•50 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS with water and conduct electricity. For these purposes the emulsion chem- ist would under no circumstances use an oil-soluble surfactant. However, to make a water-in-oil emulsion, to couple water-soluble materials into an oil, or to make a dry-cleaning detergent, all of which are non-aqueous sys- tems, he would choose an oil-soluble surfactant. This relationship of behavior and water solubility that is followed by most experienced emulsion chemists is so inexact in its usual form that it is only of value as a basis of thinking. We have been successful in assigning nu- merical values to surfactants, thereby providing a system of classification that is related to their behavior and to their solubility in water. This method, called the HLB method from the term Hydrophile-Lipophile Bal- ance, is based on the premise that all surfactants combine hydrophilic and lipophilic groups in one molecule and that the proportion between the weight percentages of these two groups for non-ionic surfactants is an indication of the behavior that may be expected from that product. The HLB value is useful because it allows a prediction of the action that may be expected from a surfactant for example a low value, about 4, will be a water-in-oil emulsifier a high value, about 16, will be a solubilizer. What is referred to here is the type of behavior that can be expected, rather than the efficiency with which this will be accomplished. In our laboratory the behavior ofsurfactants in relationship to their hydro- philic nature was first recognized in emulsion studies. When two non-ionic emulsifiers, one hydrophilic and the other lipophilic, were mixed in varying ratios the efficiency of the blend as an emulsifier for a given oil went through a maximum. Using pairs of different surfactants to emulsify the same oil, it was apparent that this maximum occurred at the same weight percentage of hydrophilic substance in the surfactant blend. Essentially therefore, the HLB value is a function of the weight percentage of the hydrophilic portion of the molecule of a non-ionic surfactant. HLB values may be calculated for non-ionic surfactants or may be deter- mined experimentally. The experimental procedure is long and laborious and was described a few years ago [J. Soc. COSMETIC CHEM., 1,311-326 (1949)]. Formulas for calculating HLB values may be based on either analytical or composition data. For most polyhydric alcohol fatty acid esters ap- proximate values may be calculated with the formula HLB= 20(1 Wherein: S = saponification number of the ester A = acid number of the acid
HLB VALUES OF NON-IONIC SURFACTANTS zSx Examples: (A) Atmul 67© glyceryl monostearate (soap free) $ = saponification number, 161 A = acid number of fatty acid, 198 HLB = 20 (1- 16_1'• 198] = 3.8 (B) Tween 20©, polyoxyethylene sorbitan monolaurate $ = saponification number spec., 45.5 (mid-point) A = acid number of fatty acid, 276 HLB = 20 (1 -- 45.5'• = 16.7 276 ] Many fatty acid esters do not give good saponification number data for example, tall oil and rosin esters, beeswax esters, lanolin esters. For these a calculation may be based on the formula: E+P HLB - 5 Wherein: E = weight percentage of oxyethylene content P = weight percentage of polyhydric alcohol content (glycerol, sorbitol, etc.) Example: Atlas G-1441 polyoxyethylene sorbitol lanolin derivative E = weight percentage of oxyethylene content, 65.1 P = weight percentage of polyhydric alcohol content, 6.7 65.1 + 6.7 HLB- - 14 5 In products wherein only ethylene oxide is used as the hydrophilic portion and for fatty alcohol ethylene oxide condensation products, equation 2 may be simplified to E HLB - . Example: Myrj 49© polyoxyethylene stearate E = weight percentage of oxyethylene content, 76 HLB = 7• = 15 These formulas are satisfactory for non-ionic surfactants of many types. However, non-ionic surfactants containing propylene oxide, butylene oxide, nitrogen, sulfur, etc., exhibit behavior which has not been related to com- position. In addition, the HLB values of ionic surfactants do not follow a weight percentage basis because even though the hydrophilic portion is low in molecular weight the fact that it ionizes lends extra emphasis to that portion and therefore makes the product more hydrophilic. For these products, the experimental method must be used. © Reg. U.S. Pat. Off., Atlas Powder Company.
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•50 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS with water and conduct electricity. For these purposes the emulsion chem- ist would under no circumstances use an oil-soluble surfactant. However, to make a water-in-oil emulsion, to couple water-soluble materials into an oil, or to make a dry-cleaning detergent, all of which are non-aqueous sys- tems, he would choose an oil-soluble surfactant. This relationship of behavior and water solubility that is followed by most experienced emulsion chemists is so inexact in its usual form that it is only of value as a basis of thinking. We have been successful in assigning nu- merical values to surfactants, thereby providing a system of classification that is related to their behavior and to their solubility in water. This method, called the HLB method from the term Hydrophile-Lipophile Bal- ance, is based on the premise that all surfactants combine hydrophilic and lipophilic groups in one molecule and that the proportion between the weight percentages of these two groups for non-ionic surfactants is an indication of the behavior that may be expected from that product. The HLB value is useful because it allows a prediction of the action that may be expected from a surfactant for example a low value, about 4, will be a water-in-oil emulsifier a high value, about 16, will be a solubilizer. What is referred to here is the type of behavior that can be expected, rather than the efficiency with which this will be accomplished. In our laboratory the behavior ofsurfactants in relationship to their hydro- philic nature was first recognized in emulsion studies. When two non-ionic emulsifiers, one hydrophilic and the other lipophilic, were mixed in varying ratios the efficiency of the blend as an emulsifier for a given oil went through a maximum. Using pairs of different surfactants to emulsify the same oil, it was apparent that this maximum occurred at the same weight percentage of hydrophilic substance in the surfactant blend. Essentially therefore, the HLB value is a function of the weight percentage of the hydrophilic portion of the molecule of a non-ionic surfactant. HLB values may be calculated for non-ionic surfactants or may be deter- mined experimentally. The experimental procedure is long and laborious and was described a few years ago [J. Soc. COSMETIC CHEM., 1,311-326 (1949)]. Formulas for calculating HLB values may be based on either analytical or composition data. For most polyhydric alcohol fatty acid esters ap- proximate values may be calculated with the formula HLB= 20(1 Wherein: S = saponification number of the ester A = acid number of the acid
HLB VALUES OF NON-IONIC SURFACTANTS zSx Examples: (A) Atmul 67© glyceryl monostearate (soap free) $ = saponification number, 161 A = acid number of fatty acid, 198 HLB = 20 (1- 16_1'• 198] = 3.8 (B) Tween 20©, polyoxyethylene sorbitan monolaurate $ = saponification number spec., 45.5 (mid-point) A = acid number of fatty acid, 276 HLB = 20 (1 -- 45.5'• = 16.7 276 ] Many fatty acid esters do not give good saponification number data for example, tall oil and rosin esters, beeswax esters, lanolin esters. For these a calculation may be based on the formula: E+P HLB - 5 Wherein: E = weight percentage of oxyethylene content P = weight percentage of polyhydric alcohol content (glycerol, sorbitol, etc.) Example: Atlas G-1441 polyoxyethylene sorbitol lanolin derivative E = weight percentage of oxyethylene content, 65.1 P = weight percentage of polyhydric alcohol content, 6.7 65.1 + 6.7 HLB- - 14 5 In products wherein only ethylene oxide is used as the hydrophilic portion and for fatty alcohol ethylene oxide condensation products, equation 2 may be simplified to E HLB - . Example: Myrj 49© polyoxyethylene stearate E = weight percentage of oxyethylene content, 76 HLB = 7• = 15 These formulas are satisfactory for non-ionic surfactants of many types. However, non-ionic surfactants containing propylene oxide, butylene oxide, nitrogen, sulfur, etc., exhibit behavior which has not been related to com- position. In addition, the HLB values of ionic surfactants do not follow a weight percentage basis because even though the hydrophilic portion is low in molecular weight the fact that it ionizes lends extra emphasis to that portion and therefore makes the product more hydrophilic. For these products, the experimental method must be used. © Reg. U.S. Pat. Off., Atlas Powder Company.

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