Thickeners multiple emulsions

Thickeners and other additives In some cases a gel coating for the multiple emulsion drops may be beneficial, for example polymethacryhc acid or carboxymethyl cellulose. Gels in the outside continuous phase for a W/O/W multiple emulsion may be produced using xanthan gum (Keltrol or Rhodopol), Carbopol or alginates. 

Several examples of W/O emulsions and W/O/W multiple emulsions based on the block copolymer of PHS-PEO-PHS, have been produced. As an illustration, a typical formulation of W/O/W multiple emulsion is described below, using two different thickeners, namely Keltrol (xanthan gum from Kelco) and Carbopol 980 (a crosshnked polyacrylate gel produced by BF Goodrich). These thickeners were added to reduce creaming of the multiple emulsion. A two-step process was used in both cases. 

The above multiple emulsion was prepared under the same conditions except that Carbopol 980 was used as a thickener (gel). In this case, no MgS04 was added as the carbopol gel was affected by electrolytes. The aqueous PEF127 polymeric surfactant solution was prepared by dissolving 2g of the polymer in 23 g water ... 

As discussed before (2), multiple emulsions (w/o/w or o/w/o) are ideal systems for application in personal care products for the following reasons. First, one can dissolve ingredients in three different compartments. For example with w/o/w multiple emulsions, one can incorporate two different water-soluble additives (proteins, enzymes, and vitamins) and an insoluble ingredient (e.g., perfume). Second, they can be applied for sustained release by control of the breakdown process that occurs on application. Third, they allow one to produce the same cream consistency required for many cosmetics, e.g., by incorporation of a thickener or gelling agent in the outer continuous phase. 

In most cases, a "gelling agent is required both for the oil and the outside external phase. For the oil phase, fatty alcohols may be used. For the aqueous continuous phase one can use the same "thickeners that are used in emulsions, e.g. hydroxyethyl cellulose, xanthan gum, alginates, carrageenans, etc. Sometimes liquid crystalline phases are applied to stabilize the multiple emulsion droplets. These can be generated... 

A thickening coemulsifier can be added to the external water phase of W/ OAV multiple emulsions. The optimized emulsifier-coemulsifier pair at the interface will lead to improved packing, elasticity, and temperature stabihty of the final multiple emulsion. Furthermore more controlled release kinetics of release can be achieved (Terrisse et al, 1994). 

The conductometric analyses were carried out in correlation with the granulometric measurements, to determine the release of the encapsulated molecules. The study was carried out for different multiple emulsions prepared with the same lipophilic and hydrophilic surfactants, but with different dispersed mass fractions (20%, 30%, 40%) and thickened by the same hydrophilic polymer at various concentrations (0.5%, 1%, 2%). The release from an unthickened and very concentrated multiple emulsion (80%) was also measured. Figure 8.7 shows the evolution of the release rate as a function of the capillary number Ca, in order to take into account not only the shear rate but also the initial diameter and the viscosity values. 

The two kinds of multiple emulsions considered contained in the first formulation the EMP Hydrogel in the external phase (called TRME7) and in the second formulation thickening agent the EG 56 Hydrogel (denoted EGME). 

In the case of multiple o/w/o emulsions, as prepared by Yu [3-5], the process is that described by Jager-Lezer et al. [8j a primary o/w emulsion is dispersed in an oily external phase. CyDs are used to stabilize the primary emulsion, while a thickening agent dissolved in oil constitutes the stabilizer of the secondary external emulsion. Of course, some CyDs from the primary phase can also participate in the stabilization of the secondary emulsion. 

Uses Thickener and gellant for aq. formulations, esp. highly cone, salt sol ns., surfactants and drugs emulsifier of various oils to form stable multiple phase emulsions... 

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