Breakdown of emulsions

The breakdown of emulsions can either be desirable or unwanted. Of course, cosmetic emulsions such as creams or cleansers have to be stable and become useless if separated. On the other hand, in processes such as enhanced oil recovery emulsions may be formed that are considerably stable and a notable effort is necessary for their separation. 

Generally speaking, for a stable emulsion a densely packed surfactant film is necessary at the interfaces of the water and the oil phase in order to reduce the interfacial tension to a minimum. To this end, the solubility of the surfactant must not be too high in both phases since, if it is increased, the interfacial activity is reduced and the stability of an emulsion breaks down. This process either can be undesirable or can be used specifically to separate an emulsion. The removal of surfactant from the interface can, for example, be achieved by raising the temperature. By this measure, the water solubility of ionic surfactants is increased, the water solubility of non-ionic emulsifiers is decreased whereas its solubility in oil increases. Thus, the packing density of the interfacial film is changed and this can result in a destabilisation of the emulsion. The same effect can happen in the presence of electrolyte which decreases the water solubility mainly of ionic surfactants due to the compression of the electric double layer the emulsion is salted out. Also, other processes can remove surfactant from the water-oil interface - for instance a precipitation of anionic surfactant by cationic surfactant or condensing counterions. 

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It has been known for many years that microbial contaminants may effect the spoilage of pharmaceutical products through chemical, ply sical or aesthetic changes in the nature of the product, thereby rendering it unfit for use (see Chapter 18). Active drug constituents may be metabolized to less potent or chemically inactive forms. Physical changes commonly seen are the breakdown of emulsions, visible surface growth on solids and the formahon of slimes, pellicles or sediments in hquids, sometimes... 

The following sections discuss the various instability mechanisms that result in the breakdown of emulsions. Because most of these instability mechanisms are driven by droplet-droplet interactions that occur on the colloidal level, the physical bases of colloidal interactions should be understood as well. Such a detailed discussion is, however, beyond the scope of this unit and interested readers are... 

When the problem is to disrupt Ughtly bonded clusters or agglomerates, a new aspect of fine grinding enters. This may be iUustrated by the breakdown of pigments to incorporate them in liquid vehicles in the making of paints, and the disruption of biological cells to release soluble produces. Purees, food pastes, pulps, and the like are processed by this type of mill. Dispersion is also associated with the formation of emulsions which are basically two-fluid systems. Syrups, sauces, milk, ointments, creams, lotions, and asphalt and water-paint emulsions are in this categoiy. 

Electrical Stability of Emuisions. The electrical stability test indicates the stability of emulsions of water in oil. The emulsion tester consists of a reliable circuit using a source of variable AC current (or DC current in portable units) connected to strip electrodes. The voltage imposed across the electrodes can be increased until a predetermined amount of current flows through the mud emulsion-breakdown point. Relative stability is indicated as the voltage at the breakdown point. 

Use well-designed, specialized polymer dissolution systems wherever possible (such as those from the U.S. Filter, Inc. subsidiary, Strandco ), especially for emulsion polymers, rather than simple dissolving tanks and mixers with propeller-type impellers. This prevents undissolved lumps of polymer (fish-eyes) and the breakdown of polymer chains. Always install a strainer to prevent possible pump clogging. 

In a recycling system, the aqueous discharge effluent from both centrifiiges is returned to the extractors for additional oil recovery, the water being reused. During this extraction process the viscosity of the emulsions increases because peel polysaccharides, mainly pectins, are transported with the emulsion. Enzymatic breakdown of the internal links of the pectin, catalysed by endopolygalacturonase activity, produces an important decrease in the viscosity of the emulsion [16]. In addition, enzymatic treatment removes pectins from the emulsion and contributes to it destabilization [17]. 

Lipoprotein lipase Enzyme located in the capillary endothelium involved in the breakdown of intravenous lipid emulsion particles. 

In 1991, 12.5 million gallons of fire resistant fluids (probably including water-in-oil emulsions) were sold this is the lowest sales volume since 1985 (NPRA 1992). No detailed breakdown of water-in-oil emulsion hydraulic fluids was provided in NPRA (1992). 

Solans et al. [80] studied the effect of shear rate on shear stress, x, for w/o HIPEs of shear rate, the shear stress was seen to rise to a maximum then quickly fall to zero, with time. This was attributed to the breakdown of the emulsion at higher rates of shear. 

Advantages Relatively rapid test that does not rely on the use of an external force to breakdown an emulsion. Common laboratory equipment is used. Small quantities of protein are used. Disadvantages Emulsions must be prepared under standardized conditions. Some studies have found poor correlations between EAI and emulsion stabilly in food systems. 

Storage conditions should accurately reflect the conditions encountered in the actual production/storage process. The primary parameter to control is temperature. If the container is not properly seeded, other parameters such as relative humidity, air pressure, and air composition may affect the rate of emulsion breakdown. 

Figure 3.27 Breakdown mechanisms of emulsions (from top to bottom creaming, coalescence, flocculation and Ostwald ripening).

Apart from microemulsions, all types of emulsions are thermodynamically unstable and their stability is solely a kinetic issue. The relevant timescale can vary between seconds and years. The following mechanisms are responsible for the breakdown of an emulsion. They are depicted schematically in Figure 3.27. 

Klemaszewski, J.L., Haque, Z., Kinsella, J.E. 1989. An electronic imaging system for determining droplet size and dynamic breakdown of protein-stabilized emulsions. J. Food Sci. 54, 440-445. 

Figure 1. Schematic representation of emulsion formation and breakdown. (Adapted from reference 1.)...

Selection of a suitable chemical emulsion breaker and dosage is crucial. A particular demulsifier may be effective and efficient for one emulsion yet entirely unsatisfactory for another. Contemporary demulsifiers are formulated with polymeric chains of ethylene and propylene oxides of alcohol, alkyl phenols, amino compounds, and resinous materials that have hydroxy acceptor groups. Each of these polymers is carefully formulated to yield a molecule with a particular affinity for water. Demulsifier dosage is also important excessive demulsifier addition can inhibit the efficiency of emulsion breakdown. 

Fig. 3 Schematic representation of the various processes of emulsion breakdown.

There are two control rooms. One is near the nitrator house in a control bunker, another is further away in a remote control room at a safe distance. The latter is provided with instruments to start, supervise Redox, pM NG-water emulsion and a device to shut down the unit. Both control rooms are provided with TV sets. Signals between the two houses are both electric and pneumatic, although controls on the nitration unit are only pneumatic. The remote control room is operated in case of emergency and necessity or breakdown of the automatic system. 

One of the main drawbacks to the commercial development of multiple emulsions is their inherent instability. The intention of this paper is to review studies on the stability and mechanism of breakdown of multiple systems and attempts to minimise such instability, for example, by appropriate choice of surfactant, polymerisable surfactants or gelation of the aqueous or oily phases. 

Pancreatic lipase, in the presence of bile salts and coUpase, acts at the oil-water interface of the triglyceride emulsion to produce fatty acids and 2-monoacylglycerols. Cohpase is secreted in pancreatic juice as an inactive proenzyme, which is converted to the active form by trypsin. Other significant enzymes involved in the breakdown of fats within the intestinal lumen are cholesterol ester hydrolase, phospholipase A, and a nonspecific bile salt-activated lipase. 

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