Emulsions mechanical stabilization

The quality of the water used in emulsion polymerization affects the manufacture of ESBR. Water hardness and other ionic content can directly affect the chemical and mechanical stability of the polymer emulsion (latex). Solution polymerization can use various solvents, primarily aliphatic and aromatic hydrocarbons, SSBR polymerization depends on recovery and reuse of the solvent for economical operation as well as operation under the air-quality permitting of the local, state, and federal mandates involved,... 

Understanding the relationship between the composition of a mixture and its properties is fundamental to the development of formulated products. In the pesticide industry, formulation chemists seek to translate such an understanding into products that meet criteria established for properties such as suspensibility, emulsibility, storage stability, compatibility, and most importantly, biological activity. The preferable way to acquire the necessary knowledge is to deduce the properties of mixtures in terms of mechanisms that are operative at the microscopic level. However, mixtures are extremely complex systems and the available theory is usually insufficient for developing useful theoretical models. For example, we are unable quantitatively to predict, on the basis of molecular theory, the suspensibility of a wettable powder from a knowledge of its composition. 

The object of this study was to clarify some aspects of the mechanism of shear-induced flocculation in colloidal dispersions. Vinyl chloride homopolymer and copolymer latices were prepared by emulsion polymerization using sodium dodecyl sulphate as emulsifier. Agglomeration behavior in these latices was studied by measuring the mechanical stability using a high speed stirring test. The latex particle size was measured by an analytical centrifuge. Molecular areas of emulsifier in the saturated adsorption layer at the surface of homopolymer and copolymer latex particles were estimated from adsorption titration data. 

Copolymers 59 [181] and terpolymers 60 [182] were synthesized by micellar copolymerization and characterized with respect to their molecular and solution properties. The subject of further investigations was the interaction with low molecular weight surfactants [181,183]. Another interesting use was made of hydrophobized sulfopropylammonio monomers as surface-active monomers (or surfmers ) [184]. Their use in emulsifler-free emulsion polymerizations [185] reduced the water uptake and improved the mechanical stability of the resulting filmed latexes. 

Milkfat is present in milk or cream as part of a stable oil-in-water emulsion. The emulsion is stabilized as a result of the protein and phosphohpid-rich milkfat globule membrane (MFGM) surrounding the milkfat. During AMF manufacmre, the aim is to break the emulsion and to separate out all of the nonfat solids and water (Figure 18). To achieve this, the MFGM must first be dismpted mechanically or... 

Broad Influence on Stability. In general, when electrical surface charge is an important determinant of stability, it is easier to formulate a very stable OAV emulsion than a W/O emulsion because the electric double-layer thickness is much greater in water than in oil. (This condition is sometimes incorrectly stated in terms of greater charge being present on droplets in an OAV emulsion). This is not to say that W/O emulsions cannot be stabilized, however. Many reasonably stable oil-field W/O emulsions are stabilized by another mechanism the protective action of viscoelastic, possibly rigid, films formed on the droplets by macromolecules or solid particles. 

Surface-active agents. Surface-active agents such as emulsifiers and surfactants play a very significant role in the stability of emulsions. They greatly extend the time of coalescence, and thus they stabilize the emulsions. Mechanisms by which the surface-active agents stabilize the emulsion are discussed in detail by Becher (19) and Coskuner 14). They form mechanically strong films at the oil-water interface that act as barriers to coalescence. The emulsion droplets are sterically stabilized by the asphaltene and resin fractions of the crude oil, and these can reduce interfacial tension in some systems even at very low concentrations (i7, 20). In situ emulsifiers are formed from the asphaltic and resinous materials found in crude oils combined with ions in the brine and insoluble dispersed fines that exist in the oil-brine system. Certain oil-soluble organic acids such as naphthenic, fatty, and aromatic acids contribute to emulsification 21). 

For maximum mechanical stability, the interfacial film resulting from the adsorbed surfactants should be condensed, with strong lateral intermolecular forces, and should exhibit high film elasticity. The liquid film between two colliding droplets in an emulsion is similar to the liquid lamella between two adjacent air sacs in a foam (Chapter 7) and shows film elasticity for the same reasons (Gibbs and Marangoni effects). 

More often however, water in crude petroleum is present in its dispersed form, emulsion of water in oil. There are two versions of this emulsion mechanical non-stabilized and stabilized by interfacial-active substances. This distinction for emulsions is essential for petroleum drying. Water from non-stabilized emul-... 

The mechanical stability of polymers was related to the polymer s conformation in some of the earlier drag-reduction studies. Above a critical stress, degradation was faster the more contracted and entangled the polymer s conformation (5-7). In petroleum applications the mechanical instability of synthetic relative to carbohydrate polymers was well-recognized. The relative stability problems (possibly related to DUEVs (8)) encountered in the use of high molecular weight hydrolyzed poly(acrylamide) (HPAM) led to the development of an inverse-emulsion polymerization technique (9). (Current research directions using this technique are discussed in Chapter 9.)... 

The coalescence rate, i.e. formation of larger droplets after collision of two droplets, depends on the number of collisions and on the properties of the adsorption layers. For dilute emulsions, as well as emulsions having V2 = 0.3—0.74, coalescence is the main process leading to the disturbance of their aggregative stability. Hence, prerequisite for the production of appreciable volumes of any type of emulsions suitable for practical application is provision of their coalescence stability. In case of o/w emulsions, maximum stability against coalescence is achieved through the formation, on the surface of the disperse phase particles, of structured adsorption layers, a structure-mechanical barrier defined by Rehbinder [8]. Such layers are... 

The stability improvement of Ti02 suspensions is important not only for water-based paints, but also for paints based on non-polar or low-polar solvents. It is shown in [208] that Ti02 powders modified with an anionic surfactant, e.g. sodium dodecyl sulphate, are dispersed to smaller sizes, and their sedimentation stability increases. The production of water-alkyd emulsions is inhibited due to low mechanical stability. These emulsions can easily break when exposed to shear forces such as those produced by pumps, and when intensively agitated during dispersion. [209] demonstrates that most stable emulsions can be obtained with alkyds showing high acid numbers, as well as with highly polymerised alkyds of low viscosities. 

The behavior of proteins at interfaces influences the formation of foams and emulsions (32). Stabilization of foams and emulsions depends, to a great extent, on the formation, rheological, and mechanical properties of the interfacial film ( ). Factors which ensure optimum film properties in simple systems may retard film formation or cause destabilization in foams or emulsions (3 ) for example, many rheological properties of films are maximum in the isoelectric pH range of specific proteins, yet most proteins have minimum solubility in this pH range (34). Thus, environmental and processing factors which... 

For use with high-speed applicators, high shear cone and plate viscometer results may be quoted as secondary information. Many poly(vinyl alcohol)-stabilized products are comparatively insensitive to shear and give broadly similar results with different types of viscometer. This behavior under shear is known as Newtonian and is a feature, inter alia, of large particles with a narrow particle size distribution. High shear viscosity testing also indicates if there is sufficient mechanical stability to allow application by knife or roller, although this is not usually a problem with colloid-stabilized emulsion polymers and adhesives. 

Typical enulsifiers used in emulsion polymerization of VC are anirmic emulsifiers like sodium alkyl sulfonates, sodium diaUcyl sulfosucdnates, fatty acid soaps and sodium ethoxy sulfates. Neutral emulsifiers like alltyl phenol ethoxylates and fatty acid ethoxylates are often added during after polymerization in Oder b> increase latex stability. The emulsifiers are not only chosen for control of the particle formation and latex stability during polymerization, but for a number of other reasons like mechanical stability, reactor wall build-up, plastisol formation, heat and colour stability and water resistance of the final product [1]. 

It is well recognized that these emulsions are stabilized by means of an interplay between different heavy components, organic and inorganic particles, respectively. Heavy components cover asphaltenes, resins, etc. In a depressurized anhydrous crude oil the asphaltenes are normally in a particulate form. The role of the resins (and lighter polar components) is to stabilize the asphaltene dispersion (suspension) by adsorption mechanisms. Owing to this strong interaction the asphaltene particles are prevented... 

Mechanical stabilization is a process where interfacial components act as particles, creating a mechanically stable film on the surface of the droplets. This film encapsulates the droplets and, due to its immobility and low solubility in both water and oil, creates a very stable emulsion. Asphaltenes, resins, wax particles, minerals, and clay are compounds believed to enhance the formation of mechanically stable films. 

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