For low ratios, no reflocculation occurs after a few cycles, whereas for high ratios very limited flocculation and reflocculation occurs. 

Nystrom et al. [92, 93] correlated the observed flocculation behavior of calcium carbonate, induced by mixtures of cationic starch and anionic poly(sodium acrylate) (NaPA) at various electrolyte concentrations, with the complex properties. A strong correlation exists between the properties of the PEL mixture, primarily the amount of complexes formed, and the flocculation behavior. Several mechanisms are involved in this flocculation process induced by the two polymers. However, interparticle bridging by the PECs and charge neutralization induced by the deposition of the complexes were found to be the main reasons for the enhanced flocculation. 

The flocculation mechanism ofZ. mobilis ZM401 has not been understood so far. However, research has shown that the enzyme cellulase could effectively defloc-culate the cell floes of ZM401, and enhanced cellulose production facilitated more stable flocculent behavior in ZM401 [33]. This indicates that the self-flocculation of ZM401 cells might be attributed to the enhanced cellulose biosynthesis in this Z. mobilis mutant. 

Esumi et al [68] used dispersions of a-alumina as well to study the interaction between anionic fluorocarbon and hydrocarbon surfactants. The anionic fluorocarbon surfactants used were LiFOS and NFIOO, the anionic hydrocarbon surfactants were SDS and LiDS, and the nonionic surfactant was NP7.5. Like the flocculation behavior of iron hydroxide, a low concentration of an anionic surfactant precipitates alumina. A further addition of a surfactant, different from the first one, forms mixed bilayers and redisperses alumina. Measurements of zeta potentials, the size of adlayers, and the amounts of adsorbed surfactants indicated that mixed bilayers consisting of anionic hydrocarbon-nonionic hydrocarbon surfactants or anionic fluorocarbon-nonionic hydrocarbon surfactants are formed preferentially to hydrocarbon-fluorocarbon surfactant bilayers. 

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