266 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The subject of performance of a soap or syndet-based shampoo in soft and hard water has been tossed around by both the cosmetic chemist and the chemical supplier to the cosmetic industry. The word shampoo im- plies a copious lathering or foaming of a liquid type preparation of cleansing the scalp and the hair. The successful shampoo is expected to perform in soft or hard waters, to rinse out easily, and leave a clean, nonirritating feeling to the scalp and the hair lustrous, soft and manageable. The cos- metic chemist attempts to formulate a shampoo to give these effects and perform under wide variations of normal conditions of use. The consumer usually judges the performance of a shampoo by its immediate and per- sistent lathering or fo.•ming action, by the number of applications required to give desirable lathering and whether it rinses out freely. If it lathers properly and rinses out freely, then reflection is made to other effects pleasing or displeasing to the consumer. Much dissatisfaction with shampoos arises from poor lathering perform- ance be it in soft or hard water. There may be little complaint with performance of the shampoo in soft water, but hard water eliminates many types from competition and with others in moderately hard water leave much to be desired. Perhaps, the foremost prerequisite then is that the shampoo preparation shall be designed to perform satisfactorily up to a given hardness to blanket the greatest potential market. The cosmetic chemist has relied on a combination of synthetic surfactants or soap plus a syndet to affect better performance in hard water areas. Fatty alkylolamides in combination with sodium lauryl sulfate or TEA soaps improved performance in moderately hard waters but above 150 p.p.m. hardness foam depression was still very evident unless, of course, higher concentrations were used. A very useful property of the alkylol- amides is their lime soap dispersing ability. This feature coupled with a chelating agent can be exploited to make soap-based shampoos very com- petitive with syndet shampoos. The chelating agent is to be responsible for the softening of the water and foam stability during the shampoo cycle and the alkylolamide for its lime dispersing action during the rinsing cycle. This combination in a potassium or TEA soap shampoo will produce excellent foaming at low concentration which is a very important feature toward gaining consumer's preference. Complete softening of the water is unnecessary in the case of syndet- based shampoos. The amount of the chelating agent to use should be based on lowering the hardness from a predetermined maximum to the optimum performance level for the syndet. This approach will enable the manufacturer to extend his product into market areas with hardness levels at 300 p.p.m. A look at sodium stearate demonstrates the foam stabilization action of EDTA. The calcium salt of stearic acid is quite insoluble in water.

ASPECTS OF CHEI,ATION IN COSMETIC PRODUCTS 100 200 7_00 -- •50-- 100- 50-- Mo/e Na•oeDTA O. ! • $od/•,m stearate o I I 20 60 100 140 180 220 260 Go. CO 3 HARDNESS, PPM Figure 3.--CaCOa vs. foam height. 267 Foaming of stearate or any soap solutions is pH dependent and a very sharp break in the standard foam curve occurs between 100 and 200 p.p.m. CaCOa when a 0.1 per cent solution of sodium stearate with the pH adjusted to 10.0 is investigated. Figure 3 shows the protective action of EDTA for such a dilute soap solution. At 0.5 mole EDTA to a mole of hardness, EDTA effected 84 per cent regeneration of the predicted foam height. At a mole to mole ratio 100 per cent regeneration was obtained. None of the dehydrated phosphates generated any foam at all even at mole ratios to hardness of 10 to 1. Since chelating agents are sold on a chelation performance toward CaCOa, one can easily calculate the required amount to add to any soap or