GB2031941A - Concentrated aqueous surfactant compositions - Google Patents

Abstract

Mixtures of a cationic surfactant with at least one other cationic and/or amphoteric and/or nonionic surfactant are obtained as concentrated aqueous compositions in the G phase, containing between 10 and 55% by weight of water.

Description

SPECIFICATION Concentrated aqueous surfactant compositions The present invention relates to novel concentrated aqueous surfactant compositions, which comprise mixtures of different surfactants.

Mixtures of surfactants are prepared and sold for a wide variety of industrial and domestic applications.

They are often required in a fluid form, and it is desirable that they should contain as high a proportion of active material as possible, in order to reduce the costs of storage and transport.

Where the mixture has a melting point below, or only slightly above ambient tem perature it is sometimes possible to supply the composition in the form of an anhydrous mixture, our a mixture containing up to about 5% of water, respectively. In the latter case the trace of water appears to act as a melting point depressor.

However, in the case of surfactant mixtures which are solid at temperatures above about 25"C, it has often been impossible to obtain a fluid composition at concentrations above about 30 to 50% by weight of active ingredient, depending on the nature of the mixture. Small amounts of water up to about 10% do not depress the melting point sufficiently, while larger amounts, sufficient to cause a phase change result in the formation of a rigid gel, rather than a fluid solution. It has generally been found that as the total concentration of active ingredient in a dilute solution approaches a critical level, which is usually about 30 /O by weight but may in the case of some mixtures be higher, e.g. up to about 55% by weight, the viscosity of the solution begins to rise, causing difficulty in preparing and handling the solution.At the critical level the solution sets into an immobile gel or phase separation occurs.

It is sometimes possible to increase the concentration of active ingredient by addition of viscosity modifiers or cosolvents, such as alcohols, which act as thinners, both lowering the viscosity of the solution and inhibiting the formation of gels, so that higher concentrations may be attained. Such cosolvents are normally only effective in producing substantial increases in the attainable concentration when they are present in such large amounts that they constitute a fire hazard, adversely affect the properties of the product for many of its desired end uses and/or increase the cost of the product.

It has been reported (see for example "Advances in Colloid Interface Science" 1 (1967) 79-110 pp.82-83) that some surfactant compounds are capable of forming highly viscous, non-pumpable liquid crystal phases. Some of these compounds form a phase of relatively low viscosity compared with the other liquid crystal phases, which is usually referred to as the "G" or "lamellar phase" and which forms only within a specific concentration range. However, in most instances, including the case of virtually all those compounds which are of industrial interest, where the existence of a "G" phase has been reported, it can only be formed at elevated temperatures. Thus, for example, sodium lauryl sulphate has been reported to form a "G" phase, at about 74"C, which is pourable.However, due to the elevated temperature required, this phenomenon has hitherto been regarded as having purely academic interest. It has never been possible to apply it in industry.

Moreover it has never been reported that mixtures of different kinds of surfactant are capable of forming a "G" phase.

Recently, we have discovered that certain surfactants of commercial value including some ammonium alkyl sulphates and some olefin sulphonates form "G" phases at ambient temperature. As a consequence of this discovery we are now able to prepare these surfactants in a fluid form at very much higher concentrations than could previously have been achieved. (See for example our copending British Patent Application No.2038174.) We have now discovered that certain mixtures of surfactants form a fluid lamellar (G) phase within a narrow range of concentrations lying above the concentration at which the immobile phase forms. This often lies above 60% concentration and may extend as high as 80% of active ingredient.

The mixtures tend to form fluid "G" phases at relatively low temperatures compared with the typical minimum temperatures at which aqueous solutions of most individual surfactants which are capable of forming "G" phases can exist in such a phase. Usually the mixtures can be obtained as a fluid "G" phase at ambient temperatures or by slight warming.

By preparing solutions of such mixtures at the particular concentrations corresponding to the formation of the "G" phase we have been able to obtain pumpable mixtures of surfactants at concentrations of the total active compounds which are in some cases more than double the maximum which has hitherto been attainable. This gives rise to substantial savings in the cost of transporting and storing the products. It has also been discovered that the more highly active compositions of our invention have bacteriostatic properties. The compositions are, generally, unexpectedly easy to dilute back to conventional dilutions, and, in many instances, show little or no tendency to form an intermediate gel phase on addition of sufficient water to effect such dilution.

The invention provides an aqueous surfactant composition consisting substantially of at least 10% and not more than 55% by weight of water and an active mixture consisting of at least 5% by weight of a first, cationic surfactant, together with at least 5% by weight of at least one non-ionic surfactant and/or at least one other cationic surfactant nonhomologous with said first surfactant and/or at least one amphoteric surfactant, said mixture in the presence of water exhibiting a"G" phase at a temperature below 23"C, and the concentration of said mixture corresponding to that at which the composition can exist, at least predominantly in the "G" phase.

The "G" phase is a pumpable phase which is formed over a narrow range of concentrations which range usually lies between 45% and 80% by weight of active ingredient and is characterised by a lamellar structure in which the surfactant molecules are associated to form plates of indefinite size separated by planes of water molecules.

Typically when a surfactant mixture having a composition corresponding to the active ingredients according to the invention is prepared in aqueous solutions of increasing concentration, the molecules are first found to associate in spherical clusters (Micelles), which with increasing concentration become rod-like. At higher concentrations the micelles become more crowded causing a rise in the viscosity of the solution and, in the great majority of cases, eventually lengthen to form a regular hexagonal array of cylindrical surfactant micelles in an aqueous medium (the rigid "met" liquid crystal phase).If the concentration of a surfactant in the "M1" phase is progressively increased a phase change occurs to give either a hydrated solid phase, or, in the case of surfactant mixtures of this invention, to convert the M, phase progressively to a fluid "G" phase until a viscosity minimum is reached.

Further increase in the concentration of the "G" phase causes the viscosity to rise until a further phase change occurs. This may lead to the formation of either a hydrated solid or a second immobile liquid crystal phase (the M2 phase) which resembles the Mt phase in structure, but inverted - i.e. with water as the internal phase and the surfactant as the continuous phase.

The foregoing description is somewhat simplified.

The term "hydrated solid phase" has been used broadly to include those systems which comprise suspensions of solid or immobile gel phases in one or more viscous or gel phase to provide a more or less rigid material usually having a granular appearance under a polarising microscope. No one surfactant has been found which will form all of the various liquid crystal phases, however, surprisingly, all the mixtures of the classes of surfactant specified herein we have so far examined form a fluid "G" phase, even in cases where the individual components do not form "G" phases or form them only with difficulty, e.g. at high temperatures.

In general we have found, to a good approximation, that the proportion of an active mixture having n components which is required to form a "G" phase can be determined from the formula: C1 C2 Cn - + t + .... - = 1,where 91 Q2 C1.... Cn are the concentrations of the individual active components andg..... g, are the concentrations at which each component forms a "G" phase of minimum viscosity. This formula enables the concentration of the mixture corresponding to the minimum viscosity "G" phase to be estimated in a majority of cases.Where g is not known, or a component does not form a "G" phase, or the above formula is not applicable, then any "G" phase can be located very rapidly and easily, using standard laboratory equipment by making a test composition having an active concentration of say 75% (or, where appropriate, whatever concentration has been estimated on the basis of the foregoing formula) and placing a sample on a slide on the block of a heated stage microscope. Examination between crossed polarisers will reveal in which phase the sample is present. The various phases each have a characteristic appearance which is easily identified by comparison for example with the photographs of typical liquid crystal phases in the classic paper by Rosevear, JAOCS Vol. 31 P 628 (1954), or in J. Colloid and Interfacial Science, Vol. 30 No. 4 P. 500.

If the mixture is in an M1 phase, water may be allowed to evaporate from the edges of the sample under the cover disk and any phase changes observed. If an M2 phase or hydrated solid is present water may be added around the edge of the cover disks and allowed to diffuse into the composition. If no "G" phase is located in this way samples may be heated progressively on the block and the operation repeated.

Usually the composition is pumpable at concentrations within a range of t l00/c, preferably t 5% e.g.

2.5% of the minimum viscosity concentration. This rangetendsto be broader at more elevated temperatures. Compositions may be obtained, at the limits of the range in which one or more solid or gel phase is suspended in a continuous "G" phase. Such compositions are often useful on account of their appearance and constitute a particular aspect of the invention.

Typically the compositions of the invention contain two, three or four different kinds of surfactant each in a concentration of more than 10% by weight of the composition.

The compostions of our invention may contain minor amounts of non-surfactant organic solvents, such as glycols or fatty alcohols, and of non-colloidal electrolytes such as sodium chloride, or sulphate.

Such inclusions are often present as impurities in the surfactants. However, we prefer not to add appreciable amounts of solvents to the compositions of our invention. We prefer where possible to maintain the proportion of non-surfactant organic solvent below 5% by weight of the active mixture and preferably below 5% by weight of the total composition. Most preferably the proportion is less than 2% by weight of the total composition e.g. less than 1%. The presence of inorganic salts or similar non-colloidal electrolytes does not generally have the same substantial disadvantages as the presence of organic solvents, but it is nevertheless generally undesirable because it tends to raise the viscosity of the fluid "G" phase. We therefore prefer, generally, that the proportion of non-colloidal electrolyte be maintained within the same limits as those stated in relation to organic solvents. However there are certain circumstances in which the presence of some electrolyte may be useful, e.g. when the melting point of the "G" phase is slightly above ambient, and an increase in the electrolyte content may depress the melting point sufficiently to obtain a pumpable "G" phase without heating. In such circumstances it may sometimes be desirable deliberately to add up to about 6% by weight of electrolyte, usually sodium chloride, or sodium sulphate.

The composition of our invention may optionally contain minor amounts, e.g. up to 5% by weight of the active mixture, of surface active material other than those specified hereinbefore but are preferably substantially free from anionic surfactants.

The active mixtures in the compositions of our invention comprise at least one cationic surfactant.

The cationic surfactant may for example be an alkylammonium salt having a total of at least 8, usually 10 to 30 e.g. 12 to 24 aliphatic carbon atoms, especially a tri ortetra-alkylammonium salt. Typically alkylammonium surfactants for use according to our invention have one or at most two relatively long aliphatic chains per molecule (e.g. chains having an average 8 to 20 carbon atoms each, usually 12 to 18 carbon atoms) and two or three relatively short chain alkyl groups having 1 to 4 carbon atoms each, e.g.

methyl or ethyl groups, preferably methyl groups.

Typical examples include dodecyl trimethyl ammonium salts. Benzalkonium salts having one 8 to 20 C alkyl group one or two 1 to 4 C alkyl groups and a benzyl group are also useful.

Another class of cationic surfactants useful according to our invention are N-alkyl pyridinium salts wherein the alkyl group has an average of from 8 to 22 preferably 10 to 20 carbon atoms. Other similarly alkylated heterocyclic salts, such as N-alkyl isoquinolinium salts, may also be used.

Alkylaryl dialkylammonium salts, having an average of from 10 to 30 aliphatic carbon atoms are useful, e.g. those in which the alkylaryl group is an alkyl benzene group having an average of from 8 to 22, preferably 10 to 20 aliphatic carbon atoms and the other two alkyl groups usually have from -1 to 4 carbon atoms e.g. methyl groups.

Other classes of cationic surfactant which are of use in our invention include alkyl imidazoline or quaternised imidazoline salts having at least one alkyl group in the molecule with an average of from 8 to 22 preferably 10 to 20 carbon atoms. Typical examples include alkyl methyl hydroxyethyl imidazolinium salts, alkyl benzyl hydroxyethyl imidazolinium salts, and 2 alkyl- 1 - alkylamidoethyl imidazoline salts. Another class of cationic surfactant for use according to our invention comprises the amido amines such as those formed by reacting a fatty acid having 8 to 22 carbon atoms or an ester, glyceride or similar amide forming derivative thereof, with a di- or poly amine, such as, for example, ethylene diamine or diethylene triamine, in such a proportion as to leave at lease one free amine group. Quarternised amido amines may similarly be employed.

Typically the cationic surfactant may be any water soluble compound having a positively ionised group, usually comprising a nitrogen atom, and either one or two alkyl groups each having an average of from 8 to 22 carbon atoms.

The anionic portion of the cationic surfactant may be any anion which confers water solubility, such as formate, acetate, lactate, tartarate, citrate, hydrochloride, nitrate, sulphate or an alkylsulphate ion having up to 4 carbon atoms such as a methosulphate. It is preferably not a surface active anion such as a higher alkyl sulphate or organic sulphonate.

At least one cationic surfactant is preferably present in a proportion of from 10 to 90% of the weight of the active mixture, most preferably 20 to 80% by weight, e.g. 30 to 60%. The active mixtures in the composition of our invention optionally comprise at least one amphoteric surfactant. The amphoteric surfactant may for example be a betaine, e.g. a betaine of the formula:

wherein each R is an alkyl, cycloalky, alkenyl or alkaryl group and preferably at least one and most preferably not more than one R has an average of from 8 to 20 e.g. 10 to 18 aliphatic carbon atoms and each other R has an average of from 1 to 4 carbon atoms.Particularly preferred are the quaternary imidazoline betaines of the formula:

wherein R and R1 alkyl, alkenyl, cycloalkyl, aikaryl or alkanol groups having an average of from 1 to 20 aliphatic carbon atoms and R preferably has an average of from 8 to 20 e.g. 10 to 18 aliphatic carbon atoms and R' preferably has 1 to 4 carbon atoms. Other amphoteric surfactants for use according to our invention include alkyl amine ether sulphates, sulphobetaines and other quaternary amine or quaternary amine or quaternised imidazoline carboxylic acids and their salts and Zwitterionic surfactants e.g. taurides, sarcosinates, and amino acids, having, in each case hydrocarbon groups capable of conferring surfactant properties (e.g. alkyl, cycloalkyl, alkenyl or alkaryl groups having from 8 to 20 aliphatic carbon atoms).Typical examples include + C12 H24 N (CH3)2 CH2 COO - , di-tallowyl carboxymethyl imidazoline, and N-tallowyl - N' - carboxymethyl - N'- hydroxyethyl ethylene diamine. Generally speaking any water soluble amphoteric or Zwitterionic surfactant compound which comprises a hydrophobic portion including a C820 alkyl or alkenyl group and a hydrophilic portion containing an amine or quaternary ammonium group and a carboxylate, sulphate or sulphonic acid group may be used in our invention.

Additionally the compositions of our invention optionally comprise at least one non-ionic surfactant. The non-ionic surfactant is typically a polyalkoxylated fatty alcohol, fatty acid, alkyl phenol, glyceryl ester, sorbitan ester or alkanolamide, wherein, in each case there is an alkyl group containing an average of from 8 to 22, preferably 10 to 20, carbon atoms and a polyalkylene oxy group, usually containing an average of from 1 to 20, e.g. 3 to 10 alkylene oxy units. The alkyleneoxy units are normally ethylenoxy units, but the group may also contain some propyleneoxy units. The alkyl and alkoxylated alkyl amine oxides having at least one alkyl group with an average of from 8 to 22 carbon atoms are also included among the non-ionic surfactants which are suitable for use in our invention.The nonionic surfactant may be present in a total proportion of up to 95% of the weight active mixture, preferably 10 to 75%, most preferably 15 to 50 /O e.g. 20 to 45%.

It will be understood that the various surfactants referred to herein will each, in practice, normally be mixtures of close homologs so that the figures quoted for the size of the alkyl or polyoxyalkylene groups are in each case averages. Homologs in the present context means molecules differing only in respect of the number of carbon atoms in their respective alkyl groups, andlorthe number of alkyleneoxy or other repeating monomer units in a polyalkyleneoxy or similar polymeric chain.

The compositions of our invention may be prepared by mixing the individual surfactants in the presence of the correct proportion of water to obtain the product in the "G" phase. Where all the active components form a "G" phase it is often convenient to prepare each active component separately in the "G" phase, e.g. by acidifying or quaternising an appropriate precursor amine in the presence of the calculated amount of water, and then mix the components. Where one component only forms a "G" phase at an elevated temperature, that component may be prepared and blended with the other component at appropriately elevated temperatures to ensure that both components are in a pumpable state.Where one component does not form a phase, or forms it only with difficulty and the other component forms a "G" phase more readily it is often convenient to prepare the second component in the "G" phase and, for example, quaternise an amine precursor of the first component in the presence of the second, adding water at a rate sufficient to maintain the whole composition in the "G" phase.

Another method which may be convenient when none of the individual components forms a "G" phase sufficiently readily, is to prepare the mixture by acidifying or quaternising a mixture of amine precursors of the individual surfactants, in the presence of sufficient water to maintain the product in the "G" phase. It is also possible to prepare the active mixture in a form other than the "G" phase and adjust the water content by evaporation from, or diffusion into the mixture. This last method is not, however, usually practicable on an industrial scale.

The invention is illustrated by the following examples wherein all percentages are based on the total weight of the composition: The materials used were identified by the following references (the physical state quoted is that at 23"C).

BAC9O: Aqueous solution of the benzalkonium chloride derivative of a (viscous normal primary C12114 alkyldimethylamine.

liquid) Active matter (mm wt. 348) 89.P/o Free amine 0.5% Benzylchloride 0.05% BT50 Aqueous solution of a normal primary C12i18 alkylamidopropyl (M1 phase) dimethyl carboxymethyl amine betaine.

Active matter (mm wt. 365) 52.3% Free amido amine 2.0% Sodium chloride 7.0 /O BT70 As BT 50 but, (M1 phase) Active matter (mm wt. 365) 70.0 /O Free amido amine 2.7% Sodium chloride 9.4% CDE Diethanolamide of coconut fatty acid at 90% purity with (mobile the remainder being free amine, free ester, and glycerol.

liquid) MAB Aqueous solution of a normal primary C,2/14 alkyltrimethyl (M1 phase) amine methosulphate.

Active matter (mm wt. 347) 77.5% Free methanol 3.0 /O Free amine 0.7% OY70 Aqueous solution of a commercial normal primary C12114 alkyl (M1 phase)three mole ethoxy dimethyl amine oxide.

Active matter (mm wt. 397) 68.P/o Free amine 1.2% BB70 Aqueous solution of a normal primary C,2/,4 alkyl (M1 phase) dimethylcarboxymethyl amine betaine.

Active matter (mm wt. 279) 72.2% Free amine 0.4% Sodium chloride 16.8% TIM Aqueous solution of 1-methyl-2 tallow alkyl-3 tallow (viscous alkylamidoethyl - imidazolinium - methosulphate.

paste) Active matter (mm wt. 760) 65.2% Glycerol 3.5% Free fatty matter 1.0% Example 1 A mixture was prepared by blending together 52 parts of BAC 90,37.5 parts of CDE and 10.5 parts water.

The mixture, having a total surfactant concentration of 81% was a fluid lamellar liquid identified as G phase. On dilution with water to a total surfactant concentration of 77% the mixture formed a gel.

Examples 2 to 8 were prepared in the same man neras Example 1 as follows:

Examples 2 - & Number Mixture (X) Active Concentrations (X) Total active at which M1 phase is formed by dilution with water(%) 2 27.7, BAC90 24.8 47.5, 8T50 24.8 24.8, CDE 22.3 71.9 66 3 30.7, MAB 23.8 45.5, BT50 23.8 23.8, CDE 21.4 69.0 60 4 4 27.9, BAC90 25.0 35.7, BT70 25.0 36.4, OY70 25.0 75.0 72 5 43.8, BAC90 39.3 56.2, BT70 39.3 78.6 68 6 44.6, BAC90 40.0 55.4, BB70 40.0 80.0 78 7 43.4, BAC90 38.9 56.6, 0Y70 38.9 77.8 76 8 8 78.0, TIM 50.9 13.6, BAC90 12.2 8.4, CDE 7.6 70.7 59 In each case the product of the example was a mobile G phase at 20 C.

Example 9 A stirred jacketed flask, equipped with a means of recycling material from the bottom to the top of the flaskto assist mixing was charged with 5009 of a 90% solution of a C12114 alkyl benzyl ammonium chloride. The surfactant solution which was a clear mobile liquid in the L2 phase was heated to 55 C, and 3779 of an amido amine of the formula CH3 RCONHCH2CH2CH2N (R = 75% coconut + 25% tallow, MMW = 305) CH3 was charged over 45 mins., together with sufficient quantity of a solution of 122.79 chloracetic acid in 909 water to maintain the pH in the range 7-8. The remaining chloracetic acid was then added, and the pH was raised to 8 by the addition of 47% sodium hydroxide solution.The temperature was raised to 65 C, and the pH was maintained in the range 8-8.5 fora further 10 hrs., when it was no longer necessary to add sodium hydroxide to maintain a constant pH indicating that quaternisation was substantially complete. Approximately 1 10.6g of 47% hydroxide solution was required.

In this example an amido amine betaine was prepared in the presence of a cationic surfactant and the blend had a total surfactant concentration of 75% in a weight ratio of 1:1 amphoteric:cationic surfactant.

During the addition of the amido amine and chloracetic acid solution the material formed a G phase, and remained in this phasethroughoutthe reaction.

Example tO Stirred, jacketed flask equipped with a means of recycling material from the bottom to the top of the flask to assist mixing was charged with 1 56g of a 90% solution of a C12/14 alkyl benzyl ammonium chloride, 156g of 90% pure coconut diethanolamide and 151g of an 88% pure amine derived from C12114 ethoxylated alcohol having the formula CH3 R - (OCH2CH2)n N , where the average value of n = 3 CH3 together with 81.59 water and 1.29 EDTA. The mixture ofsurfactants and precursor was heated to 60"C and 569 of 27% solution of H202 was added over a 1 hour period. The reaction temperature was raised to 65"C. After 12 hours reaction the product was analysed and found to contain 2.4% unreacted amine indicating a conversion of amine to amine oxide 90%.

In this example an amine oxide was prepared in the pressure of a cationic and a non-ionic surfactant to give a total surfactant concentration of 67% in a 1~1~1 ratio of nonionic:cationic:nonionic surfactants.

The product was a mobile G phase throughout the reaction.

Claims (13)

1. An aqueous surfactant composition consisting substantially of at least 100/o and not more than 55% by weight of water and an active mixture consisting of at least 5% by weight of a first cationic surfactant, together with at least 5% of at least 1 nonionic surfactant and/or at least one other cationic surfactant non-homologous with said first surfactant and/or at least 1 amphoteric surfactant, said mixture in the presence of water exhibiting a "G" phase atatemp- erature below 230"C and the concentration of said mixture corresponding to that at which the composition can exist, at least predominantly in the "G" phase.

2. Acomposition according to claim 1,wherein the active components are each capable of forming a "G" phase with water at concentrations respectively of g g and are present in the compositions respectively at concentrations of c, . . cn such that C1 + C2 + On = 1 g1 Q2 Qn

3. A composition according to either of claims 1 and 2, wherein the graph of viscosity against the concentration of active mixture in water exhibits a minimum value corresponding to the formation of the "G" phase and wherein the proportion of active mixture present in the composition lies within + 10% of the concentration corresponding to the mini mum value.

4. A composition according to claim 3, wherein the concentration of the active mixture lies within t 5% of the concentration corresponding to the minimum.

5. A composition according to claim 4, wherein the concentration of the active mixture lies within + 2.5% of the concentration corresponding to the minimum.

6. A composition according to any foregoing claim, wherein at least two different active components are each present in proportions of more than 10% by weight of the composition.

7. A composition according to any foregoing claim containing less than 5% by weight of non-surfactant organic material based on the weight of the active mixture.

8. A composition according to claim 7 containing less than 2% of non-surfactant organic material based on the weight of the total composition.

9. A composition according to claim 8 substantially free from non-surfactant organic solvent.

10. A composition according to any foregoing claim containing less than 5% of non-colloidal electrolyte based on the weight of the active mixture.

11. A composition according to claim 10 containing less than 2% by weight of non-colloidal electrolyte based on the weight of the total composition.

12. Acomposition according to anyforegoing claim substantially as described herein with reference to the examples.

13. A method for preparing of a composition according to any foregoing claim, which comprises mixing together the surfactants in the presence of the appropriate quantity of water.