GB2197875A - Surfactant composition for body application - Google Patents

Abstract

A surfactant composition comprises a isethionate surfactant and an amine oxide surfactant. Good foaming properties, compatibility and low irritancy are observed. Solubility of isethionate surfactant is increased by adding the amine oxide. The compositions are suitable for shampoos, shower gels, liquid soaps and skin care products. The mixture possesses a lower Critical Micelle Concentration than the individual components.

Description

SURFACTANT COMPOSITION The present invention relates to surfactant compositions which are useful in various formulations, particularly in cosmetic formulations.

Most mild cosmetic formulations are based on ether sulphates. It has been found that such formulations contain undesirable amounts of by-products such as dioxane or ethylene oxide.

The presence of even a small amount of dioxane is undesirable and is being discouraged and, in the future, may even be prohibited by government regulations due to the recently recognised carcinogenic properties associated with this chemical.

Irritation of the eyes or skin is another characteristic which is detrimental for the commercial acceptance of a cosmetic formulation.

Therefore, it has been desirable for some time to provide new surfactants, or surfactant compositions, which can be used in cosmetic formulations and which avoid the above mentioned deficiencies.

It is known to use long chain alkyl isethionates derivatives as surfactants in formulations such as, in particular, cosmetic soap-bar formulations. Some applications are described in US Patent specifications 2894912, 2972582, 3248333 and 3687855.

It has now been found that surprisingly, a surfactant composition having a useful combination of properties is obtained by mixing an isethionate surfactant with a long chain alkyl amine oxide.

It has been found that not only is the undesirable dioxane by-product absent from such a composition but also'the combination of the specified two surfactants results in better foaming properties and lower irritation and also good compatibility with other surfactants of the anionic, cationic or nonionic type.

According to the present invention there is provided a surfactant composition comprising (a) at least one isethionate compound of the formula (I) R - COO - CH2 - CH2 - SO - M (I) (b) at least one amine oxide of the formula (II)

wherein: R is a hydrophobic radical capable of imparting surface active properties to the molecule; R is a hydrophobic radical capable of imparting surface active properties to the molecule; R2 and R3 are, independently, a hydrogen atom or a lower alkyl group; and M is an alkali metal ion or an ammonium ion.

The groups R and R are typically hydrocarbyl groups, particularly hydrocarbyl groups containing 5 to 25 carbon atoms and especially saturated alkyl groups containing 7 to 17 carbon atoms.

It will be appreciated that the groups R and R may be the same or different and, in general, the groups R and R1 are different. The groups R and R1 may be a mixture of groups, for example a mixture of alkyl groups containing from 11 to 15 carbon atoms. The group R is typically a straight chain saturated alkyl group or a mixture of such groups. The group R1 is typically a mixture of straight chain and branched chain saturated alkyl groups. The groups R and R may be derived from naturally occurring products, for example the group R may be part of a cocyl group in which R is a mixture of straight chain saturated alkyl groups having, on average, 11 carbon atoms.

It is preferred that the ratio of the isethionate to the amine oxide varies from 10:1 to 1:10, by weight, especially from 10:1 to 1:1, and particularly from 3:1 to 2:1.

The group M is preferably a sodium cation or a quaternary ammonium group.

A hydrocarbyl group as used herein means a residue obtained by removing a hydrogen atom from a hydrocarbon compound and an aliphatic group as used herein means a residue obtained by removing a hydrogen atom from a saturated or unsaturated, straight, branched or cyclic aliphatic hydrocarbon.

A suitable isethionate for use as component (a) of the surfactant composition is sodium cocoyl isethionate which is a commercially available material in which the group R is a mixture of straight chain alkyl groups containing from 7 to 17 carbon atoms and having, on average, 11 car-bon atoms. This material will hereafter be referred to as sodium cocoyl isethionate.

In the amine oxide which is component (b) of the surfactant composition, the group R is preferably a C11-C13 alkyl group or a C13-C15 alkyl group. A suitable amine oxide is a commercially available dimethyl C13-Cl5 alkyl amine oxide in which the alkyl groups are a mixture of straight chain and branched alkyl groups.

This material will hereafter be referred to as the "dimethyl mixed alkyl amine oxide". When taken alone such amine oxide compounds are generally solid at room temperature or are in the form of thick pastes. Other suitable amine oxide compounds include those derived from synthetic long alkyl amines wherein the group R1 is a mixture of C9-C11, C1 1-C13 or C13-C15 alkyl groups. Alternatively the amine oxide can be derived from natural amines in which the group R is a mixture of alkyl groups containing from 10 to 18 carbon atoms.

The surfactant composition of the present invention is conveniently prepared by simply mixing components I and II in water.

The order of mixing is not critical but it is generally preferred to mix the amine oxide with water and then add the isethionate and continue mixing. Once the mixing has been completed the water may optionally be partially or totally removed. Mixing of components I and II in water is preferably effected at an elevated temperature, a preferred temperature being from 400 up to 800C.

The active ingredients, that is components (a) and (b), may be present in water in a concentration of up to about 50% and typically of up to 35%, by weight of the mixture of (a) and (b).

The surfactant compositions of the present invention can be incorporated into a range of cosmetic end-products and, in such cosmetic end-products, the surfactant compositions are present in a concentration range of from 1 to 25%, and typically from 7 to 20%, by weight. The surfactant compositions are storage stable and soluble in water in a large range of proportions. The aqueous mixtures are clear, flowable and pumpable liquids. The viscosity of the aqueous mixtures will vary from 10,000 to 50,000 mPa sec, and is typically about 20,000 mPa sec. Storage stability is maintained even after centrifuging, for example at 1500 rpm (9000 g) for 3 hours.

The amine oxide acts as a processing aid for the isethionate surfactant. Good handling and solubility are achieved. Thus, sodium cocoyl isethionate is soluble in water at a maximum concentration of 0.01% by weight, at 20-25"C. In contrast, up to 20% by weight of this isethionate is soluble in water in the presence of 8% by weight of the dimethyl mixed alkyl amine oxide.

Other ingredients, in particular other surfactants, may be used in conjunction with the surfactant composition of the present invention in products containing the surfactant composition. Other ingredients which may be used include, for example, lauryl ester sulphate, alkyl succinates, polysorbates, protein fatty acid condensate products, ammonium lauryl ether, lauryl amido ether sulphate, sodium lauryl myristyl ether (3EO) sulphate, and alkyl benzene sodium sulphonate. The compatibility of the surfactant compositions of the present Invention with other surfactants is surprisingly good. In contrast with ether sulphate, cationic surfactants such as ammonium derivatives are compatible with the surfactant compositions of the present invention.

litioxidants, colours, perfumes and the other usual ingredients or additives well-known in cosmetics may also be used with the surfactant compositions of the present invention.

The surfactant composition of the present invention provides good foaming properties associated with low irritation and the absence of dioxane.

The foaming properties have been investigated using the well-known Ross-Miles test with 0.5% active material in water. In each case foaming of the surfactant composition in accordance with the present invention appears to be better than that observed with the separate ingredients.

Other experiments have shown that the CMC (Critical Micellar Concentration) is smaller with the surfactant composition of the present invention.

CMC has been correlated with the skin irritancy of surfactants used in cosmetics. Dialysis experiments have demonstrated that only monomers penetrate membranes and micelles do not penetrate membranes or do so only very slowly. Thus, a lower CMC has the consequence of a lower monomer concentration, and hence the surfactant compositions of the present invention appear to be potentially of low skin irritance. These surfactant compositions are therefore particularly suitable for applications in skin-care product, shampoos or bath products.

A desired viscosity can be achieved by the known addition of sodium chloride. In comparison with other surfactants which can be used for the same purpose, for example ether sulphates, a lower concentration of sodium chloride is generally needed in order to obtain the same thickening effect. For some systems containing a surfactant composition in accordance with the present invention, a sodium chloride concentration of 1% by weight will have the same effect as a sodium chloride concentration of 6% by weight in standard ether sulphate formulations.

Formulations incorporating the surfactant compositions of the present invention are storage stable.

The surfactant compositions of the present invention may be used to product cosmetic end-products and may also be advantageously used for the preparation of pharmaceutical or industrial preparations.

The present invention is illustrated by the following non-limiting examples.

Examples 1 to 3 Three compositions in accordance with the present invention were prepared by mixing together an amine oxide and water, heating the mixture to about 60"C, adding an isethionate and continuing to mix until the isethionate had dissolved.

The compositions of the mixtures obtained are set out in Table 1.

Table 1

Surfactant Composition (b) (a) 1 2 3 SCI 20.0 25.5 16.5 DAAO 8.5 3.0 12.0 Notes to Table 1 (a) SCI is sodium cocoyl isethionate in which the group R is a mixture of straight chain alkyl groups containing from 7 to 17 carbon atoms and having, on average, 11 carbon atoms.

TAAD Is dimethyl alkyl amine oxide in which the alkyl group is a mixture of straight chain and branched chain saturated alkyl groups containing 13 to 15 carbon atoms.

(b) The compositions are given as parts by weight.

The compositions of Examples 1 to 3 were subjected to the Ross-Miles test using 0.5% e active material. For compazative purposes a number of commercially available surfactants were tested under the same conditions. The results obtained are set out in Figures 1 and 2 wherein Figure 1 shows the foam higher (in mm) using the surfactants in demineralised water; and Figure 2 shows the foam height (in mm) using the surfactants in water of hardness of 342 ppm.

In Figures 1 and 2 the surfactants are indicated by letters or numbers which have the following significance: A is a cocoamidopropyl betaine CTFA available from Th.Goldsmidt as Tegobetain L7.

B is an ether sulphate available from Henkel as Texapon N40.

C is an ether sulphate available from Imperial Chemical Industries PLC as Synperonic 3S 70.

D is a surfactant available from Imperial Chemical Industries PLC as Synperonic 2S 70.

E- is DAAO as defined in Note (a) to Table 1.

1 is composition 1 of Table 1.

2 is composition 2 of Table 1.

3 is composition 3 of Table 1.

Example 4 The Critical Micellar Concentration (CMC) of a number of surfactants, and of a surfactant composition in accordance with the present invention, were determined using standard methods. The results obtained are set out in Table 2.

Table 2

Surfactant CMC (a) 8/1 mmoljl DAAO 0.0126 0.049 SC 0.063 0,183 DAAO/SCI mixture (30:70 by weight) 0.01 0.031 protein-fatty acid condensate - 0.04 sodium sulphosuccinic acid ester - 0.21 sodium lauryl sulphate - 7.2 sodium lauryl ether (2EO) sulphate - 1.5 Example 5 Adjustments of viscosity were carried out by the addition of other surfactants, in some cases in the presence of sodium chloride, to an aqueous composition containing the SCI/DAAO mixture of Example 1. Results are as indicated below.

System 1 A 20 40 60 80 SCI/DAAO 80 60 40 20 Viscosity (mPa.sec) 1160 1660 99600 664 System 2 A 20 40 60 80 B 80 60 40 20 Viscosity (mPa.sec) 144420 94620 161020 1245 System 3 F 20 40 60 80 SCI/DAAO 80 60 40 20 ±3% NaCl mPa.sec 2500 54000 16600 2500 + 7% NaCl mPa.sec 1300 2700 76000 21000 A is surfactant A as defined for Figures 1 and 2.

B is surfactant B as defined for Figures 1 and 2.

SCI/DAAO is the surfactant composition 1 of Table 1.

F is a disodium sulphosuccinate fatty acid obtainable from Schering as Ruwopol SBFA 30.

Claims (11)

1. A surfactant composition comprising (a) at least one isethionate compound of the formula (I) R - COO - CH - CH2 - SO - M (I) and (b) at least one amine oxide of the formula (II)

wherein: R is a hydrophobic radical capable of imparting surface active properties to the molecule; R is a hydrophobic radical capable of imparting surface active properties to the molecule; 3 R2 and R3 are, independently, a hydrogen atom or a lower alkyl group; and M is an alkali metal ion or an ammonium ion.

2. A composition as claimed in claim 1 wherein R and R1 are, independently, hydrocarbyl groups containing 5 to 25 carbon atoms.

3. A composition as claimed in either claim 1 or claim 2 wherein R and R1 are, independently, a mixture of groups.

4. A composition as claimed in either claim 2 or claim 3 wherein R is a straight chain saturated alkyl group of 7 to 17 carbon atoms or is a mixture of such straight chain saturated alkyl groups.

5. A composition as claimed in any one of claims 1 to 4 wherein R1 is a mixture of straight chain and branched chain saturated alkyl groups and R and R3 are both methyl groups.

6. A composition as claimed in any one of claims 1 to 5 wherein ratio, by weight, of the isethionate to the amine oxide varies from 10:1 to 1:1.

7. A composition as claimed in claim 6 wherein the ratio, by weight, of the isethionate to the amine oxide varies from 3:1 to 2:1.

8. A composition as claimed in any one of claims 1 to 7 wherein M is a sodium cation or a quaternary ammonium group.

9. A surfactant composition substantially as hereinbefore described with reference to the Examples.

10. An aqueous cosmetic composition containing a surfactant composition as claimed in any one of claims 1 to 9.

11. An aqueous cosmetic composition as claimed in claim 10 wherein the concentration of surfactants is between 5 and 45 per cent by weight.