Tony O’Lenick asks Bob Coots, PhD, of Colonial Chemical Inc., "What is the difference between cocamide DEA, MEA or DIPA when used in shampoos?" Following is Coots's response.
Chemically, alkanolamides are the reaction product of an alkanolamine such as monoethanolamine (MEA), diethanolamine (DEA) or diisopropanolamine (DIPA) and a fatty material such as triglyceride, acid or methyl ester. Their general structures can be represented as:
R-C(O)-NH-CH2CH2OH Cocamide MEA
R-C(O)-N-(CH2CH2OH)2 Cocamide DEA
R-C(O)-NH-CH2CH(CH3)OH Cocamide DIPA
Alkanolamides are ubiquitous and are added to many cosmetic formulations to affect viscosity and foam properties. The effect of the amine portion of the molecule is addressed here.
Alkanolamides are used to shift the salt curve of a formulation to the left, resulting in a high formulation viscosity with less sodium chloride. Formulation examples using the aforementioned alkanolamides are shown in Table 1. Sodium chloride was then added to the formulations in Table 1 and their viscosities were measured (see Table 2).
Figure 1 illustrates that the peak viscosity has some variation but most importantly, that the salt curve is shifted to the left, meaning it requires less salt to achieve the maximum viscosity.
Table 3 shows the sodium choride levels used to achieve maximum viscosity using alkanolamines.