Flocculation polycations

Aggregates like polyelectrolyte complexes having positive charges and hydrophobic domains show a broader optimum flocculation concentration range and are considered as new reactive nanoparticles [11-14], Thus, polycations with hydrophobic functionalities represent an interesting class of water-soluble associating polyelectrolytes relevant for controlled stabilization/flocculation of dispersions in numerous industrial applications. 

The absolute value of the zeta potential decreases until a plateau is reached at a certain polyanion concentration. A contrary effect is obtained in the case of adding a polycation. A partial stabilization of the kaolin particles can be realized due to an adsorption of anionic charged macromolecules at the edges of the kaolin platelets. By adding a polycation to the kaolin dispersion, an adsorption at the negative basal surface becomes possible, and the iep of the particles is reached very quickly at low PEI concentrations. A further addition of PEI leads to an increase of the zeta potential while flocculation was observed. This is because the adsorption of cationic polymer can cause a face-to-face association that can generate polymer-kaolin complexes. 

The commercial polymers have molecular weights of up to 100,000 g/mol and ratios of primary-.secondary tertiary amino groups of 1 2 1. They are used as adhesives (e.g., bonding polyester cord to rubber), paper additives, etc. Quaternized poly(ethylene imines) form water-soluble polycations and are used as flocculants in the processing of tap water. 

Latex coating. The first objective was to cover the latex with the polycations without coagulation. Cationic surfactants as well as polycations are normally used as titrants for the determination of the charge density of anionically stabilized latexes (4). In an impropriate range of concentration, the point of charge compensation is indicated by clearly pronounced flocculation. 

Abstract This review concentrates on the interactions between oppositely charged polyelectrolytes and on the formation of complexes, which can be used for different applications such as paper retention or water treatment. Three different possibilities for the appearance of polyelectrolyte complexes (PECs) in flocculation applications are described. Starting with the classical dual system (step-by-step addition of polycation and polyanion to a negatively charged suspensimi of fibers or particles), the interaction between a soluble polyanion (such as anionic trash) with polycation is described as well as the formation of well-defined pre-mixed PECs and their application as flocculants. 

Fig. 6 Different types of interaction between PC and PA in the presence of particles, depending on the amount of PC and the order of addition (a) low amount of polycation, (b) higher amount of PC (than in a), formation of PEC as an additional flocculant, (c) dosage of PC and PA at the same time...

Because the separation problems have become more and more complex, new principles of flocculation must be used to meet all requirements, such as the removal of heavy metals, dyes, or natural colloids. Instead of monoflocculation with one polycation, pre-mixed PECs (made from PC and PA), which are effective flocculants due to their size and structure, are used. Because hydrophobic interactions are of growing importance for the removal of hydrophobic substances such as oil, it is necessary to introduce hydrophobic parts into the flocculants or, alternatively, to use pre-mixed PSCs. 

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