WO2004104150A1

WO2004104150A1 - Foam-enhancing agent for surfactant mixtures

Info

Publication number: WO2004104150A1
Application number: PCT/EP2004/005404
Authority: WO
Inventors: Horst Denzer; Marco Michaelsen; Hamke Meijer; Hiroshi Abe
Original assignee: Kao Chemicals Gmbh
Priority date: 2003-05-21
Filing date: 2004-05-19
Publication date: 2004-12-02
Also published as: WO2004104151A1; EP1629074A1; EP1675934A1; EP1479754A1

Abstract

The invention relates to high-foaming surfactant mixtures containing alkyl ether carboxylates derived from alkanols having 6 to 22 carbon atoms and some particular non-ionic surfactants, and to the use of these mixtures as foam-enhancing agent or foam booster for surfactant mixtures. In particular, it provides an aqueous composition comprising: a) a specific alkyl ether carboxylate derived from alkanols having 6 to 22 carbon atoms; and b) one or more compounds of the following formula (I): wherein R' represents H or CH3; each m, n, and 1 independently represent a number from 0 to 7, the sum of m, n and 1 being in the range of 1 to 15, and where Bl, B2, and B3 independently represent H or an acyl group having 6 to 22 carbon atoms the weight ratio of component (a) to component (b) being in the range of 4:1 to 1:10.

Description

FOAM-ENHANCING AGENT FOR SURFACTANT MIXTURES

DESCRIPTION

Technical field

The invention relates to high-foaming surfactant mixtures containing alkyl ether carboxylates derived from alkanols having 6 to 22 carbon atoms and some particular non- ionic surfactants, and to the use of these mixtures as foam- enhancing agent or foam booster for surfactant mixtures ..

Prior Art

In a number of surfactant applications, consumers are looking for a high foaming capacity. For example, a shampoo that does not produce enough creamy, stable foam during shampooing has no chance of success on the market. The same applies to manual dishwashing detergents, even though a direct connection between the foaming capacity and the cleaning performance cannot be established at all in many cases .

Hence, besides performance requirements, such as cleaning performance and dermatological compatibility, the foaming behaviour is a further important product feature. However, not all surfactant mixtures which perform satisfactorily and are economical in use show the required foaming behaviour.

The main foaming characteristics of the surfactant formulations that determine their application in areas like personal and house-hold care, . washing, food industry, fire fighting, mineral flotation, and many others are: foaming ability, foam stability (foam remaining after certain period at rest) , foam quantity (associated with good cleaning effect) , creaminess of the foam (associated with conditioning effect) , foam density, texture of the foam and foam speed (foam produced after a very short period of time) . Insufficient foaming performance can thus for example materialize in an insufficient foaming power or in an insufficient foam stability. In the one case, the basic foam has sufficient height, but it collapses rapidly. In the other case, the exact opposite occurs, i.e. although the initial foaming height is comparably low, the foam remains stable for a long time. Moreover, it is desirable that the foam is obtained quickly upon use (e.g. after a few seconds). Furthermore, the foam must tolerate hard water and the presence of oil.

The number of surfactant combinations that meet this complex requirement profile tends to be small which explains why the same formulations are always found on the market.

One way of overcoming this problem would be to provide surfactant formulations with additives, so-called foam boosters or foam-enhancing agents, which favourably influence the foam properties of the mixtures.

For example, fatty acid alkanolamides can be used as foam boosters, but unfortunately they have the disadvantage that they are suspected of containing traces of nitrosamines which is totally inappropriate for applications where the preparations come into contact with the human skin.

There are several patents and patent applications describing detergent compositions having good foaming properties. For example, the Japanese patent application JP- A-2001-115187 describing a detergent composition comprising (a) an ether carboxylic acid-based surfactant represented by the formula:

Rι-Z-(AO)_n-Y-COOX wherein Ri is an optionally hydroxyl group- containing 5-21C alkyl or alkenyl group; Z is 0 or CONH;

A is a 2C or 3C alkylene group;

X is H, an alkali metal, an alkaline earth metal, ammonium, a mono-, di- or trialkanol ammonium or a basic amino acid having a total carbon number of 1- 22;

Y is a 1-3C alkylene group; and n is a number of 2-15; and (b) a glyceryl ether • bearing a 4-12C alkyl or alkenyl group Said detergent compositions are described to be low irritating to the skin, exhibiting good foaming properties, and excellent in moist feeling after rinsing and having low- temperature stability.

US 6 423 678 Bl describes a liquid detergent- composition comprising

(a) 1-90 wt.-% of a main surfactant that includes one or more anionic surfactants; and,

(b) 1-40 wt.-% of a hydrotrope, the hydrotrope consisting essentially of 90-100 wt.-% of a mixture of: i. a peaked ethoxylated alcohol where the alcohol has from about 6 carbon atoms to about 12 carbon atoms and is ethoxylated with an average ethoxylation degree of 3-9, being preferred a peaked C8 alcohol having an average of 7 moles of ethylene oxide; and ii. a polyethylene glycol ether of glycerin having an average ethoxylation degree of 2-60 , being preferred Glycereth-26. It is described that said hydrotrope provides an increased foam generation. As typical anionic surfactant, carboxylated alcohol ethoxylates are mentioned, among other anionic surfactants. However, it is stated that preferred anionic surfactants include those having at least one sulfur constituent.

Finally, reference is made to EP-B-0580263. This patent relates to the provision of pumpable, highly concentrated (having^' a solid content of at least 45 wt.-%) liquid aqueous solutions of salts of alkyl ether carboxylic acids derived from alkanols having at least 10 carbon atoms, additionally containing ethoxylated, or ethoxylated and carboxymethylated, products or mixtures thereof, derived from polyhydric alcohols, the degree of ethoxylation of those products being at least 0.5. The ethoxylated, and/or ethoxylated and carboxymethylated products are contained in an amount of at least 1 %, in particular 2 to '25 %, relative to the total amount of solids of ether carboxylic acid and ethoxylated and/or ethoxylated and carboxymethylated products. EP-B- 0580263 fails to address the foaming properties of these surfactant mixtures.

Summary of the invention

Accordingly, the complex problem addressed by the present invention is to provide surface-active preparations which do not show the above-mentioned disadvantages. In particular, the object of the invention is to find foam- enhancing agents that improve different foaming characteristics' such as the basic foam, the foam speed, the foam stability, etc., of a large number of surfactants, even in the presence of hard water and oil, which are the most usual conditions for consumers.

In order to solve this problem, the present invention provides an aqueous composition comprising

(a) an alkyl ether carboxylate of the following formula II:

Formula II:

R-0-(CH₂CH₂0)_n-CH₂COO- M⁺ wherein

R is an alkyl residue having 6 to 22 carbon atoms; n has a value in the range of 2 to 10, preferably 2.5 to 7; and M⁺ is an appropriate cation selected from the group consisting of an alkali metal, an alkaline earth metal, ammonium, an alkylammonium, an alkanolammonium and a glucammonium; and

(b) a mixture of compounds of the following formula (I) :

Formula I:

R'

CH₂-0-(CH₂CHO)_m-B.,

R' I CH-0-(CH₂CHO)_n-B₂

R' I CH₂-0-(CH₂CHO)_rB₃

wherein

R' represents H or CH₃; each m, n, and 1 independently represent a number from 0 to 4 , the sum of m, n and 1 being in the range of 1 to 4, and said mixtures comprising (i) compounds represented by formula (I) , where one of Bl, B2 and B3 represents an acyl group having 6 to 22 carbon atoms, the remainder representing H; (ii) compounds represented by formula (I) , where two of Bl, B2 and B3, independently, represent an acyl group having 6 to 22 carbon atoms, the remainder representing H; (iii) compounds represented by formula (I) , where each Bl, B2 and B3, independently, represent an acyl group having 6 to 22 carbon atoms; (iv) compounds represented by formula (I) , where each of Bl, B2 and B3 represent H; the weight ratio of the compounds (i) / (ii) / (iii) being 46-90/9-35/1-15, the weight ratio of component (a) to component (b) being in the range of 4:1 to 1:10.

The present invention also provides a method for improving foam properties of surfactant mixtures, which comprises combining an aqueous composition of the current invention with at least one surfactant.

The present invention also provides the use of aqueous compositions of the current invention as foam-enhancing agent or foam booster for surfactant mixtures.

Detailed description of the invention

The aqueous composition of the present invention comprises an alkyl ether carboxylate derived from alkanols having 6 to 22 carbon atoms; and one or more compounds of the following formula (I) :

Formula I

wherein

R' , m, n, 1, Bl, B2, and B3 have the same meaning as defined above, the weight ratio of component (a) to component (b) being in the range of 4:1 to 1:10.

The alkyl ether carboxylate derived from alkanols having 6 to 22 carbon atoms used as component (a) is one satisfying the following formula (II) :

R-0-(CH₂CH₂0)_n-CH₂COO- M⁺ Formula II wherein R is an alkyl residue having 6 to 22 carbon atoms, n has a value in the range of 2 to 10, preferably 2.5 to 7, and M+ is an appropriate cation, preferably selected from the group consisting of an alkali metal, an alkaline earth metal, ammonium, an alkylammonium, an alkanolammonium or a glucammonium.

Particularly preferred are compounds of the above formula (II) wherein R is an alkyl residue having 12 to 14 carbon atoms, particularly 12 carbon atoms; n has a value in the range of 2.5 to 5 and M⁺ is an alkali metal cation such as sodium or potassium. Alkyl ether carboxylates are preferably used as liquid diluted aqueous solutions having a solid content lower than 30 wt.-%.

Alkyl ether carboxylates are obtained by ethoxylation and subsequent carboxymethylation of fatty alcohols.

The process is divided into two steps. The first one is the ethoxylation of alcohols under standard conditions known by the skilled in the art. However, one may also start from commercially available ethoxylated alcohols.

In the second step, the ethoxylated alcohols are reacted with a strong base, like sodium or potassium hydroxide, in presence of a reducing agent, i.e. sodium borohydride, to obtain the corresponding alkoxylate, which is carboxymethylated with sodium monochloroacetate (SMCA).. According to the invention, it is preferred that the degree of carboxymethylation of the ethoxylated alcohols is relatively high, preferably higher than 80%.

Optionally, the crude alkyl ether . carboxylate acid salt can be purified by first converting the crude products with hydrochloric acid or sulphuric acid into the free acid. Said acid is washed and after that it is converted into the corresponding salt.

Examples of commercially available alkyl ether carboxylate acid salts are marketed under the trade name AKYPO® by Kao Chemicals GmbH.

The ethoxylated glycerides used as component (b) are prepared as it is described in the European patent application EP-A-1045021, preferably by reaction of triglycerides, glycerine and ethylene oxide.

The acyl group (-CO-R) , having 6 to 22 carbon atoms, preferably from 12 to 18 carbon atoms, is preferably derived from natural fat and oil as well as synthetic triglycerides. Preferred fats and oils -include palm oil, coconut oil, sunflower oil, rapeseed oil, castor oil, olive oil, soybean oil; and animal fat such as tallow, bone oil; fish oil, hardened oils and semihardened oils thereof; and mixtures thereof. Particularly preferred are acyl groups derived from coconut oil, palm oil and tallow such as beef tallow.

Particularly preferred are compounds of the formula I wherein the weight ratio (i) + (ii) + (iii) / (iv) is in the range of 85/15 to 40/60, more preferably in the range 80/20 to 45/55.

Among the suitable ethoxylated glycerides according to the invention it could be mentioned one which is commercially available under the trademark LEVENOL® H&B (INCI name: Glycereth-2 cocoate) , marketed by KAO Corporation, S.A.

The weight ratio of component (a) to component (b) is in the range of from 4:1 to 1:10, preferably 3,5:1 to 1:5, more preferably 3:1 to 1:1, most preferably 2,5:1 to 2:1.

Those compositions according to the present invention which are used to enhance the foaming of other surfactant composition (in the following referred to as "foam booster") preferably contain 15 to 30 wt.%, more preferably 22 to 28 wt.%, of components (a), i.e. the ethercarboxylate, and (b) , i.e. the ethoxylated glyceride, as defined above. The amount of component (a) is preferably in the range of 10 to 20 wt.%, more preferably 14 to 17 wt.%. The amount of component (b) is preferably in the range of 5 to 10 wt.%, more preferably 6 to 8 wt.%. The active matter content of the foam booster is also preferably within the range 15 to 32 wt.%, more preferably 22 to 32 wt.%, the active matter of the composition is substantially provided by components (a) and (b) . While the foam booster thus does not include significant amounts of other surfactants, it may include ethoxylated alcohol, sodium chloride and impurities, as a result of the preparation process of the alkyl ether carboxylates. The foam booster of the present invention generally do not contain a peaked (narrow range) short chain alcohols since this would unnecessarily increase the costs.

The foam booster of the present invention may be used to improve the foam properties of surfactant mixtures, particularly those containing anionic surfactants, and the invention thus also provides a method for improving foam properties of surfactant mixtures, which comprise combining an aqueous composition of the current invention with at least one surfactant, preferably an anionic surfactant.

' Typical examples of anionic surfactants are soaps, alkylbenzenesulfonates, alkanesulfonates, olefin sulfonates, alkylether sulfonates, glycerol ether sulfonates, α-methyl ester sulfonates, sulfofatty acids, alkylsulfates, fatty alcohol ether sulfates, glycerol ether sulfates, hydroxy mixed ether sulfates, monoglyceride (ether) sulfates, fatty acid amide (ether) sulfates, mono- and dialkyl sulfosuccinates, mono- and dialkyl sulfosuccinamates, sulfotriglycerides, amide soaps, amide ether carboxylic acids and salts thereof, fatty acid isethionates, fatty acid sarcosinates, fatty acid taurides, N-acylamino acids such as, for example, acyl lactylates, acyl tartrates, acyl glutamates, acyl aspartates, alkyl oligoglucoside sulfates, protein fatty acid condensates (particularly wheat-based vegetable products) and alkyl (ether) phosphates.

One of the preferred anionic surfactant is sodium lauryl ether sulfate, particularly preferred is sodium lauryl ether sulfate having an average degree of ethoxylation of 1 to 3, preferably 1 to 2.5, most preferably 2 to 2.5.

The present invention also provides compositions containing the foam booster in combination with other surfactants, particularly one or more of the above-mentioned anionic surfactants (in- the following referred to as "foam booster-containing surfactant mixture" ) . The anionic surfactant is desirably contained in the foam booster-containing surfactant mixture of the present invention in an amount of 3 to 20 wt.-%, preferably 6 to 20 wt.-%, with respect to the total weight of the composition.

The amount of alkyl ether carboxylate in the foam booster-containing surfactant mixture of the present invention is preferably in the range of 1 to 10 wt.-%, preferably 1.5 to 8 wt.-%, with respect to the total weight of the composition. The amount of component (b) is preferably 0.5 to 10 wt.-%, more preferably 0.75 to 5 wt.-%.

According to the invention, it is preferred that the total amount of components (a) and (b) is in the range of 0.5 to 20, preferably 1 to 15, most preferred 2 to 10 wt.-% with respect to the total weight of the composition. Anionic surfactants are preferably present in a weight ratio of the mixture of component (a) and (b) to anionic surfactant (component (c) ) is in the range of 10:1 to 1:10, preferably in the range of 5:1 to 1:5.

The foam booster-containing surfactant mixture of the present invention may contain other surfactants such as non- ionic, cationic and amphoteric surfactants. Amphoteric surfactant includes ampholytes and betaines. Specific examples are alkyl amine oxides, alkyl betaines, alkyl sulphobetaines (sultaines), amidoalkyl betaines, alkyl glycinates, alkyl carboxyglycinates, alkyl amphoacetates, alkyl amphopropionates, alkylamphoglycinates, alkyl amidopropyl betaines, alkyl amidopropyl- and hydroxysultaines . Particularly preferred amphoteric surfactants are alkyl amine oxides, alkyl sulphobetaines (sultaines) , alkylamphoglycinates alkyl amphoacetates such as sodium coco monoamphoacetate or sodium coco diamphoacetate, and alkyl amidopropyl betaines such as cocoamido propyl betaine.

Typical examples of cationic surfactants are quaternary ammonium salts (quats) and the quaternized derivatives of polyalkanolamine esters (esterquats) . Examples of commercially available quats are: Quartamin" AB (Behentrimonium Chloride) , Quartamin^® 60W25 (Cetrimonium Chloride) and Quartamin^® ABK (Behentrimonium Chloride and Cetearyl Alcohol), all marketed by KAO Corporation S.A.

Examples of commercially available esterquats are Quartamin® BTC-131 (Behenoyl PG-Trimonium Chloride) , marketed by KAO Chemicals GmbH, and Tetranyl ® CO-40 (Dioleoylethyl Hydroxyethylmonium Methosulf te and Dipropylene Glycol) marketed by KAO Corporation S.A.

Specific examples of non-ionic surfactants are alkoxylated trimethyolol propane, alkoxylated 1,2,3- trihydroxy hexane, alkoxylated pentaetrythritol, alkoxylated sorbitol, alkoxylated glycerol, alkoxylated glycerol fatty acid ester, alkoxylated trimethyolol propane fatty acid ester, alkoxylated 1, 2, 3-trihydroxy hexane fatty acid ester, alkoxylated pentaetrythritol fatty acid ester, alkoxylated sorbitol fatty acid ester, fatty alcohol polyglycol ethers, alkylphenol^' polyglycol ethers, fatty acid polyglycol esters, fatty acid amide polyglycol ethers, fatty amine polyglycol ethers, mixed ethers and mixed formals, optionally partly oxidized alk(en)yl oligoglycosides or glucuronic acid derivatives, fatty acid-N-alkylglucamides, protein hydrolyzates (particularly wheat-based vegetable products) , polyol fatty acid esters, sugar esters, alkyl polyglucosides, sorbitan esters, polysorbates and alkanolamides, including alkoxylated alkanolamides and alkyl ether carboxylic acid alkanolamides .

Particulary preferred foam booster-containing surfactant mixtures are compositions containing, a part from the foam booster itself, sodium lauryl ether sulfate in combination with cocoamido propyl betaine, with sodium coco monoamphoacetate or with sodium coco diamphoacetate or mixtures thereof.

The pH value of the foam booster-containing surfactant mixture of the present invention is preferably within the range of 4 to 8 , more preferably 5 to 7.

The foam booster-containing surfactant mixture of the present invention may not only be used in personal care products such as body shampoos, hair shampoos, shower baths, liquid soaps and other cosmetic rinse-off products, but also in house-hold applications such as dishwashing products and in laundry applications such as hand washing products. The compositions are particularly useful as hair shampoos and body shampoos.

If the foam booster-containing surfactant mixture of the present invention are used in hair shampoos and body shampoos the total amount of wash active matter, that is, the total amounts of surfactants contained in the composition of the present invention is preferably less than 30 wt.-%. That is, if the composition contains surfactants other than components (a) , (b) and (c) , the total amount of these surfactants and components (a), (b) and (c) does desirably not exceed 30 wt.- %. Moreover, in hair shampoos and body shampoos the weight ratio of the mixture of component (a) and (b) to anionic surfactant (component (c) ) is preferably in the range of 1:3 to 1:5.

The following examples are given in order to provide a person skilled in the art with a sufficiently clear and complete explanation of the present invention, but should not be considered as limiting of the essential aspects of its subject, as set out in the preceding portions of this description.

Examples

The foaming power and the foam density of the compositions shown in Table 1 were determined according to the following methods .

Foaming power

0.1 wt.-% active matter surfactant solutions (pH 6-7; 40°C; 15°dH) were prepared and its foam volume was determined according to the "Reverse Stirring Agitation" method³ in the in the presence of 0.5 wt.-% "Spangler sebum"^b.

This method consists in measuring the foam volume after agitation of 100 g of a diluted solution of the test product, placed into a 400 mL graduated cylinder, the cylinder being attached at its middle section to the axle of a motor and is rotated at 1100 r.p.m. with a metallic stirrer on a vertical plane perpendicular to this axle, changing the direction every 6 seconds during 5 minutes.

The measures were taken 5 times after 30 seconds and after 5 minutes. The lowest and the highest value were neglected. The values shown in table 2 are the average of the 3 remaining results for the mixtures according to the invention (1-4) and also for the comparative experiments (Cl- C10) .

^a(Castan, P.; Winkel, S.; Amela, C; Garcia, A. ; Siscart, N.; Kao Corporation SA, Spain.; "A brief study about foams. Foaming properties of amphoteric surfactants and the correlation between the determination methods applied" Comunicaciones presentadas a las Jornadas del Comi te Espanol de la Detergencia . (1997), 27, 241-255) ^b [ J. Soc . Cosmet . Chem . 32, 271-286, (July-August 1989)] (20 wt.-% olive oil + 15 wt.-% oleic acid + 15 wt.-% Coconut acid + 15 wt.-% Myristyl Myristate + 10 wt.-% palmitic acid + 10 wt.-% paraffin waxes + 5 wt.-% stearic acid + 5 wt.-% Squalane + 5 wt.-% Cholesterol)

Foam density

1 wt.-% active matter surfactant solutions (pH 6-7; 25°C; 15°dH) were prepared and its foam density was determined according to the Bubbling method (X. Domingo, L. Fiquet, H. Meijer "Foam Ability/Stability of Surfactants" Tenside Surf. Det . 29 (1992) l,pp. 16-22) . This parameter can be correlated to the ability of surfactant solutions to form close, dense lathers.

The foam density is measured after 30 seconds in duplicate. The values shown in Table 1 are the average of the obtained results. The weight ratio of the different surfactant mixtures are indicated here below:

Table 1 - Foam measurements

¹Sodium laureth-2 sulfate

²SLES/surfactant or mixture of surfactants (3:1 wt.-%)

³Mixture alkyl ether carboxylate/ethoxylated glycerides (2:1 wt. -%)

These examples show that a composition of the present invention (Ex. 1) shows a significantly improved foaming behaviour in comparison to the compositions of comparative examples (Cl to C4) which merely differ from the compositions of the present invention with respect to the ethoxylation degree of the two components .

Claims

CLAIMS 1. An aqueous composition comprising

(a) an alkyl ether carboxylate of the following formula II:

Formula II:

R-0-(CH₂CH₂0)_n-CH₂COO- M⁺ wherein

R is an alkyl residue having 6 to 22 carbon atoms; n has a value in the range of 2 to 10, preferably 2.5 to 7; and M⁺ is an appropriate cation selected from the group consisting of an alkali metal, an alkaline earth metal, ammonium, an alkylammonium, an alkanolammonium and a glucammonium;

and

(b) a mixture of compounds of the following formula (I) :

Formula I :

R'

CH₂-0-(CH₂CHO)_m-B₁

R' I CH-0-(CH₂CHO)_n-B₂

R' I CH₂-0-(CH₂CHO)_rB₃ wherein

R' represents H or CH₃; each m, n, and 1 independently represent a number from 0 to 4, the sum of m, n and 1 being in the range of 1 to 4 , and said mixtures of ethoxylated glycerides comprising

(i) compounds represented by formula (I) , where one of Bl, B2 and B3 represents an acyl group having 6 to 22 carbon atoms, the remainder representing H; (ii) compounds represented by formula (I), where two of Bl, B2 and B3, independently, represent an acyl group having 6 to 22 carbon atoms, the remainder representing H; (iii) compounds represented by formula (I), where each Bl, B2 and B3, independently, represent an acyl group having 6 to 22 carbon atoms; (iv) compounds represented by formula (I), where each of Bl, B2 and B3 represent H; the weight ratio of the compounds (i) / (ii) / (iii) being 46-90/9-35/1-15, the weight ratio of component (a) to component (b) being in the range of 4:1 to 1:10.

2. A composition according to claim 1, wherein the weight ratio of component (a) to component (b) is in the range of 3:1 to 1:5.

3. A composition according to any of the preceding claims, wherein, in the compound of formula II, R is an alkyl residue having 12 to 14 carbon atoms, n has a value in the range of 2.5 to 5 and M⁺ is sodium or potassium.

4. A composition according to any of the preceding claims, wherein in the compounds of the formula I the weight ratio (i) + (ii) + (iii) / (iv) is in the range of 85/15 to 40/60.

5. A composition according to any of the preceding claims, wherein the compound of formula I corresponds to Glycereth-2 cocoate.

6. A composition according to any of the preceding claims, wherein the total amount of surfactants (active matter) is in the range of 15 to 32 wt.-% with respect to the total weight of the composition and the total amount of components (a) and (b) is in the range of 15 to 30 wt.-% with respect to the total weight of the composition.

7. A composition according to any of claims 1 to 4, additionally containing (c) an anionic surfactant.

8. A composition according to claim 6, wherein the weight ratio of the mixture (a) and (b) to component (c) is in the range of 10:1 to 1:10, more preferably 5:1 to 1:5.

9. A composition according to claims 6 or 7 , wherein the anionic surfactant is sodium lauryl ether sulfate having an average degree of ethoxylation in the range of 1 to 3.

10. A composition according to any of claims 6 to 8, additionally containing non-ionic, cationic and/or amphoteric surfactants .

11. A composition according to any of claims 6 to 9, having a pH value in the range of 4 to 8.

12. A composition according to any of claims 6 to 10, wherein the total amount of components (a) and (b) is in the range of 0.5 to 20, preferably 1 to 15, most preferably 2 to 10 wt.-% with respect to the total weight of the composition.

13. The use of an aqueous composition as defined in any of claims 1 to 5 as foam-enhancing agent or foam booster for surfactant mixtures.

14. The use according to claim 12, wherein said surfactant mixtures contain anionic surfactants.

15. Method for improving foam properties of surfactant mixtures, which comprise combining an aqueous composition as defined in any of claims 1 to 5 with at least one surfactant.

16. Method according to claim 14, characterised in that said surfactant is an anionic surfactant.