RUSSELL D. COX
Stephenson Speciality Chemicals, Brookfoot House, Low Lane, Horsforth, Leeds, West Yorkshire, LS18 5PU, United Kingdom

Abstract

The use of emulsions is widespread in the personal care industry. This two part article provides an insight into the chemistry employed in the development and manufacture of emulsions. The discussion covers useful mathematical tools that can be used in the selection of emulsifiers.

HYDROPHILIC LIPOPHILLIC BALANCE
In 1949 Griffin (1, 2) proposed a method for classification of non-ionic emulsifiers to assist in their selection for producing stable emulsions. His method known as the Hydrophilic Lipophilic Balance is usually abbreviated to HLB (see Table 1).

The HLB value of an emulsifier can be determined by comparing the relative content of the hydrophilic region of the molecule to the molecule as a whole. The formula is as follows:


Where:
Mh = molecular weight of the hydrophilic component of the molecule
M = total molecular weight.

From an experimental standpoint, when referring to ester-derived emulsifiers, the HLB can be determined using the following formula and data that can be measured relatively easily in the laboratory:


Where:
Av = Acid value
Sv = Saponifi ... ...