Emulsion systems, incorporation

In emulsions, partitioning of the incorporated preservative can occur between the aqueous and the oil phase. A lipophilic preservative may pass into the oil phase so that a significant portion is removed from the aqueous phase. Since it is the latter in which microorganisms tend to grow, the use of water-soluble preservatives can be more effective, especially for O/W emulsions. For most emulsion systems, the esters of p-hydroxybenzoic acid (parabens) appear to be the most satisfactory. Since microorganisms can also reside within the oil phase, it is further recommended that a pair of preservatives having different oil and water solubilities be used in order to ensure appropriate concentrations in both phases. 

Option 1 system incorporates the emulsion breaking process followed by surface skimming (gravity separation is adequate if only free oils are present). 

In order to circumvent this sensitivity limitation, the San Jose researchers sought to design resist materials that incorporate chemical amplification of the sort that characterizes the silver halide photographic emulsion system. In these systems a single photo event initiates a cascade of subsequent chemical reactions that ultimately result in the intended function. 

Kawakami, S., Yamashita, R, and Hashida, M. (2000) Disposition characteristics of emulsions and incorporated drugs after systemic or local injectioAdv. Drug Del. Rev., 45 77-88. 

Commercial process for the production of PCTFE is essentially polymerization initiated by free radicals at moderate temperatures and pressures in an aqueous system at low temperatures and moderate pressures. It is reported that it is possible to polymerize CTEE in bulk, solution, suspension, and emulsion. According to some reports the emulsion system produces the most stable polymer [65]. The tendency of PCTFE to become brittle during use can be reduced by incorporating a small amount (less than 5%) of vinylidene fluoride (VDF) during the polymerization process [67]. 

An area of interest at that time was the incorporation of colloidal silica into emulsion systems. Typical emulsions included floor waxes or rubber latices. Conventional wax compositions ordinarily included certain extenders or modifiers in the wax dispersions. These may comprise wax-soluble or water-dispersible resins (natural or synthetic). These formulations can produce coatings with a pleasing appearance however, many lack slip resistance. The incorporation of colloidal silica into the formulation produces coatings that prevent slipping. 

The dry adsorbed emulsions are easy to prepare industrially (without any u.se of solvents) and their different particle sizes convenient to handle. Particles of dry adsorbed emulsions are incorporated in hard gelatin capsules or tablets to obtain a sustained drug delivery system for oral route that is well accepted by patients. The sustained relea.se effect depends mainly on the particle size of (he form, on the composition of the primary emulsion oil phase, and on the process of manufacturing, The adsorbent and drug nature and physicochemical properties are al.so important in the drug release profile. 

Features Stable aq. emulsion easily incorporated by simple stirring in water-based UV-curable systems nonvolatile fast cure response optimum absorp. 210-330 nm... 

Surface-Active Materials. The active defoamer components are necessarily surface active materials, but this ancillary category covers the surfactants that are often incorporated in the formulation for other effects such as emulsification or to enhance dispersion. Emulsifiers are essential in the common oil-in-water emulsion systems, but they are also required where mixtures of active liquid components are used. For example, specialized oil-in-oil emulsifiers are needed in defoamers based on silicone/polyether mixtures, oil-in-water emulsifiers are incorporated in some defoamers even when the final product contains no water. This is to promote emulsification (self-emulsifiable) or dispersion into aqueous foaming systems. These additives increase the speed of foam decay by promoting rapid dispersion of the defoamer throughout the foaming media. Examples of emulsifying agents used in defoamer compositions are fatty acid esters and metallic soaps of fatty acids fatty alcohols and sulfonates, sulfates, and sulfosuccinates sorbi-tan esters ethoxylated products such as ethoxylated octyl or nonylphenols and silicone-polyether copolymers. 

Caprylic acid is effective against bacteria and fungi, optimum pH range < 6. Due to its limited water solubility it may be insufficiently active to protect the water phase of emulsion systems against microbial proliferation. A main application field for caprylic acid is the incorporation into cheese wrappers as an antimicrobial active ingredient. Caprylic acid may also be used as a flavouring adiuvant (Doores, 1993). Worthy on note is that caprylic acid exhibits insecticidal activity, too. 

Size Microreactor systems incorporate structures for the directed transport or containment of gases or fluids that have a dimensional property in at least one direction usually measured in micrometers, sometimes up to 1 mm. These structures may comprise microscale ducts (e.g., channels and slots) and pores, larger features (e.g., parallel plates) that cause fluid to flow in thin films, and others that cause fluid to flow in microscale discontinuous multiphase flow (e.g., bubbles and emulsions). More specific details of these types of structure are explained in Chapters 9 and 10. In addition, small containment structures such as microwells have been fabricated in an analogous format to traditional microtiter plates, rendering potential compatibility with existing robotic handling... 

Interfacial polymerization techniques can be used to prepare robust microcapsules (about 4 pm) that have selectively incorporated functionality such as catalytic groups in their liquid-core domains. The synthesis of these particles is achieved via an oil-in-oil emulsion in combination with interfacial polymerization methods and allows for the encapsulation of substrates not compatible with water-in-oil or oil-in-water emulsion systems (Kobalija and McQuade, 2006). Often these capsules have polyurea shells that can be formed from w/o emulsions containing reactive polyols and isocyanates. This has been very elegantly demonstrated by McQuade and coworkers for the DMAP-catalyzed acylation transformation of an alcohol within the protected environment of polyurea microcapsules formed from reaction of a polyisocyanate and a poly(vinyl alcohol) in the presence of an amine catalyst (Price et ah, 2006 Poe et al, 2007). 

Alkoxysilanes can also act as oil droplets. Hollow silica microspheres of diameters 0.3-65 pm were prepared in a CTAB-stabilized emulsion system consisting of water and the mfacture of TEOS and aminopropyltriethoxysilane (10 mol%) as the oil phase [18]. Organo-functionalization of the microspheres was achieved by replacing TEOS with organotriethoxysilane, and encapsulation of TEOS-soluble additives within the silica shdls was demonstrated by incorporation into the ethoxysilane droplets. 

Ascorbic acid (vitamin C) has been incorporated in both W/O/W and O/ W/O multiple-emulsions systems (Silva et al., 1997 Gallarate et al., 1999 Farahmand et al., 2006). In the first system, vitamin C was dissolved in the inner aqueous phase of a W/O/W multiple emulsion. In this case, improved protection against oxidation was reported when compared with O/W microemulsion, O/W and W/O emulsions, both at 45°C and 20 0. Incorporating vitamin C in the intermediate aqueous phase of an O/W/O multiple emulsion improved the occlusive properties, the acceptability and durability on skin. 

Traditionally, hydroxy ethyl cellulose was the most commonly used thickener ( viscosity increaser ) for emulsion systems. The cost was low and delayed action grades were easy to incorporate. Very small additions can produce large changes in viscosity. However, the rheology of these solutions is far from Newtonian and can lead to thixotropic final products. Solvents also have a marked effect on the viscosity of hydroxy ethyl cellulose. 

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