Emulsifier HLB-value

This dimensionless scale ranges from 0 to 20 a low HLB (<9) refers to a lipophilic smfactant (oil soluble) and a high HLB (> 11) to a hydrophilic (water soluble) surfactant. In general, W/O emulsifiers exhibit HLB values in the range 3-8 while O/W emulsifiers have HLB values of about 8-18. There exist empirical tables of HLB values required to make emulsions out of various materials [44] and tables and equations to determine emulsifier HLB values [10,44,46]. If the value is not known, then a series of lab emulsification tests are required, using a series of emulsifying agents of known HLB values. 

Emulsifiers are classified by the hydrophilic—lipophilic balance (HLB) system. This system indicates whether an emulsifier is more soluble in water or oil, and for which type of emulsion (water-in-oil or oil-in-water) it is best suited. Emulsifiers having alow HLB value are more oil soluble, and are better suited for water-in-oil appHcations such as margarine. Conversely, emulsifiers having a high HLB value are more water soluble, and function more effectively in oil-in-water emulsions such as ice cream (34). The use of this system is somewhat limited because the properties of emulsifiers are modified by the presence of other ingredients and different combinations of emulsifiers are needed to achieve a desired effect. The HLB values of some common emulsifiers are given (35). 

The hydrophile—hpophile balance (HLB) is an empirical system based on the fact that oil—water (o/w) emulsions are best stabilized by water-soluble-emulsifiers and water—oil (w/o) emulsions are best stabilized by oil-soluble ones (3). The HLB scale mns from 0—20 and is based on the ratio of the saponification number of ester, A, to the acid number of recovered acid, where HLB = 20 1-Sj A). The dispersibiUty of an emulsifier in water is related to HLB value. 

Table 3 gives HLB values of some of the important emulsifiers. The HLB optimum for a given emulsifier varies with the components of the food system. A coconut oil—water emulsion that shows optimum stabiUty with an HLB of 7—9 shows a shift ia requirements for stabiUty upon addition of caseia and electrolytes to an optimum stabiUty usiag an emulsifier having an HLB of 3—5. In addition, the stabiUty of an emulsion can be affected by the chemical nature of the emulsifier. The optimum HLB for an emulsifier ia a given system is iafluenced by the other iagredients as is illustrated for a model synthetic milk system ia Figures 1 and 2. 

The polymeric latex obtained in a hydrophobic organic solvent is poorly dispersed in water because of the presence of an emulsifier with a low HLB value. For this reason, a wetting agent is added to water or emulsion prior to the dissolution. The wetting agent (a surface active substance with a high HLB value) facilitates the inversion of latex phases to produce a direct type emulsion. Usually, it belongs to oxyethylated alkylphenols, fatty alcohols, or fatty acids. 

Oily surfaces can be deoiled by using a high HLB value emulsifier such as dioctylsulfosuccinate, together with antifoam, applied either as a hot-water soak or pressure washed. 

Formation of emulsions of the oil-in-water or water-in-oil type depends mainly on the hydrophilic-lipophilic balance (HLB) of the emulsifier. Phosphate esters with their various molecular structures can be adjusted to nearly every HLB value desired. Therefore they are able to meet nearly all of demands in this field. 

HLB value of the oil phase. Further tests can then be carried out with different chemical types of agents around this effective HLB value in order to find the optimum emulsifying system. 

One advantage of sucrose esters is that they can be made with a wider range of HLB values than other emulsifiers (Figure 3). Chemically, the families of emulsifiers shown in Figure 3 are all esters. As an emulsifier... 

HLB Values of Different Emulsifiers Commonly Used in Emulsions... 

HLB values decrease as the solubility of the surface-active agent decreases in water. Solubility of cetyl alcohol in water (at 25°C) is less than a milligram per liter. It is thus obvious that, in any emulsion, cetyl alcohol will be present mainly in the oil phase, while SDS will be mainly found in the water phase. Empirical HLB values are found to have significant use in emulsion technology applications. It was shown that HLB is related, in general, to the distribution coefficient, KD, of the emulsifier in the oil and water phases ... 

The relation between HLB and emulsion stability and structure could be suggested based on this thermodynamic relation. HLB values can also be estimated from the structural groups of the emulsifier (Table 9.4). 

Ice cream emulsion has a very characteristic degree of stability. The air bubbles should remain dispersed, but as soon it melts in the mouth, the emulsion should break. This leads to the sensation of taste, which is very essential to enjoy its specialness. The sensation of taste on the surface of the tongue is known to be related to molecular shape and physicochemical properties. As soon as these molecules are separated from the emulsion, the taste sensation is recorded in the brain. Therefore, the various components must stay in the same phase after the breakup of the emulsion. Emulsifiers that are generally used have low HLB values (for W/O), and have been found to have considerable effect on the structure of the ice cream. 

Non-aqueous HIPEs have received even less attention indeed, to date, there have been only two publications dealing with this subject, to the authors knowledge [124,125]. These describe the preparation of highly concentrated emulsions of jet engine fuel in formamide, for use as safety fuels in military applications. The emulsifier system used was a blend of two nonionics, with an optimal HLB value of 12. 

Experiments on the stability of the HIPEs indicated that one of the most important factors was the solubility of the emulsifier in the continuous (formamide) phase. Thus, the higher the surfactant solubility, the more stable the emulsion. The emulsifier concentration was also important stability increased to a maximum, then decreased, with increasing surfactant concentration. Surprisingly, the HLB number did not appear to have much effect on the stability of the emulsions, over the range studied (11 to 14). This was attributed to the high concentration of emulsifier in the continuous phase, although the narrow HLB value range is probably also a factor. 

Very surface-active emulsifiers (nigh HLB value) are capable of forming micelles in water. The latter is in equilibrium with emulsifiers at the air-water interface. At a certain concentration (= critical miceile concentration, CMC) the surface will be saturated with emulsifier and no further reduction in surface tension will be observed. The CMC can be found by surface tension measurements according to Figure 20. 

Monoglycerides and mono-diglycerides have low HLB values and cannot form micelles. They build up a multi-layer at the surface, resulting in a constantly decreasing surface tension as their concentration increases. However, in systems with proteins such as fat-free ice cream mixes, these emulsifiers behave as if they have a CMC. A possible explanation for this observation is that the unbound emulsifier in the fat-free mix is in equilibrium with the protein-bound emulsifier. Above a certain concentration of emulsifier in the mix, any surplus of emulsifier will adhere to the protein in the water phase after the surface has been saturated. The unadsorbed emulsifier is seen as very small crystals less than 200 nm by electron microscopy analysis4. ... 

The amphiphilic nature of many emulsifying agents (particularly non-ionic surfactants) can be expressed in terms of an empirical scale of so-called HLB (hydrophile-lipophile balance) numbers222 (see Table 10.1). The least hydrophilic surfactants are assigned the lowest HLB values. Several formulae have been established for calculating HLB numbers from composition data and they can also be determined experimentally - e.g. from cloud-point measurements123,125. For mixed emulsifiers, approximate algebraic additivity holds. 

The hydrophile-lipophile balance (HLB) system is the measure of the surfactant s polarity as well as other physical properties of surfactants and the emulsifying materials. The more lipophilic the surfactant is, the lower the HLB values will be. Table 4.5 empirically classifies and compares surfactants according to their optimum use. Table 4.6 shows the HLB values for a selected group of surfactants. The HLB value of the surfactant or surfactant mixture should be matched with that of the oil or the mixture of oils to ensure a stable emulsion. The required HLB values of a... 

The hydrophilicity of nonionic surfactants can be characterized numerically as their hydrophile-lipophile balance (HLB). An HLB value of 3-6 indicates that the compound is a likely W/O emulsifier 7-9, a wetting agent 8-13, an O/W emulsifier 13-15, a detergent and 15-18, a solubilizer (of oil or other nonpolar compounds) in water. The HLB values of some common compounds are presented in Table 34.12.170 An HLB value of 8.0 is shown in Table 34.12 for lecithin, but manufacturers are able to supply modified lecithins with values of2-12. 

Polyglycerol esters of fatty acids are produced by reacting polymerized glycerol with edible fats. The degree of polymerization of the glycerol and the nature of the fat provide a wide range of emulsifiers with different HLB values. 

Figure 4.3 Comparison of the range of HLB value obtainable with different ester emulsifiers...

The oil structure influence on the formulation is illustrated in Figure 1. It represents the minimum percentage of emulsifiers required to induce the transition aacro-raicroeaulsion versus their HLB values for monomer-water mixtures dispersed in different oils. It can be seen that in the case of acrylamide (AH) or acrylamide-sodium acrylate (Aa) mixtures, the amount of surfactant needed to form a microemulsion is much larger for toluene or cyclohexane than for Isopar K (11,12[). When methacrylcxyethyltrimethylammonium chloride (HA0OU.AT) is the monomer, the optimal conditions are obtained in cyclohexane. These results closely follow the differences calculated for the solubility parameters between oils and lipophiles as shown in Table I. 

The conditions which have been defined for the formation of effective microemulsions (nature of the oil, Ro and HLB values) are also required for obtaining clear and stable microlatices after polymerization. Various water-soluble monomers have been polymerized by a free radical process in anionic and nonionic microemulsions, either under U.V. irradiation or thermally with AIBN as the initiator (11,14,22,29). Total conversion to polymer was achieved in less than 20 minutes (a few minutes in some cases). Series of experiments have been performed in various oils. Table III summarizes some of the results and emphasizes the importance of the formulation. A good chemical matching between oils and emulsifiers (G 1086 -t Arlacel 83, Isopar H) leads to stable latices, a poor matching (G 1086 Arlacel 83, heptane) leads to unstable latices which settle within a few hours to a few days (22). 

The manner in which lecithin is modified to achieve increased hydrophilicity will greatly affect its emulsification properties. Different modifications will create lecithin products with different apparent HLB (hydrophile-lipophile balance) values, a term used to convey the approximate degree of water dispersibility (hydrophilicity) of lecithin products (31). The higher its HLB value, the more water dispersible the lecithin product. In o/w emulsions, the type of fat to be emulsified may require a specific type of hydrophilic lecithin for optimum emulsion stability. Dashiell (31) provides a short listing of fat types, and the corresponding class of lecithin found to give the most stable emulsion in model systems of water/fat/ emulsifier. 

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