Cocamidopropyl betaine (CAPB) is an important surfactant used in personal care. However, it is only one of a series of possible alkyl groups that can be used to make betaines. There are two types of betaines: alkyl betaines and amido betaines.
Amido betaine products are mild, foaming amphoteric surfactants that complex with anionics. They are used extensively in shampoos, bubble baths and in other cleansing products. The structure of alkylamidopropyl betaine is show in Figure 1.
Amido betaines can be derived from a variety of natural oils or fatty acids, the choice of which can profoundly effect the performance in formulations.
The selection of the specific material used in formulations will affect foam, skin feel and viscosity of the product. Cetyl betaine is derived from cetyl dimethyl amine and is an alkyl betaine.
The betaines selected for a formulation can alter viscosity, foam and feel of formulated products and is a major way that a formulator may affect product performance. A selection of betaines and their properties is shown in Table 1.
The foam and viscosity of the different betaines were evaluated in a simple formulation of 60.5% w/w water (aqua), 32% w/w sodium lauryl sulfate and 7.5% w/w betaine. The results are described in the foam properties of Table 1 and illustrated in Figure 2.