HLB system

In spite of many advances in the theory of stability of lyophobic colloids, resort has still to be made to an empirical approach to the choice of emulsifier, devised in 1949 by Griffin. In this system we calculate the hydrophile-lipophile balance (HLB) of surfactants, which is a measure of the relative contributions of the hydrophilic and lipophilic regions of the 

Typically, the polysorbate (Tween) surfactants have HLB values in the range 9.6-16.7 the sorbitan ester (Span) surfactants have HLBs in the lower range of 1.8-8.6. 

For those materials for which it is not possible to obtain saponification numbers, for example beeswax and lanolin derivatives, the HLB is calculated from 

Chapter 7 Emulsions, suspensions and other disperse systems 

Polysorbate 20 has a molecular weight of approximately 1300 and contains 20 oxy-ethylene groups and two sorbitan rings. Thus, 

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The use of the HLB system can be illustrated as follows. Suppose that a certain... 

The HLB system has made it possible to organize a great deal of rather messy information and to plan fairly efficient systematic approaches to the optimiza-tion of emulsion preparation. If pursued too far, however, the system tends to lose itself in complexities [74]. It is not surprising that HLB numbers are not really additive their effective value depends on what particular oil phase is involved and the emulsion depends on volume fraction. Finally, the host of physical characteristics needed to describe an emulsion cannot be encapsulated by a single HLB number (note Ref. 75). 

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). 

An a priori method for choosing a surfactant was attempted by several researchers (50) using the hydroph i1 e—1 ip oph i1 e balance or HLB system (51). In the HLB system a surfactant soluble in oil has a value of 1 and a surfactant soluble in water has a value of 20. Optimum HLB values have been reported for latices made from styrene, vinyl acetate, methyl methacrylate, ethyl acrylate, acrylonitrile, and their copolymers and range from 11 to 18. The HLB system has been criticized as being imprecise (52). 

Particularly useful is the physical classification of surfactants based on the hydrophile-lipophile balance (HLB) system [67,68] established by Griffin [69,70]. More than 50 years ago he introduced an empirical scale of HLB values for a variety of nonionic surfactants. Griffin s original concept defined HLB as the percentage (by weight) of the hydrophile divided by 5 to yield more manageable values ... 

Griffin studied primarily ethylene oxide (EO) adducts and routinely substituted % EO for % hydrophile. Since that time, the HLB system has become very popular, especially to characterize emulsifying agents. (The reader is referred to sec. V.B. for a more detailed discussion of the use of the HLB system for the identification of adequate emulsifiers and combinations thereof.)... 

The HLB system - a time-saving guide to emulsifier selection, Publication 103-3 10M (Wilmington ICI Americas,... 

The HLB concept, introduced in Section 3.6.1 is probably the most useful approach to predicting the type of emulsion that will be stabilized by a given surfactant or surfactant formulation. The HLB concept was introduced [207,209] as an empirical scale that could be used to describe the balance of the size and strength of the hydrophilic and lipophilic groups on an emusifier molecule. Originally used to classify Imperial Chemical Industries non-ionic surfactant series of Spans and Tweens the HLB system has now been applied to many other surfactants, including ionics and amphoterics. 

There is some evidence to suggest that, depending upon the phase volume ratios employed, the emulsification technique used can be of greater importance in determining the final emulsion type than the H LB values of the surfactants themselves [434], As an empirical scale the HLB values are determined by a standardized test procedure. However, the HLB classification for oil phases in terms of the required HLB values is apparently greatly dependent on the emulsification conditions and process for some phase-volume ratios. When an emulsification procedure involves high shear, or when a 50/50 phase volume ratio is used, interpretations based on the classical HLB system appear to remain valid. However, at other phase-volume ratios and especially under low shear emulsification conditions, inverted, concentrated emulsions may form at unexpected HLB values [434]. This is illustrated in Figures 7.4 and 7.5. 

Applications. N-octadecylphthalamate has been commercialised as an emulsifier for high HLB systems (water in oil) for cosmetic creams and lotions. The emulsions made using this product are very fine and it is claimed that a much richer skin feel can be obtained with lower oil content, compared to conventional emulsifiers. 

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 HLB system used above does not take into consideration the temperature effects. Upon heating, an O/W emulsion prepared with nonionic surfactants inverts to a W/O emulsion because the hydrogen bondings in the polyoxyethylene groups are broken, and the HLB value of the surfactant becomes smaller. The higher the... 

An emulsifier system must cause the concentrate to disperse spontaneously into small, stable droplets when mixed with water. To accomplish this, the surfactant system must have a most favorable solubility relationship a proper balance between oil and water solubility or, in other words, a favorable hydrophile-lipophile balance in solubility. This balance in solubility is frequently referred to as HLB and was first described by Griffin (6). However, the HLB system is based on the structure of a surfactant molecule and, therefore, predicts the behavior of a single molecule. It does not take into account tr 3 fact that many surfactants form micelles in organic solutions. If a micelle is formed, its HLB may have no relationship to the HLB of the monomer unit. Therefore, to select an emulsifier well, we will need a better understanding of the behavior of surfactants in organic solvents. 

The ratio of the hydrophilic and the hydrophobic groups of the surfactant molecules, that is, their hydrophile-lipophile balance (HLB), is also important in determining interfacial him curvature and consequently the structure of the ME. The HLB system has been used for the selection of surfactants to formulate MEs and accordingly the HLB of the candidate surfactant blend should match the required HLB of the oily component for a particular system furthermore a match in the lipophilic part of the surfactant used with the oily component is favorable [7],... 

The HLB System, Chemmvinique Reprint. ICI United States, Inc., Chemical Specialties Division, Wilmington, DE, 1976. 

A limitation of the HLB system is that other factors are important as well. Also, the HLB is an indicator of the emulsifying characteristics of an emulsifier but not the efficiency of an emulsifier. Thus, although all emulsifiers having a high HLB will tend to promote OAV emulsions, the efficiency with which those emulsifiers act will vary considerably for any given system. For example, usually mixtures of surfactants work better than pure compounds of the same HLB. 

The HLB system has heen put on a more quantitative basis by Davies, who calculated group contributions (group numbers) to the HLB number such that the HLB was obtained from... 

For reasons not explained by the HLB system, hut from other approaches, mixtures... 

The HLB system has several drawbacks. The calculated HLB, of course, cannot take account of the effect of temperature or that of additives. The presence in emulsions of agents which salt-in or salt-out surfactants will... 

Apart from the fact that the use of the HLB system is limited as it is based on the observation of creaming or separation of the emulsions, as an index of instability the HLB system also neglects the effects of surfactant concentration on stability (26) and of course it is irrelevant to the particular problems with multiple emulsion systems. Nevertheless, it provides a useful approach to the choice of optimal surfactant system. In general, in a w/o/w emulsion, the optimal HLB value of the primary surfactant will be in the range 2-7 and in the range 6-16 for the secondary surfactant. Equilibration of the systems after mixing will undoubtedly result in the transfer of surfactant between the aqueous and nonaqueous components. Saturation of the phases with the two surfactants used should prevent instability during this equilibration. 

Four different emulsifier selection methods can be applied to the formulation of microemulsions (i) the hydrophilic-lipophilic-balance (HLB) system (ii) the phase-inversion temperature (PIT) method (iii) the cohesive energy ratio (CER) concept and (iv) partitioning of the cosurfactant between the oil and water phases. The first three methods are essentially the same as those used for the selection of emulsifiers for macroemulsions. However, with microemulsions attempts should be made to match the chemical type of the emulsifier with that of the oil. A summary of these various methods is given below. 

HLB values of the surfactants 6a-c, f, g and llg have also been evaluated experimentally by using the required HLB concept of the oil/water system [40]. The HLB system predicts the optimum emulsion stability when the HLB value of the surfactant systems matches the required HLB of the oil/water system. The required HLB is the value at which enhanced emulsion stability will be attained. Optimization of the performance can be achieved by only including surfactant systems with similar HLB values. Mixtures composed of a mannuronate-type surfactant and a commercial cosurfactant with a known HLB value (Span 85, Brij 72, Span 40, Span 20) were formulated with various surfactant/cosurfactant ratios (20, 40, 60, and 80 wt%) to create different HLB values of the system. Then, the performance was determined and plotted vs the HLB. A maximum appears in the plot and the... 

ICI Americas (1976) The HLB System-A Time Saving Guide to Emulsifier Selection. Atlas Division, Wilmington. 

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