Formulating Twoinone Shampoos

The essence of the two-in-one shampoo technology is to incorporate the appropriate conditioning ingredients into a shampoo base to achieve both cleansing and t conditioning of hair in one step from a single product. For the conditioning agent to work properly in a shampoo formula, it must be not only substantive to the hair but strong enough to survive the accompanying detergent actions and the subsequent water rinse. Equally important, it should have minimal interference with cleansing actions or lathering characteristics. These were challenges that confronted earlier chemists [25-28]. But thanks to the stream of new or improved ingredients, a clear understanding of the properties and interactions of these materials, formulation strategies have evolved over the years and in fact have become more routine. The advances of this technology are discussed next.

3.1 The Cationic/Amphoteric Combinations

A typical approach to formulating one-step conditioning shampoo in the late 1960s and early 1970s was to incorporate a hair conditioning agent into a shampoo base consisting primarily of amphoteric surfactants. A number of such agents were reported, including protein hydrolysate [29] and mineral oil [30]. The materials most frequently used, however, were monomeric quaternary ammonium compounds [33,34] or quaternized polymers [31,32]. These are cationic materials that contain quaternary nitrogen to give them unusual substantivity to the hair surface [35,36]. The quaternary ammonium compounds, especially those with a long alkyl chain (14-22 carbons), have been known to be able to impart some unique properties [37-39] to the hair and have been widely used in hair rinse conditioners. They have been claimed to make the hair feel soft and smooth, easy to comb, and less prone to static buildup. Taking advantage of these ingredients, formulators had some success in formulating one-step shampoo by utilizing quaternary compounds in combinations with amphoteric surfactants. A typical example of such a formulations is shown in Table 1. The choice of amphoteric surfactants was primarily dictated by concerns that cationic and anionic materials would not be compatible, and that either cleansing or conditioning would be severely compromised.

Table 1 Shampoo Formulation with Amphoteric/Cationic Combination

Ingredients Amount (wt %)

Cocoamphodiacetate 20.00

Coamidopropyl hydroxysultaine 12.00

Glycerol stearate 1.00

Lauramide DEA 3.00

Hydrolyzed protein 2.00

Polyquaternium-27 2.40

Deionized water As needed to make 100

This novel concept of a one-step shampoo was well received. It generated a lot of consumer interest and had considerable impact in the marketplace, with Milk Plus Six (from Revlon) as the prime example. The success was short-lived, however, because of some inherent shortcomings. It became increasingly apparent that the hair cleansing action was not sufficient, and there was slow buildup of residues on the hair. On repeated usage, these shampoos would "over condition" the hair, leaving it limp, weighed down, and lacking in body. Again, formulators began refocusing their efforts to develop a one-step shampoo using anionic surfactants as the primary cleaning agents. The amphoteric/cationic combinations alone are rarely used these days. Practically all the two-in-one shampoo formulations contain some anionic surfactants.

3.2 The Dilution-Deposit Technology

An important milestone for the two-in-one shampoo takes advantage of hair conditioning attributes of some cationic polymers and some unusual mixture properties of cationic polymers and anionic surfactant. Cationic polymer and anionic surfactant paired in a single system would normally be incompatible, producing an insoluble complex that would precipitate. It was found, however, that at some ratio of surfactant to cationic polymer, when the surfactant is in excess, the precipitate could be redissolved to form a clear solution. What is important is the concentration of the anionic surfactant. When the anionic concentration is above its cmc, the complex is solubilized to form a stable emulsion. But if the anionic concentration is brought below its cmc, the complex will become insoluble and precipitate. This phenomenon was first observed by some researchers who quickly recognized its implications as a useful "trigger mechanism" to deliver conditioning from shampoo formulated with anionic surfactant. The idea was that when the cationic and anionic surfactant are formulated appropriately, the complex should stay dissolved in the shampoo but precipitate onto the hair surface when diluted with water upon rinsing. This discovery spurted a flurry of research activities [30,41-46] and patent disclosures [47-51]. Indeed, this technology has evolved into a major strategy to formulate two-in-one shampoos. Some typical formulations are shown in Tables 2 and 3.

3.3 The Silicone Advantages

Another important advance in the two-in-one technology was the utility of silicone polymers as hair conditioning agents in a shampoo. The appeal of silicone was the rather unique surface properties that cationic surfactants and quaternized polymers did not have. Silicones were found to be able to impart certain dry conditioning attributes to the hair that the polymer-surfactant complex cannot deliver as effectively. The molecular structures and flexibility [54] of some silicone polymers are believed to promote unusual lubricity of the hair and to make the hair feel

Table 2 Shampoo Formulation Using Cationic Polymer with Anionic Surfactants

Ingredients Amount (wt %)

TEA lauryl sulfate (40% active) 38.00

Lauramide DEA 3.00

Hydroxyethylcellulose 1.00

Polyquaternium-11 2.00

Hydrolyzed protein 2.00

Perfume/preservatives As needed

Deionized water As needed to make 100

Table 3 Shampoo Formulation Using Cationic Polymer with Anionic Surfactants

Ingredients Amount (wt %)

Cocoamphodiacetate/disodium 18.50

cocamido sulfosuccinate

TEA lauryl sulfate (40% active) 18.50

Propylene glycol 2.00

Lauramide DEA 4.00

Polyquaternium-10 0.70

Citric acid 0.50

Preservative/fragrance As needed Distilled water As needed to make 100

soft and smooth. The low surface tension and high refractive index of these polymers allow them to improve hair shine and luster [55]. In fact, numerous patent disclosures dating back to the 1960s claim the uses of silicon polymers as effective conditioning agents for shampoo [56-63]. Silicone polymers, however, are highly hydrophobic, and have limited solubility in water or other common organic solvents. The challenge of having silicones in shampoo formulations was not only to keep the various ingredients properly suspended but to ensure that they remained stable over the shelf life of the product. The answers to this challenge were revealed by the patents issued to Procter & Gamble [61,62]. In these patents, :f the company has claimed a unique formulation technology and manufacturing process for a shampoo composition containing nonvolatile silicones, anionic surfactants, and other ingredients to achieve a stable and emulsion; moreover, the sil- J

t icone is said to have minimal effect on shampoo lather and cleansing. It works by depositing on hair via dilution upon rinsing. This technology became the basis of Pert Plus and other two-in-one shampoos across P&G's product line. Subsequently, Vidal Sassoon, Pantene, Ivory, and Head and Shoulders all have taken this major technological advance and used it to improve product performance across the board on a large front. In response to this development, other shampoo manufacturers have also mounted major efforts to match or surpass this patented technology, resulting in a flurry of product launches [64], as well as research and patent activities [65-71]. Some typical examples of two-in-one shampoos formulated with silicons are shown in Tables 4 and 5.

3.4 Using Both Cationic Polymers and Silicone

As the two-in-one technology has further evolved, formulators are beginning to use a blend of cationic polymers and silicones as dual conditioner in two-in-one shampoos. One advantage of this approach is that the two conditioning agents are complementary. While the polymer-surfactant complex gives the hair excellent wet conditioning effects, silicones provide superior dry benefits, imparting unusual silkiness and softness to the hair. Another advantage is that this approach offers a considerable degree of formulation flexibility. The combination would avoid using excessive high concentration of either the cationic polymers or sili-cones. Too much polymer-surfactant complex would have the potential to cause a

Table 4 Shampoo Formulation Using Silicone Polymer with Anionic Surfactants

Ingredients Amount (wt %)

Ammonium lauryl sulfate (40% active) 16.00

Xanthan gum 0.75

Cocamide MEA 2.00

Dimethicone 1.00

Cetearyl alcohol 1.00

Silicone gum 1.00

Fragrance 1.00

Sodium chloride 0.10

Preservatives 0.03 £

Caustic soda (50% active) 0.01 s

Ethylene glycol 0.75

Dye solution 0.65 Water (double reverse osmosis) As needed to make 100

Table 5 Shampoo Formulation Using Silicone Polymer with Anionic Surfactants

Ingredients

Ammonium lauryl sulfate (40% active)

Ammonium lauryl-3-sulfate

Ammonium xylenesulfonate

Cetearyl alcohol

Glycol distearate

Cocamide MEA

Xanthan gum

Dimethicone

Silicone gum

Tricetyl ammonium chloride

Fragrance/color

Water

16.00 4.00 2.20 1.00 0.75 1.00 0.75 1.00 1.00 1.00 As needed As needed to make 100

slow buildup of residues. Too much silicone in a shampoo would severely affect the lathering characteristics. Thus, this approach has become a useful tool to formulate a two-in-one product that is able to clean hair adequately and is also able to deliver the best of hair conditioning characteristics. The key is to recognize the appropriate combinations of cationic polymer, silicone, anionic surfactants, and amphoteric surfactants. In fact, a recent survey of 10 different major commercial brands shows that the majority of two-in-one shampoos are now formulated almost exclusively using both cationic polymers and silicones as conditioning agents. The essential ingredients of these brands are summarized in Table 6.

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