Polyol esters

The most important polyol ester is the so-called glycerol monostearate (GMS). Generally, it is not a pure product but a mixture of mono- and diesters of stearic and palmitic acids. The main distinguishing feature is the content of monoester. Products with approx. 4O% monoester are obtained by direct esterification of stearic acid and glycerol. Products with approx. 6O% monoester are produced by glycerolysis of triglycerides with glycerol. The 9O% material can be obtained by molecular distillation but is seldom used in cosmetic formulations because the mono/diesters provide the best applicational properties.
GMS is poorly soluble in waler. However, as with the fatty alcohols, when combined with more hydrophilic emulsifiers, it is an excellent co-emulsifier
and becomes self-emulsifying. Typical combinations are :
• GMS plus potassium stearate (GMS self-emulsifying’)
• GMS plus sodium lauryl sulfate
• GMS plus ethoxylated fatty alcohols (‘GMS sell-emulsifying, acid stable’)
Other polyol esters used a co-emulsifiers are the sorbitan esters, especially the monostearate. These are obtained by dehydration of sorbitol to sorbitan followed by esterification with fatty acid. Such products are typically offered as pure products, and function as water-in-oil (W/O) emülsifiers. In oil-in- water formulations they are most often combined with ethoxylated products of the same family.