J. Soc. Cosmetic Chemists, 19, 129-136 (Feb. 5, 1968)

A Titration Method for

Determination of the

HLB's of Emulsifiers

the

JAMES J. MIDDLETON, B.A., M.B.A.*

Presented May •, 1967, New York City

Synopsis--A titration method for determining HLB's, particularly of emulsifiers, is pre- sented. This is a color-migration procedure, similar to the Epton method for determining anionics or cationits. Parameters of variables are discussed, especially as to the control of errors and their magnitude for any one variation. Application to the determination of the HLB requirements of mixed-oil phases is also discussed.

INTRODUCTION

The HLB concept (hydrophile-lipophile balance of a nonionic emulsifier) was introduced by Griffin (1). It has since been refined and extended by Griffin, Carter, and their group (2, 3), and summarized by Griffin (4). The practical value of the system to technical people in the cosmetic, detergent, and emulsion fields has been amply demonstrated. This system provides a unifying method which embraces several families of surfactants, and divides the effort required to select the most effective agent to use in a particular project.

The HLB of an emulsifier is a number which expresses the ratio be- tween water-soluble groups and oil-soluble groups in the molecule. The higher the HLB number, the more water-directed is the entire molecule. Surfactants of a given chemical type can be arranged in a series, starting with the most oil-directed and advancing to the most water-directed as

* Millmaster-Onyx Corp., Onyx Chemical Co. Div., 190 Warren Street, Jersey City, N. J. 07302.

129

130 JOURNAL OF THE SOCIETY OF COSMETIC CHEM1STS

the numbers increase. Such series include the Span ©* and Tween ©* group and the Neutronyx©• surfactants. There are, of course, other tradename series too numerous to list here.

Several authors have reported attempts to relate HLB to various other properties of the surfactant molecules (5-8). At present, how- ever, the most direct method, which at the same time includes factors in addition to the HLB itself, is actually to make a set of emulsions, using the desired oil phase, and varying the HLB throughout the set in a regu- lar manner. HLB values intermediate between those of commercial

products can be achieved by mere mixing of these products. For ex- ample, blending 70% Tween 80 (HLB of 15) and 30% Span 80 (HLB of 4.3) (0.70 X 15) + (0.30 X 4.3) = 11.8, HLB of the blend. Thus, a higher-HLB emulsifier is mixed with a lower-HLB emulsifier in such pro- portions that the average HLB's of the several mixtures as calculated show a regular variation. The emulsions in the series are then com- pleted, and their stabilities are observed. The most stable ones cluster around a particular HLB range. Then, another set of emulsions is made, to range more compactly around this HLB stability-peak and sub- divide the values more finely than in the first set. This narrowing down process can be carried out further until an almost infinitesimal range is covered; but there is a practical limit of refinement left to the judg- ment of the chemist.

It is perfectly proper to speak of the HLB of a nonsurfactant, such as mineral oil. In this sense, we refer to the HLB required by the mineral oil to become emulsified, even though the oil itself has no duality of both oil- and water-solubility. In fact, mineral oil requires an HLB of 10 to become emulsified in water, and an HLB of 1.8 to form a water-in-oil

system. The author has found that, for preliminary screening, a rapid titra-

tion procedure is highly useful. Briefly, a water solution of the higher- HLB material is titrated with a solution of the lower-HLB material, in the presence of the oil phase. An indicator is used, the most dependable found so far being a carbon black. At the end point, the carbon mi- grates from the water phase into the oil, with high visibility. Under the experimental conditions detailed below, emulsification of the oil does not occur at the end point, and the phase separation is rapid. The crucial effect seems to be on the carbon black itself rather than on the oil phase, although this is still somewhat conjectural.

* Atlas Chemical Industries, Inc., Wilmington, Del. t Onyx Chemical Co., Jersey City, N.J.

DETERMINATION OF HLB 131

Figure 1. Titration with Neutronyx 640 and 626 ©, Lorol //5. © Left, before end point; Center, at end point; Right, after end point

EXPERIMENTAL

Ten per cent water solutions are made of the emulsifier under test, and also of an emulsifier with known HLB. The lower HLB surfactants

ordinarily require a hydro-alcoholic solvent, but the alcohol content should be kept as low as possible. Water solutions are preferred, even if they are cloudy, as long as they are stable.

Ten milliliters of the higher-HLB solution are added to a 100-ml grad- uated cylinder. About 0.1 g carbon black* is added, and the cylinder is shaken to wet out and disperse the pigment. Water is added to total about 80 ml. Ten grams of the selected oil phase is added and the con- tainer is shaken gently to mix the contents without generating a great deal of foam. The low-HLB solution is added in increments from a

burette. Unless one can estimate in advance the probable titrant vol- ume and thus approach it rapidly, it is well to start with 1-ml additions, shaking after each, then allowing the phases to separate. The end point is taken as an apparently even division of black between the two phases. Figure 1 shows such a titration. The oil phase is lauryl alco- holt and the two surfactants used are ethoxylated nonyl phenols, Neu- tronyx //640 and //626, with emulsifying HLB's of 15 and 10.7, respec- tively. The center cylinder shows the end point at the calculated mix-

* Carbon Black, Vulcan #9 ©, Godfrey L. Cabot Co., 125 High St., Boston, Mass. ,+ Lorol #5, © E. I. dupont de Nemours & Co., Wilmington, Del.

132 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

16

14

12

I I I I IHLB I (Tran, 'sfer) 2 4 6 8 10 12 14 16,

Figure 2. Correlation of transfer or titration end point HLB with o/w emulsification HLB requirement: 1. Lorol #b ©, 2. Butyl Myristate, and 3. Klearol© mineral oil

ture HLB of 12.66. On the left is a titration with 0.5 ml less titrant, and on the right, with 0.5 ml more. This is a fine example of the precision of the method when carefully performed, since despite the great visible dif- ferences, the HLB's are, from left to right, 12.70, 12.66, and 12.62, as cal- culated from the known quantities of the two emulsifiers used, and their known HLB values.

Similar titrations utilizing the same Neutronyx, with mineral oil* as the oil phase, gave a value of 3.6 for the end point. Butyl myristate showed an end point at 6.

CALCULATIONS

The published HLB requirements for the emulsification of lauryl al- cohol or mineral oil into water are 14 and 10, respectively (9). The same reference includes the HLB requirement of 11 for butyl myristate. When these emulsification values were compared with the values shown by our carbon black migration end points, a straight-line relationship, graphically, was found (Fig. 2). The line-locus is y = 0.45x -[- 8.3; y

* Klearol©, Sonneborn Division (Witco Chemical Co.), 277 Park Ave., New York, N.Y.

DETERMINATION OF HLB 133

being the O/W emulsification HLB requirement, and x the HLB found by the carbon black titration. To date, all relatively pure chemicals which have been standardized and which have O/W HLB values published agree with this relationship.

It might appear from the graph of Fig. 2 that oil phases having an HLB requirement below 8 cannot be characterized by this titration method. In a few cases, the author has performed titrations which gave negative values after calculating the end point HLB. When these nega- tive values were substituted into the line equation, however, O/W HLB values resulted which were below 8, and quite verifiable by preparing a stable emulsion therewith.

APPLICATIONS

Although this method has been applied successfully in several tech- nical service problems having to do with emulsifying, no attempt to de- velop a library of HLB values for commercial emulsifiers, or for oils, has been made. Many emulsifier values have been published by sup- pliers or are available from the suppliers concerned.

As is true in all experimental or analytical work, precautions must be taken, limitations of a method must be recognized, and good judgment must be used. Also, unfortunately, there will probably always be in- stances when a method just won't work because of undetermined inter- ferences.

The carbon black selected is fine enough to disperse into an intensely black suspension, but it is very important that it actually be well dis- persed initially. With certain types of nonionics which may not wet- out well, even though the HLB is high, it is best to start a fresh cylinder with 1 ml of a 10% solution of another nonionic of known HLB that is a good dispersant, add and wet-out the carbon black, and make up to the 10 ml specified with the high-HLB solution under test. Once the carbon is dispersed, it will ordinarily remain so. The dispersant added must be included in the final calculation of the end point HLB.

It is necessary to shake the cylinder just before each addition of ti- trant. If titrant is added to the oil phase directly, floating at the top as it does, the local concentration of low-HLB titrant thus added into the

oil will usually distort the end point. A sufficiently low HLB will oil- wet the carbon whether this HLB is reached in the normal course of the

titration or accidentally. The carbon presumably cannot distinguish the intention of the chemist. Once wet by the oil, the carbon does not readily divest itself to become once more water-wet. This appears to be

134 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

the greatest single source of error both by preventing a thorough mixing of the two emulsifiers in the water phase, and by coloring the oil-layer prematurely. For this reason, the method calls for titrating a higher HLB with a lower one, and does not offer the alternate choice.

It is possible in some systems, especially in preliminary screening runs, to pass through the optimum HLB for forming an O/W emulsion with the oil phase. While this is not the titration end point, it is still an analytical nuisance. Continuing the titration should be attempted, and eventually the emulsion should break up. In the case of lauryl alcohol, however, the emulsion may be a quite compact mass and form more or less of a plug at the top.

In case of difficulty, two alternatives are offered. First, one can start all over again, using a different substrate to begin with, having an HLB below the value of 14 published as optimum for the O/W emulsifi- cation of lauryl alcohol. Or, one can set up a series of step-wise titra- tions in which both the high and the low HLB solutions are premixed in the cylinders and brought up to volume before the lauryl alcohol is added. Now, observations after shaking can be lined up, and the titra- tion HLB closely estimated. This alternative is reminiscent of the mak- ing of an emulsion series to determine HLB values, but it is far faster. Each phase separation will be complete enough to be evaluated in under five minutes, even if the entire 10 ml of oil does not separate out in that time.

To determine the HLB of an unknown emulsifier, a simple oil of known HLB requirement is selected, and titration is performed with so- lutions of the unknown surfactant and one of known HLB. Another

common problem is to determine the proper O/W emulsification HLB requirement of a mixed oil phase that has already been selected. The author usually starts a trial with solutions of emulsifiers with extremes of HLB. Thus, a range for the end point is found quickly. This can be further refined by repeating the titration with two surfactants both somewhat closer to this range.

One difficulty with this method is the evident requirement that the oil phase must be liquid at room temperature, so that the carbon can distribute, and so that the oil phase can separate out homogeneously. Bearing in mind that not only are the HLB's of emulsifiers additive in mixtures, but that the same holds true for oil-phase HLB requirements, the author has worked with toluene solutions of petrolatum. It appears that the additive function works very well so long as the petrolatum re- mains dissolved; that is, as long as the concentration is below that of a

DETERMINATION OF HLB 135

saturated solution. HLB's of these mixtures titrated with increasing accuracy as the content of petrolatum was increased.

EFFECTS OF OTHER FACTORS

The effects of added electrolyte, alcohol, and increased temperature are of minor influence when relatively small changes are made in these parameters. Above certain levels, the effects become so large that the author has not yet been able to measure them completely with accept- able accuracy.

Up to 1% electrolyte in the titration is tolerable, whether acetic acid, sodium or potassium chloride, or aluminum salts, so long as no chemical reaction occurs in the system. Up to about 10% alcohol, ei- ther ethyl or isopropyl, can also be accommodated. Temperatures to 35 øC induce little change. Above this, titration HLB's rise rapidly (considerably more of the low HLB titrant must be added) and duplica- tion of results becomes difficult.

The fact that these three factors change the HLB of a system is of great interest. Those who develop emulsion products are aware that any one of these can destroy an otherwise elegant formulation. It is therefore suggested that titrations be performed after including the elec- trolyte or alcohol in the water phase. This may ease later efforts to as- sure stability. As to temperature, stable emulsions have been found to separate after oven storage. The change of HLB requirement reported here may be a sufficient explanation, although not a remedy. Possibly supplying an HLB intermediate between the two may offer stability at both oven and room-temperature conditions.

These three factors most likely operate by changing the hydration of the ethylene oxide chains, thereby altering the micelle structure and critical micelie concentration of the system.

The method has other built-in bonuses, which can be used with in-

genuity to solve many difficult cases, sometimes almost accidentally. The author had occasion recently to emulsify a very dark colored oily material. Obviously, a prior determination of the HLB was desirable. While dubious that any darkening of the oil from the carbon migration would be observable, the titration was tried anyway. To observe the darkening was, indeed, hopeless. But, rewardingly, at one point the water phase suddenly became almost white as the carbon transferred into the oil, not only demonstrating the end point, but also greatly relieving one anxious chemist. The HLB determined was, actually, quite cor-

136 JOURNA L OF THE SOCIETY OF COSMETIC CHEMISTS

rect, as shown by the stable emulsions later compounded using the con- verted O/W HLB.

This titration method, while probably not foolproof, is a convenient and easy means for rapidly developing information to prepare specific emulsion formulations. The choice of emulsifiers is quickly narrowed down, and the application range of a new emulsifier is quickly deter- mined. In the hands of a skilled chemist, many of its shortcomings can be avoided, and the procedure probably can be improved into greater usefulness as experience with it grows.

(Received May 19, 1967)

REFERENCES

(1) Griffin, W. C., Classification of surface-active agents by "HLB," J. Soc. Cosmetic Chem~ ists, 1,311-26 (1949).

(2) Griffin, W. C., Calculation of HLB Values of non-ionic surfactants, Ibid., 5, 249-55 (1954).

(3) Griffin, W. C., Clues to surfactant selection offered by the HLB System, Q/•/c. Dig., Federation Paint &• Varnish Production Clubs, 28, 466-75 (1956).

(4) Griffin, W. C., Emulsification, in Sagarin, E., Cosmetics: Science and Technology, Inter- science Publishers, New York, N.Y., 1957, pp. 998-1033.

(5) Becher, P., The effect of the nature of the emulsifying agent on emulsion inversion, J. Soc. Cosmetic Chemists, 9, 141-8 (1958).

(6) Ross, S., Chen, E. S., Becher, P., and Ranuto, H. J., Spreading coefficients and hydro- phile-lipophile balance of aqueous solutions of emulsifying agents, J. Phys. Chem., 63, 1681-3 (1959).

(7) Becher, P., Spreading, HLB, and emulsion stability, J. Soc. Cosmetic Chemists, 11, 325- 32 (1960).

(8) Greenwald, H. L., Brown, G. L., and Fineman, M. N., Determination of the hydrophile- lipophile character of surface-active agents and oils by a water titration, Anal. Chem., 28, 1693-7 (1956).

(9) Atlas Chemical Industries, Inc., The Atlas HLB System, pamphlet, 1963.