Emulsion production stability

Photographic Ag halide emulsions are stabilized against the formation of spontaneous fog by incorporation of this product Additive for developing photographic materials... 

Emulsion Adhesives. The most widely used emulsion-based adhesive is that based upon poly(vinyl acetate)—poly(vinyl alcohol) copolymers formed by free-radical polymerization in an emulsion system. Poly(vinyl alcohol) is typically formed by hydrolysis of the poly(vinyl acetate). The properties of the emulsion are derived from the polymer employed in the polymerization as weU as from the system used to emulsify the polymer in water. The emulsion is stabilized by a combination of a surfactant plus a coUoid protection system. The protective coUoids are similar to those used paint (qv) to stabilize latex. For poly(vinyl acetate), the protective coUoids are isolated from natural gums and ceUulosic resins (carboxymethylceUulose or hydroxyethjdceUulose). The hydroHzed polymer may also be used. The physical properties of the poly(vinyl acetate) polymer can be modified by changing the co-monomer used in the polymerization. Any material which is free-radically active and participates in an emulsion polymerization can be employed. Plasticizers (qv), tackifiers, viscosity modifiers, solvents (added to coalesce the emulsion particles), fillers, humectants, and other materials are often added to the adhesive to meet specifications for the intended appHcation. Because the presence of foam in the bond line could decrease performance of the adhesion joint, agents that control the amount of air entrapped in an adhesive bond must be added. Biocides are also necessary many of the materials that are used to stabilize poly(vinyl acetate) emulsions are natural products. Poly(vinyl acetate) adhesives known as "white glue" or "carpenter s glue" are available under a number of different trade names. AppHcations are found mosdy in the area of adhesion to paper and wood (see Vinyl polymers). 

Metal poHshes may contain emulsifiers and thickeners for controlling the consistency and stabilization of abrasive suspensions, and the product form can be soHd, paste, or Hquid. Liquid and paste products can be solvent or emulsion types the market for the latter is growing. Formulas for metal poHshes are Hsted ia Reference 12. A representative Hquid emulsion product may contain 8—25 wt % abrasive, 2—6 wt % surfactant, 0—5 wt % chelating agents, and 0—25 wt % solvent, with the remainder being water. The abrasive content ia an emulsion paste product is greater than that ia a solvent product. 

Product Stability and Emulsion Stability. These properties are not necessarily related, but are both highly prized in the selection of a carrier. The first refers to the storage or shelf stabiUty of the product. Many carrier preparations are not properly balanced, or unsuitable emulsifiers have been used. Upon storing, these products separate in layers, particularly when exposed to temperature changes. 

D Miller, EM Wiener, A Turowski, C Thunig, H Hoffmann. O/W emulsions for cosmetic products stabilized by alkyl phosphates rheology and storage tests. Colloids Surfaces A Physicochem Eng Aspects 152(1-2) 155-160, 1999. 

Consider the following real life example of a process for a specific product P . This product is an oil-in-water emulsion with a droplet size of about 2pm. The emulsion is stabilized by two different emulsifiers, El and E2 . El is a so-called small emulsifier and E2 a so-called big emulsifier. The product developer specifies the levels of the oil, El and E2 and the water phase. 

Possible effects on degradation, emulsion production, or crud stabilization Liquid-solid separation ... 

Another associated issue was the possibility of inactivating the LRES (lym-phoreticuloendothelial system). By analogy with other injectable systems, it could also be deduced that the injectable emulsion system needed to be sterile and apy-rogenic and free of acute or chronic toxicities from components or their associated degradation products. It also followed that the injectable system required to be stable, although how stability was to be determined and, more to the point, measured, has remained an issue to the present day. This is mainly because emulsions are thermodynamically unstable although their stability can be extended by formulation. As a result emulsion products are now available that are submicron in diameter, sterile, and stable for several years after preparation. In major part this has been due to the use of phospholipids as stabilizers and emulsifiers, in particular the mixed products identified as the lecithin of commerce. 

The ingredient composition and manufacturing process are important for the different types of whippable emulsions. In many industrially produced whippable emulsions, functional ingredients, such as food emulsifiers and hydrocolloids are used to improve functionality and product stability. 

Particle size and particle aggregate size distribution is now being used for monitoring product stability and functional properties in a range of food emulsion systems24. 

The properties of the water phase in whippable emulsions are important for product stability. The water phase is influenced by the soluble components of the systems, i.e., sugars, proteins and hydrocolloids. Interfacial hydration may also influence the properties of the water phase, particularly in high-fat systems. 

Some products, like butter and margarine are stabilized by fat crystals. Salad dressings and beverage emulsions are stabilized by other emulsifiers. The stability of non-protein stabilized food emulsions, involving lower molar mass type molecules, tend to be better described by the DLVO theory than are protein-stabilized emulsions. An example of an O/W emulsifier whose emulsions are fairly well described by DLVO theory is sodium stearoyl lactylate [812],... 

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 increasing demand for products with well-defined composition and properties has aroused much interest in elucidating the basic mechanisms behind emulsion production and stabilization under different conditions [39]. 

In reference to the example of the stability of bitumen-in-water emulsions, production samples were obtained from the Alberta Research Coun-... 

Oil and water [oil-in-water (0/W) or water-in-oil (W/0)] emulsions are utilized for the production of nanoparticle dispersions. The colloidal emulsions are stabilized by a film of surfactants and polymers, which interact with the oil and water phases to prevent aggregation and droplet growth. These microemulsions are typically used as templates for the production of nanoparticles and solid lipid nanoparticles (SLN). 

Food products As thickeners, to provide specific rheology, to form gels, to inhibit syneresis, to stabilize emulsions, to stabilize suspensions, to emulsify, to bind/hold water, to form films and coatings, to inhibit crystallization, to improve texture/mouthfeel, as processing aids, as whipping agents, to stabilize foams, as extrusion aids, as binders, to stabilize proteins, to encapsulate, to flocculate... 

The former is directly proportional to the square of the droplet size according to the Stokes-Einstein expression. In spite of the broad droplet size distribution and the changing droplet size with time, measuring the creaming rate can still provide a useful method for determining the relative droplet sizes of different emulsion products. The ultimate emulsion stability is not solely controlled by... 

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