HLB Value

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). 

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. 

These characteristics are typically classified as a hydrophile-lipophile balance (HLB value). For example, hydrophilicity may be denoted within a range of 2 to 20, with true solutions being obtained at HLB values >14 and poor dispersibility occurring at HLB values <6. Oil-in-water emulsification requires a high HLB value surfactant, while water-in-oil emulsification needs a low HLB value surfactant. 

Asphalts and waxes can be removed by dissolving in hot naphtha for 3 to 4 hours. The naphtha benefits from the addition of 0.1% of a water-soluble surfactant (HLB value of 15-20, such as polyethylene glycol 600 monolaurate) and 0.1% of an oil-soluble surfactant (HLB value of 0-5, such as propylene glycol monstearate). The solution must be circulated fill-and-soak methods are unsatisfactory. 

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. 

Surfactants employed for w/o-ME formation, listed in Table 1, are more lipophilic than those employed in aqueous systems, e.g., for micelles or oil-in-water emulsions, having a hydrophilic-lipophilic balance (HLB) value of around 8-11 [4-40]. The most commonly employed surfactant for w/o-ME formation is Aerosol-OT, or AOT [sodium bis(2-ethylhexyl) sulfosuccinate], containing an anionic sulfonate headgroup and two hydrocarbon tails. Common cationic surfactants, such as cetyl trimethyl ammonium bromide (CTAB) and trioctylmethyl ammonium bromide (TOMAC), have also fulfilled this purpose however, cosurfactants (e.g., fatty alcohols, such as 1-butanol or 1-octanol) must be added for a monophasic w/o-ME (Winsor IV) system to occur. Nonionic and mixed ionic-nonionic surfactant systems have received a great deal of attention recently because they are more biocompatible and they promote less inactivation of biomolecules compared to ionic surfactants. Surfactants with two or more hydrophobic tail groups of different lengths frequently form w/o-MEs more readily than one-tailed surfactants without the requirement of cosurfactant, perhaps because of their wedge-shaped molecular structure [17,41]. 

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 ... 

The HLB values required for the emulsification of commonly used oils and waxes in pharmaceutical applications are given in Table 7 [143]. To obtain a... 

Table 5 HLB Values of Surfactants Commonly Used in Pharmaceutical Products... 

Table 6 Relationship Between the Use of Surfactants in the Preparation of Pharmaceutical Dosage Forms, Their Dispersibility in Water and Their HLB Values...

Table 7 Required HLB Values for the Emulsification of Oils and Waxes Commonly Used in Pharmaceutical Applications... 

As explained earlier, however, the actual constitution of a surfactant rarely conforms to its nominal structure. Consequently the theoretical method of calculation is of limited utility, practical methods being more reliable. The HLB value may be determined directly by analysis or by comparison with a range of surfactants of known HLB values. An analytical method for the sorbitan monolaurate described above uses Equation 9.2 [37]. 

Once the HLB values of a range of surfactants are known it is an easy matter to calculate the HLB value of a mixture as follows ... 

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. 

The adverse effect of nonionic adducts of low cloud point can be avoided by the use of hybrid agents of the ethoxylated anionic type, variously and confusingly referred to as modified nonionic , modified anionic or weakly anionic types. Thus Mortimer [113] has proposed the use of products of the ethoxylated phosphate type (12.27). In this structure, R, as well as the degree of ethoxylation (n) may be varied to optimise the overall HLB value. The numerous ether groups are said to enhance the dye-solubilising and levelling capacity, whilst the polyphosphate grouping exerts several useful effects [113]. These compounds ... 

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 (hydrophile-lipophile balance) system, 70 126 HLB value, 72 54, 55 HMG-CoA, role in cholesterol synthesis, 5 142... 

Step 1 The dominant quality factors here are convenience and the ability to deliver the precise dosage for applications. Optimum HLB is an important factor for convenience (Table 2). As in example 1, an HLB value between 3 and 15 is desirable for the detergency property, preferably towards the high end to give clear appearance (Figure 1). Thus, HLB0p is set to be 15. 

The i value and HLB value of polyhydroxyl and polycarboxylic xanfhates are calculated and shown in Table 5.5. It is obvious that the polyhydroxyl xanthate with more hydroxyl groups and polycarboxylic xanthate with more carboxylic groups have greater i or HLB value. Taking the i or HLB values as x-axis and the flotation recovery of arsenopyrite or pyrrhotite at depressant concentration... 

Figure 5.38 Flotation recovery of arsenopyrite and pyrrhotite as a function of HLB] value of poly hydroxyl xanthates...

Relationship between HLB values of nonionic surfactant ethers and esters and the nasal absorption of insulin (lOU/kg) in rata measured as a percentage reduction (D) in glucose levels from 0-4h. Surfactant applied at a concentration of 1 . 9 ethers, 0 esters. Data... 

That is, nonionic surfactants caused an increase in the Stokes radius (R) of the particles due to penetration of the phospholipid surface layer and unfolding of apoprotein B molecules leading to particle assymetry at molar ratios of surfactant LDL2 of ca. 1000/1. At higher molar ratios, corresponding to 1-2 moles surfactant per mole of phospholipid, ionic surfactants and nonionics with HLB values < 14.6 caused rapid decreases in the Stokes radius due to breakdown of LDL2 into the lipid surfactant and protein surfactant micelles. 

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