Ricardo C. Pasquali

Some considerations about the hydrophilic–lipophilic balance system

The methods and results obtained by Griffin et al. in the determination of the hydrophilic-lipophilic balance (HLB) values of non-ionic surfactants and of required HLB values of oil mixtures are reviewed in the present work. HLB values published by Griffin were compared with those obtained by calculations from theoretic chemical formulas. Griffin HLB values of polyoxyethylene alkyl ethers, polyoxyethylene monoesters and propylene glycol monoesters coincide with those obtained from such theoretical chemical formulations. These results demonstrate that, for these surfactants, Griffin did not experimentally obtain their HLB values, but instead calculated them from theoretic formulae. For the calculation of the HLB values of glycerol monostearate, sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters, Griffins assumptions were possibly based upon the mean saponification values of the ester and the acid of the fatty acid. It is concluded that the HLB values of non-ionic surfactants were not rigorously defined. Moreover, Griffin could not demonstrate the validity of the assumption that individual required HLB values can be added up to obtain the overall required HLB value of an oil mixture. The HLB and required HLB values published by Griffin should only be taken as approximate guidelines.

New Values of the Required Hydrophilic-Lipophilic Balance for Oil in Water Emulsions of Solid Fatty Acids and Alcohols Obtained from Solubility Parameter and Dielectric Constant Values

The goals of this articles are to find a correlation between the required HLB values and the solubility parameters of oils; find a more precise correlation between the required HLB values and the dielectric constant, than the one obtained by other authors; and to determine the required HLB values for o/w emulsions of solid fatty acids and alcohols from the values of the solubility parameters and dielectric constants, that could be more trustful than the ones obtained by the methodology proposed by Griffin. It was obtained lineal relation between required HLB and solubility parameter (r = 0.995). Also it was observed lineal relations between required HLB and dielectric constants or logarithm of the dielectric constant more precise than the one obtained by other authors.

Stability of Lipogels with Low Molecular Mass Gelators and Emollient Oils

The influence of preparation methods on stability of lipogels was studied. The objectives of this study were to evaluate the ability of different low molecular solid ingredients used as excipients in pharmaceutical and cosmetical products to form lipogels with emollient liquids of different polarities as well as to evaluate the stability of the lipogels obtained and the spreading ability of stable lipogels. The lipogels were prepared by heating the mix of oil and gelator a 100°C with two different forms of cooling: slow cooling of the without stirring and quick cooling with stirring. The stability tests were one year of storage at room temperature, centrifugation and three months at 40°C. None of the lipogels prepared with slow cooling and without stirring were stable in all stability tests. Eight of the formulations with quick cooling and stirring were stables in all stability tests: six with 12-hydroxystearic acid, one with hydrogenated castor oil, and one with beeswax as gelators. The lipogels with 12-hydroxystearic acid as gelator do not spread on skin or form clusters that spread after pressing with the fingers. The two lipogels with castor oil have good spreading ability on the skin.

The Calculus of HLB Values of Polyoxyethylene Fatty Acid Esters from Quality Control Data

In this article, we obtained equations that permit us to calculate the hydrophilic-lipophilic balance (HLB) value of polyoxyethylene esters from quality control data of the raw materials (fatty acids and polyethylene glycol) and the finished product (surfactant). These data include the acid value of the fatty acid, the hydroxyl value of the polyethylene glycol, and the hydroxyl value of the surfactant. These calculations permit us, moreover, to know the mean molecular masses of fatty acids, of polyethylene glycol, of monoester and diester, and the proportion of polyoxyethylene monoester and polyoxyethylene diester.

“True” Hydrophilic-Lipophilic Balance of Polyoxyethylene Fatty Acid Esters Nonionic Surfactants

This article proposes a set of equations that allow the calculation of the hydrophilic-lipophilic balance (HLB) value of polyoxyethylene esters from quality control data of the raw materials (fatty acids and polyethylene glycol) and the finished product (surfactant). The quality control data required include the acid value of the fatty acid, the hydroxyl value of the polyethylene glycol, and the hydroxyl value of the surfactant. Moreover, these calculations allow the determination of the mean relative molecular masses of the fatty acids, polyethylene glycol, monoesters, and diesters, and to calculate the proportion of polyoxyethylene monoester and polyoxyethylene diester. Models such as this would be of great utility for the rational design of emulsified products.

Letter to the Editor: The Molecular Distribution and HLB Value of Nonionic Polioxiethylenated Surfactants

In 1940, Flory deducted that the molecular distribution of ethylene oxide polymers, obtained by reaction of ethylene oxide with ethylene glycol, is represented by Poissons distribution law. This mathematical equation was subsequently used by other authors for calculating the fractions molars of the products of the reaction of ethylene oxide with alcohols and phenols, without taking into account to be used as quantity of units of ethylene oxide to x instead of x − 1. In this article, it is theoretically demonstrated that if the equation obtained by Flory is modified in this way, it gets that the hydrophilic-lipophilic balance of non ionic polioxiethylenated surfactants can be calculated from the mean number of molecules of ethylene oxide that reacts with one molecule of alcohol or phenol.