Emulsions problems associated with

In order to be economically viable, a continuous emulsion polymerization process must be able to produce a latex which satisfies application requirements at high rates without frequent disruptions. Since most latex products are developed in batch equipment, the problems associated with converting to continuous systems can be significant. Making such a change requires an understanding of the differences between batch and continuous reactors and how these differences influence product properties and reactor performance. 

There may be problems associated with phase separation due to the formation of emulsion (see Basic Protocol 2). Addition of a salt solution (KC1 or NaCl) and further standing in a cold room is recommended. 

This book focuses on emulsions, foams, and suspensions their fundamentals and applications. The variety of systems represented or suggested by Tables 1.1 and 1.2 underscores the fact that the problems associated with colloids are usually interdisciplinary in nature and that a broad scientific base is required to understand them completely. A wealth of literature exists on the topic of colloidal dispersions, including a range of basic colloid reference texts [12-28], dictionaries [9-11,29], and treatises on the myriad of applied aspects, of which only a few are cited here [1-5,30-36], The widespread importance of emulsions, foams, and suspensions in particular, and scientific interest in their formation, stability and properties, have precipitated a wealth of specialized publications dedicated to each of emulsions [37-42], foams [43-47], and suspensions [48-51],... 

The ring-opening reaction can be performed either as a bulk polymerization, or in solution, emulsion, or dispersion [15,16]. A catalyst or initiator is necessary to start the polymerization. Under rather mild conditions, high-molecular weight aliphatic polyesters of low polydispersity can be prepared in short periods of time. Problems associated with condensation polymerization, such as the need for exact stoichiometry, high reaction temperatures, and the removal of low molecular weight by-products (e.g., water) are excluded in ROP [17]. 

Continuons emulsion polymerization is one of the few chemical processes in which major design considerations require the use of dynamic or unsteady-state models of the process. This need arises because of important problems associated with sustained oscillations or limit cycles in conversion, particle number and size, and molecular weight. These oscillations can occur in almost all commercial continuous emulsion polymerization processes such as styrene (Brooks et cl., 1978), styrene-butadiene and vinyl acetate (Greene et cl., 1976 Kiparissides et cl., 1980a), methyl methacrylate, and chloropene. In addition to the undesirable variations in the polymer and particle properties that will occur, these oscillations can lead to emulsifier concentrations too low to cover adequately the polymer particles, with the result that excessive agglomeration and fouling can occur. Furthermore, excursions to high conversions in polymer like vinyl acetate... 

While analytical derivatizations are an effective way for extracting compounds, these often require additional steps in the analytical procedure and can introduce side products that may interfere with the analysis. Solid phase extraction has provided an alternative method to this process. The advantage of solid phase extraction is that the reagents, derivatives, and side products are maintained on the solid phase. As needed, these derivatives and side products can be selectively eluted after the desired derivative has been formed on the column. In addition, this method can eliminate potential problems associated with emulsion formulation that may occur with liquid-liquid extraction of compounds from the biological matrix. Finally, solid phase extraction is easily amenable to automation with other analytical detection methods such as gas and liquid chromatography. The phases used in solid phase extraction are the standard ones employed in other extraction methods. ... 

This section discnsses the problems associated with ASP, including chromatographic separation, precipitation, scaling, formation damage, and the problems caused by produced emulsion. 

One of the main problems associated with developing a parenteral or any other solution formulation of a compound is its aqueous solubility. For poorly soluble drug candidates, there are several strategies for enhancing their solubility. These include pH manipulation, cosolvents, surfactants, emulsion formation and complexing agents. More sophisticated delivery systems, e.g., liposomes, can also be used in this way. 

Invert emulsion drilling fluids are commonly selected for their temperature stability and their ability to prevent the wellbore stability problems associated with the hydration of clays in shale formations. The thermodynamic activity aw of the water in the aqueous (dispersed) phase is controlled by the addition of a salt (usually calcium chloride) to ensure that it is equal to or less than the activity of the water in the drilled shale formations. The emulsified layer around the water droplets is claimed to act as a semipermeable membrane that allows the transport of water into and out of the shale but not the transport of ions (61). When the activities (or, more strictly, the chemical potentials) of the water in the shale and invert emulsion are equal, then no net transport of water into or out of the shale occurs (i.e., the drilling fluid does not hydrate or dehydrate the shale). This equality of water activity has lead to the development of so-called balanced activity oil-based drilling fluids. 

The high content of nucleic acid in yeast is a potential problem associated with the consumption of large amounts of yeast nucleopro-tein in foods. Phosphorylation is one of the methods used for reducing nucleic acid of yeast proteins (Table 2) [67]. Huang and Kinsella [68] reported the effective removal of nucleic acid from yeast proteins by POCl3-phosphorylation. The phosphorylated protein showed improvement in emulsifying activity and emulsion stability, and produced stable but weak foams at neutral pH. The authors also noted that the in vitro digestibility of yeast protein was not affected by phosphorylation as reported for casein [60] and soy protein [65]. 

The major problem associated with ELMs is emulsion stability. 

This short discussion of problems associated with stabilizing dispersions of PVAc and its copolymers leads to the conclusion that the hydrophilic nature of VAc make placement of stabilizing species (surfactant, charge, hydrated layer, etc.) difficult without incurring additional problems (decrease in rate of polymerization, increase in the concentration of water-soluble oligomers, increase in viscosity, etc.). As a result, a combination of approaches is often used in commercial latex production. The need for better surfactants, especially reactive surfactants, for the emulsion polymerization of vinyl monomers is still evident... 

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