Gudrun Petzold

Higher efficiency in the flocculation of clay suspensions by using combinations of oppositely charged polyelectrolytes

Abstract Dual systems—the highly charged polycation poly(diallyll-dimethyl-ammoniumchloride) (PDADMAC) in combination with different high molecular weight polyanions of the polyacrylamide type—were tested as flocculants for clay suspensions and natural waste waters from gravel pits. The flocculant performance was characterised by measuring the sedimentation behaviour as well as the residual turbidities and the extent of polymer adsorption. Whereas the molecular weight of the high molecular weight polycation is of lower influence, the removel of suspended particles is greatly affected by the molecular weight of the polyanion. Our experiments showed that degradation of the very high molecular weight polyanions leads to higher turbidity of the supernatant. The order of addition of the two polyelectrolytes influences the flocculation mechanism. Most effective is the addition of polycation followed by the polyanion. So a combination of patching and bridging is obtained.

The use of oppositely charged polyelectrolytes as flocculants and retention aids

Abstract New results for flocculation of cellulose-clay mixtures with a so-called dual system, consisting of the polycation poly(dimethyldiallylammonium chloride), PDMDAAC, and different polyanions are presented. The flocculation behaviour was investigated by different procedures: polyelectrolyte titration, dewatering test, and measuring the residual turbidity. It should be pointed out that the flocculation mechanism depends on the molecular weight of the polyanion used. In the first case, when the molecular weight of the polyanionic compound is relatively low, the complexation between the polycation and the polyanion is said to be the mechanism and the ratio of anionic to cationic charges (n−:n+) is of crucial importance. Using a very high molecular weight polyanion (⪢ 1 million) as one component of the dual system, the mechanism of reaction consists of bridging and patch effects.

Polyelectrolyte Complexes in Flocculation Applications

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 suspension 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.

The interaction between polyelectrolyte complexes made from poly(dimethyldiallylammonium chloride) (PDMDAAC) and poly(maleic acid-co-α-methylstyrene) (P(MS-α-MeSty)) and cellulosic materials

Abstract The interaction between the oppositely charged polyelectrolytes poly(dimethyldiallylammonium chloride) (PDMDAAC) and poly(maleic acid-co-α-methylstyrene) (P(MS-α-MeSty)) in the presence of cellulose or a mixture of cellulose and clay, respectively, has been investigated. The application of different methods allowed the characterization of flocculation and surface modification. It has been found for step-by-step addition that the flocculation behaviour of this two-component system (dual system) depends on the molar ratio of the two polymers used and also on the concentration of polycation. Only at a certain concentration of PDMDAAC does the two component system lead to a considerable improvement in the flocculation behaviour and in surface modification, as compared to a pure polycation. The addition of a premixed polyelectrolyte complex has also been found to be a successful method. However, the mechanism of flocculation is supposed to be different for complexes with different molar ratios.

Application Relevant Characterization of Aqueous Silica Nanodispersions

This work describes the application relevant characterization of eight commercially available silica powders dependent on dispersing procedure using different instruments: photon correlation spectroscopy, nitrogen adsorption, and particle charge detector. The particle size of silica was found to be different in dispersion from that of all types of fumed silica, where, after proper dispersion, the measured average particle size is similar and much higher than the primary particle size. The different properties of these two silica types will be discussed.

The interaction between oppositely charged polyelectrolytes in the presence of solid surfaces

Abstract The interaction between the oppositely charged polyelectrolytes poly(dimethyldiallylammonium chloride) (PDMDAAC) and poly(maleic acid-co-α-methylstyrene) (P(MS-α-MeSty)) in the presence of inorganic fine particles such as clay, silicic acid and glass pearls has been investigated. In experiments involving only adsorption of PDMDAAC the driving forces are electrostatic attractions between the anionic particles and the polycation. The amount of adsorbed PDMDAAC necessary for changing the surface charge of the substrates from negative to positive increased with increasing specific surface area. The adsorption of PDMDAAC and P(MS-α-MeSty) from their mixed solutions on to the inorganic fine particles showed a synergistic effect with respect to the amount of cationic surface charge. This effect increased with the surface charge density of the solid particles. The interaction of P(MS-α-MeSty) with preadsorbed PDMDAAC led to a change in the polarity of the modified particles and did not show a synergistic effect. The obvious difference between the adsorption from the mixed solutions and sequential adsorption is discussed in terms of the configuration of adsorbed polyelectrolyte complex particles formed in the solution or at the solid/liquid interface.

Polyelectrolyte-surfactant complexes and their influence on the wettability of different polymer surfaces

A novel method to modify the wettability of polymer surfaces is presented. It was found that the surface properties of polymers with different surface-free energies—polyamide 6.6, polypropylene, polyethylene and polystyrene—can be easily changed by a simple modification with premixed polyelectrolyte-surfactant complexes (PSCs). The modification effect can be significantly affected by the complex properties which are influenced by the type of surfactant and polyanion and their charge ratio in a mixture. Complexes having positive charge and low surface tension are most effective. All the complexes investigated show an interaction with polymer surfaces; however, the most effective modification was obtained with hydrophobic substrates such as polypropylene and polystyrene. In contrast to modification with the ‘pure surfactant’, the modification with PSC is persistent also after rinsing.

Investigation of the Charge Behavior of PAA Copolymers by Means of Polyelectrolyte Titration

Simona Schwarz, Christine Steinbach, Dana Schwarz, Gudrun Petzold, Evgenia Romanova, Marina Oelmann Leibniz-Institut für Polymerforschung Dresden e.V. Hohe Straße 6, 01069, Dresden, Germany simsch@ipfdd.de, steinbach@ipfdd.de, petzold@ipfdd.de, romanova@ipfdd.de, oelmann@ipfdd.de Charles University in Prague, Faculty of Science, Department of Organic Chemistry Hlavova 2030/8, 128 43, Prague, Czech Republic