HLB Values of Emulsifiers

TABLE 1.12 Magnitudes of Interfacial Tensions of Different Organic Liquids against Water (20°C)  

W/0 emulsions are formed by using HLB values between 3.6 and 6. This suggests that one generally uses emulgators that are soluble in oil phase. 

0/W emulsions need HLB values around 8-18. This HLB criterion is only a very general observation. However, it must be noticed that HLB values alone do not determine the emulsion type. Other parameters, such as temperature, properties of oil phase, and electrolytes in aqueous phase, also affect the emulsion characteristics. HLB values have no relation to the degree of emulsion stability. HLB values of some surface-active agents are given in Table 1.13. 

HLB values decrease as the solubility of surface-active agait decreases in water. The solubility of cetyl alcohol in water (at 25°C) is less than 1 mg/L. 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 applications in pulsion technology. It was shown that the HLB is related, in gaieral, to the distribution coefficient, K, of the anulsifier in oil and water phases  

HLB Values of Different Emulsifiers (Commonly Used in Emulsions) 

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Greth and Wilson [100] successfully applied, in the emulsion polymerization of unsaturated monomers, a method of classifying emulsifiers based on the HLB (hydrophilic/lipophilic balance) value. They plotted the most important properties of the emulsion polymerization system, i.e., the latex stability, particle size, emulsion viscosity, and rate of polymerization against the HLB value of emulsifiers used. The dependence is described by a curve with maximum or minimum at a certain value of HLB, as it is expected from the micellar model [6, 7]. 

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). 

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. 

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. 

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. 

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. 

As expected from the definition of the HLB value, materials with high HLB values are O/W emulsifiers and materials with low HLB value are W/O emulsifiers. An HLB value of 3-6 is the recommended range for W/O emulsification 8-18 is recommended for O/W emulsification. Since the requirements for emulsification of a particular ingredient differ markedly, depending on whether the ingredient is the dispersed phase (O/W emulsion)or the continuous phase (W/O emulsion), each ingredient has a different HLB value, depending on which phase of the final emulsion it will become. Thus, paraffinic mineral oil has an HLB value of 11 for emulsification as the dispersed phase in an O/W emulsion and a value of 4 as the continuous phase in a W/O emulsion. 

Values corresponding to surfactants or charged polymeric emulsifiers (only those actually synthesized) that lead preferentially to the formation of OAV and W/O emulsions appear respectively in white and black rectangles. Grey rectangles display HLB values of the most balanced emulsifiers. 

Primarily for toxicity reasons, work has focused on the use of nonionic surfactants, particularly Tweens and Spans. Pouton (20) and Wakericy el al. (21) have screened a range of surfactants, finding that in general molecules with unsat-uraced acyl chains were most efficiem emulsifiers, particularly the oleates with an HLB value of approximately II. The authors also reported that the sorbitan esters and ethoxylated triglycerides such as Tagat TO were more efficient than the fatty acid ethoxylates, possibly due to the polydispersity of the latter. 

The w/o/w or o/w/o emulsions are important, in particular when the protection of sensitive ingredients or controlled release of active substances is required [54]. Silicone-based emulsifiers are suited for these applications. They are strongly adsorbed at the oil interface, and do not migrate from one interface to the other, thus preventing the destabilization. Two emulsifiers have to be used to stabilize these multiphase emulsions. The hydrophilic-lipophilic balance (HLB) values of the emulsifiers should be above 10 for the hydrophilic emulsifier and below 6 for the hydrophobic emulsifier [54]. 

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. 

Sucrose acetate-isobutyrate may be emulsified readily with a surfactant mixture having an HLB value of 14, Table IV. The ester is heated to about 70°C and an inversion technique is used to produce an oil-in-water-type emulsion having excellent stability. As interest increases in water-based coatings as a means of reducing air pollution, it is significant that SAIB emulsions may be used in latex-based coatings ( ). 

For inducing coalescence, o/w emulsions were prepared using the different emulsifiers Tween 20, Tween 80, and Tween 65. The emulsifiers were used at a concentration of 1% m/m (above the CMC). Vegetable oil (Floreal Haagen, Germany) was used as dispersed phase. The hydrophiUc-Upophilic balance (HLB) values of each emulsifier, as well as the characteristics of the emulsions, are shown in Table 1. 

A tenside with a relatively strong lipophilic group and weak hydrophilic group is mainly soluble in oil and preferentially stabilizes a w/o emulsion, and vice versa. This fact led to the development of a standard with which the relative strength or activity of the hydrophilic and lipophilic groups of emulsifiers can be evaluated. It is called the HLB value (hydrophilic-lipophilic balance). It can be determined, e. g., from dielectric constants or from the chromatographic behavior of the surface-active substance. The HLB value of the fatty acid esters of polyhydroxy alcohols can also be calculated as follows (SV =... 

The free acid acts as a w/o emulsifier and the salts as o/w emulsifiers. The HLB-value of the sodium salt is 8-9, and that of the calcium salt, 6-7. The-sodium salt is used to stabilize an o/w emulsion which is subjected to repeated cycles of freezing and thawing. 

For application in food systems and preparation of w/o emulsions, emulsifiers with an HLB value of 3-6 are used, while for the preparation of o/w emulsions substances with an HLB value of 15-18 are used. Emulsifiers with an HLB value of 7-9 are commonly used as moisturisers (emollients). Approximate HLB values of certain emulsifiers and other surfactants are given in Table 11.15. For example, an emulsifier of HLB value 17 is needed for the preparation of an o/w emulsion of oleic acid, an emulsifier of HLB value 9 for beeswax emulsion, an emulsifier of HLB value 6 for rapeseed oil and cocoa butter emulsions and an emulsifier of HLB value 5 for pork lard emulsion. In practice, mixtures of two compatible... 

Once relatively stable emulsions are identified, the loading of emulsifier can be reduced to fine tune the system. One needs to decide whether an o/w or a w/o emulsion is better for their particular application. As an example, if a 50 50 Span/Tween mixture was the best, then the required HLB would be 9.8 for this particular system. Having the HLB of the liquid then allows the formulator to search publications (22, 23) for emulsifiers or mixtures of emulsifiers that have chemical compositions compatible with the liquid in addition to having the appropriate HLB. The required HLB values of common organic liquids, oils, and waxes are also available in the literature. 

Release agents usually have lipophilic properties and are usually added to spray suspensions. They prevent agglomeration of cores during film formation. Preferably used are talc, Mg or Ca stearate, ground silica, kaolin or nonionic emulsifiers with an hydrophile-lipophile balance, HLB, value of between 3 and 8. Standard amount of release agents is 0.5 phr. ... 

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