EP2655590A2 - Cleaning composition and method - Google Patents

Abstract

A cleaning composition comprises a water-in-oil emulsion, having a plurality of independent aqueous phases. An aqueous phase comprises a bleaching agent.

Description

CLEANING COMPOSITION AND METHOD

This invention relates to cleaning compositions and cleaning methods, employing water-in-oil emulsions.

Consumers are aware that in order to achieve effective cleaning of household items and surfaces often bleaches (e.g. sodium hypochlorite bleaches) have to be employed. The bleaches are able to act upon stains and can cause the chemical disruption (oxidation) of the stain and / or its decolouration, and thus masking of the stain. Bleaches also provide an anti-microbial action. Bleach performance is dependent upon several factors including the type and concentration of the bleach used. One crucial factor is that of temperature. Many bleach / bleach pre-cursors only reach the required level of activity at or above a certain elevated temperature.

In order to reduce this temperature and thus make the bleaches more convenient to use whilst saving unnecessary energy bleach activators are employed. These bleach activators interact with the bleach / bleach pre-cursor, forming new bleaching species, which are more active at lower temperature.

One major issue with the use of bleach activators with bleaches is that due to the reactivity of the two compounds they must be kept separate until the desired point of use. This is relatively facile when the bleach and bleach activator is in solid form since the reaction between the two is prevented. Thus cleaning powders and compressed particulate tablets can be produced which contain both bleach and bleach activator in solid form. Additionally often the bleach and bleach activators are segregated with the composition as a further aid to prevent premature reaction .

However, certain cleaning preparations require the use of a liquid bleaching formulation. In such a case the facile separation solution cannot easily be achieved since the bleach and bleach activator are free to migrate within the liquid and will, if they come into contact, react with one another. Thus traditionally it has been necessary to provide liquid cleaning formulations in multi-chamber packs, wherein one chamber contains bleach and one chamber contains a bleach activator, so that the bleach and bleach activator are only brought into contact at the point of use. Such twin chamber packs are expensive to manufacture and cumbersome in use, requiring an unnecessary burden of dexterity from a consumer.

It is an object of the present invention to obviate / mitigate the disadvantages described above. According to a first aspect of the present invention there is provided a cleaning composition comprising a water-in-oil emulsion, having a plurality of independent aqueous phases, wherein an aqueous phase comprises a bleaching agent. With the use of a composition in accordance with the present invention it has been found that a liquid formulation may be provided which displays excellent stability before use and outstanding bleaching performance in use due to the combination of bleach and bleach activator. Additionally the exceptional performance is imparted without the need for a complex multi-chamber sales pack.

Additionally it has been found that the cleaning composition may be rapidly dispersed, e.g. into a wash liquor. This is increasingly important as wash cycles are becoming shorter / using less water for ecological reasons.

Preferably the composition comprises two independent aqueous phases .

Generally the composition comprises a bleach activator. The bleach activator may be present in an aqueous phase or in an oil phase. Generally the bleach activator is segregated from the bleaching agent. Preferably the bleaching agent is segregated from other detersive agents that react detrimentally with bleaching agents, e.g. enzymes, dyes, fragrances. The bleach activator is possibly in particulate form.

Where the bleach activator is in particulate form generally it has a particle size of 0.0001 to 2mm, e.g. such as 1mm.

Preferably the bleach activator is selected from tetraacetylethylendiamine (TAED) , acetylated triazine derivatives, in particular 1, 5-Diacetyl-2 , 4-dioxohexahydro- 1, 3, 5-triazine ( DADHT ) , acetylated glycoluriles , in particular Tetraacetylglycolurile (TAGU) , acylimides, in particular n-nonanoylsuccinimide (NOSI) , acetylated phenolsulfonates , in particular n-nonanoyloxi or n- lauroyloxibenzolsulfonate (NOBS and/or PRAISE) , acetylated phenol carbonic acids, in particular nonanoyloxi or decanoyloxibenzoesaeure (NOBA and/or DOBA) , carbonic acid anhydrides, acetylated sugar derivatives, in particular pentaacetylglucose (PAG) , pentaacetylfructose, tetraacetylxylose and octaacetyllactose as well as acetylated N-alkylated glucamine and gluconolactone, and/or N- acetylated lactams, for example N-Benzoylcaprolactam. Hydrophilically substituted ecyl acetals and ecyl lactams are likewise preferentially used. Particularly preferential bleach activators are TAED and DOBA.

Bleaching catalysts may be present. Preferred examples include complexes of manganese, iron, cobalt, ruthenium, molybdenum, titanium or vanadium.

When using metal salts in particular manganese salts are in the oxidation state +2 or +3 preferentially, for example manganese halides, whereby the chloride is preferential. Manganese sulfate, manganese salts of organic acids such as manganese acetates, acetylacetonate, oxalates as well as manganese nitrates are suitable.

Metal complex with macromolecular ligands may be used such asl, 4, 7-Trimethyl-l, 4, 7-triazacyclononane (me-TACN) , 1,4,7- Triazacyclononane (TACN) , 1, 5, 9-Trimethyl-l , 5, 9- triazacyclododecane (me-TACD) , 2-Methyl-l , , 7 trimethyl- 1, 4, 7-triazacyclononane (MeMeTACN) and/or 2-Methyl-l , 4 , 7 triazacyclononane (Me/TACN) or ligands such as 1,2-bis (4,7- Dimethyl 1 , 4 , 7-triazacyclonono-i-yl ) ethane (Me4-DTNE) . The bleaching agent is usually a source of active oxygen, e.g. urea / hydrogen peroxide. The bleaching agent may be based on alternative chemistry, e.g. chlorine based bleaching agents, such as hypochlorite bleaches.

Some bleaching agents, such as phthalimido-peroxy-hexanoic- acid (PAP) per-salts such as; perborate, percarbonate, persulphate; are substantially insoluble in water (e.g. having a solubility of less than 0.6g/litre of demineralised water at 25°C. In this case it is preferred that the bleaching agent is suspended in an aqueous phase or in an oil phase. Thus according to one preferred embodiment there is provided a cleaning composition comprising a water-in-oil emulsion, having a plurality of independent aqueous phases, wherein a substantially water insoluble bleaching agent is suspended in an aqueous phase or an oil phase.

Where the bleaching agent is in particulate form generally it has a particle size of 0.0001 to 2mm, e.g. such as 1mm.

The concentration of the hydrogen peroxide is typically from 0.1 to 50%, e.g. 15%.

Preferably the aqueous phases comprises at least 40% by weight of the composition, preferably at least 50% by weight, more preferably at least 60%, more preferably at least 70% and most preferably at least 75% by weight of the composition . The oil phase preferably comprises at least 1%, more preferably at least 3%, more preferably at least 5%, and most preferably at least 7% by weight of the composition. The oil phase preferably comprises less than 45%, more preferably 35%, and most preferably less than 30% by weight of the composition. Preferably the oil phase comprises about 25% by weight of the composition.

The oil phase may be based on widely diverse groups of oils, including natural oils, and mixtures thereof. In this regard reference is made to co-pending European patent application published as EP-A-1749880 which describes oils suitable for forming the oil phase of the emulsion. Generally the oil phase comprises a mineral oil / hydrocarbon such as a paraffin / kerosene.

A common problem with the use of emulsions is that there is often some transport between the oil and water phases. Preferred compositions of the invention have substantially no transport between the oil and water phases. To avoid problems associated with transport between phases, the composition of the present invention preferably further comprises up to 10% by weight of a surfactant, preferably up to 8%, more preferably up to 5%, preferably up to 3%, and most preferably up to 2% by weight of the total composition. It is postulated that the surfactant forms a micelle type barrier around the water particles present in the emulsion.

Preferably the composition comprises at least 0.01% by weight surfactant, preferably at least 0.05%, more preferably at least 0.1% and most preferably at least 0.2% by weight.

The cleaning composition desirably includes at least one surfactant selected from anionic, cationic, non-ionic or amphoteric ( zwitterionic) surfactants. In this regard reference is made to co-pending European patent application published as EP-A-1749880 which describes surfactants suitable for use in the emulsion.

Especially preferred surfactants are those formed by the reaction of succinic acid I or succinic anhydride II, with a polyol, a polyamine or a hydroxylamine .

I Π

R is a hydrocarbon group having from about 12 to about 200 carbon atoms, preferably 12 to about 100 carbon atoms, more preferably 12 to 50 and most preferably 18 to 30 carbon atoms.

The hydrocarbon group R in the above formulae may be derived from an alpha-olefin or an alpha-olefin fraction. The alpha-olefins include 1-dodecene, 1-tridecene, 1- tetradecene, 1-pentadecene , 1-hexadecene, 1-heptadecene , 1- octadecene, 1-eicosene, 1-tricontene, and the like. The alpha olefin factions that are useful include Ci₅-i_a alpha- olefins, Ci₂-i6 alpha-olefins, C₁₄-ie alpha-olefins , Ci₄-ie alpha-olef ins , Ci6-i8 alpha-olefins, C₁₈-24 alpha-olefins , C18-30 alpha-olefins , and the like. Mixtures of two or more of any of the foregoing alpha-olefins or alpha-olefin fractions may be used.

In one embodiment, R in the above formulae is a hydrocarbon group derived from an olefin oligomer or polymer. The olefin oligomer or polymer may be derived from an olefin monomer of 2 to about 10 carbon atoms, and in one embodiment about 3 to about 6 carbon atoms, and in one embodiment about 4 carbon atoms. Examples of the monomers include ethylene; propylene; 1-butane; 2-butane; isobutene; 1-pentene; 1- heptene; 1-octane; 1-nonene; 1-decene; 2-pentene; or a mixture of two or more thereof.

In a preferred embodiment, R in the above formulae is a polyisobutene group. The polyisobutene group may be made by the polymerization of a C₄ refinery stream having a butene content of about 35 to about 75% by weight and an isobutene content of about 30 to about 60% by weight. In one embodiment, R in the above formulae is a polyisobutene group derived from a polyisobutene having a high methylvinylidene isomer content, that is, at least about 50% and in one embodiment at least about 70% methylvinylidenes . Suitable high methylvinylidenes polyisobutenes include those prepared using boron trifluoride catalysts. The preparation of such polyisobutene in which the methylvinylidene isomer comprises a high percentage of the total olefin composition is described in US Patents 4,152,499 and 4,605,808, the disclosure of each of which are incorporated herein by reference . To form the surfactant used in the present invention, those succinic acids or anhydrides are reacted with polyols, polyamines or hydroxyamines . Suitable polyols include: ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, dibutylene glycol, tributylene glycol, 1-2-butanedoil, 2 , 3-dimethyl- 2, 3-butanediol, 2 , 3-butanediol , 2 , 3-hexanediol , 1,2- cyclohexanediol, pentaerythritol, dipentaerythritol, 1,7- heptanediol, 2 , 4-heptanediol , 1, 2 , 3-hexanetriol, 1,2,5- hexantriol, 2, 3, 4-hexantriol, 1, 2, 3-butanetriol, 1,2,4- butanetriol, 2,2,6, 6-tetrakis- (hydroxymethyl) cyclohexanol, 1, 10-decanediol , digitalose, 2-hydroxymethyl-2-methyl-l , 3- propanediol- (tri-methylolethane) , or 2-hydroxymethyl-2- ethyl-1, 3-propanediol- (trimethylolpropane) , and the like, or mixtures thereof; sugars, starches, or mixtures thereof, for example erythritol, threitol, adonitol, xylitol, sorbitol, mannitol, erythrose, fucose, ribose, xylulose, arabinose, xylose, glycose, fructose, sorbose, mannose, sorbitan, glucosamine, sucrose, rhamnose, glyceraldehydes, galactose, and the like; glycerol, diglycerol, triglycerol, and the like, or mixtures or isomers thereof; monooleate of glycerol, monostearate of glycerol, monooleate of sorbitol, distearate of sorbitol, di-dodecanoate of erythritol, or mixtures thereof.

Suitable polyamines may be aliphatic, cycloaliphatic, heterocyclic or aromatic. Examples include alkylene polyamines and heterocyclic polyamines. Suitable alkylene polyamines include ethylene polyamines, butylene polyamines, propylene polyamines, pentylene polyamines, etc. The higher homologues are related to heterocyclic amines such as piperazines and N-amino alkyl- substituted piperazines are also included. Specific examples of such polyamines include ethylene diamine, triethylene tetramine, tris- ( 2-aminoethyl ) amine, propylene diamine, trimethylene diamine, tripropylene tetramine, tetraethylene pentamine, hexaethylene heptamine, pentaethylene hexamine or a mixture of two or more thereof.

The polyamine may also be selected from the heterocyclic polyamines, for example aziridines, azetidines, azolidines, tetra- and dihydropyridines , pyrroles, indoles, piperidines, imidazoles, di- and tetra-hydroimidazoles, piperazines, isoindoles, purines, morpholines, thiomorphines , N- aminoalkylmorpholines , N-aminoalkylthiomorpholines, N- aminoalkylpiperazines , Ν,Ν' -diaminoalkylpiperazines , azepines, azocines, azecines and tetra-, di- and perhydro derivatives of each of the above and mixtures thereof. Useful heterocyclic amines are the saturated 5- and 6- membered heterocyclic amines containing only nitrogen, oxygen and/or sulfur in the hetero ring, especially the piperidines, piperazines, thiomorpholines , morpholines, and pyrrolidines. Suitable compounds include piperidine, aminoalkyl-substituted piperidines, piperazine, aminoalkyl- substituted piperazines, morpholine, aminoalkyl-substituted morpholines, pyrrolidine, and N-aminoalkyl-substituted pyrrolidines such as N-aminopropylmopholine, N- aminoethylpiperazine, and N, N' -diaminoethylpiperazine . Suitable hydroxyamines may be a primary, secondary or tertiary amine. The hydroxyamine may be an N- (hydroxyl ) - substituted alkyl amine, a hydroxyl-substituted polyalkoxy analogue thereof, or a mixture of such compounds . The hydroxylamine suitably contains from about 1 to about 40 carbon atoms, preferably 1 to 20 carbon atoms, more preferably 1 to 10 carbon atoms.

Primary, secondary and tertiary hydroxyamines may represented by the following formulae:

H,N R'— OH

wherein each R is independently an alkyl group of one to about eight carbon atoms or hydroxyl-substituted alkyl group of about two to about 18 carbon atoms. Typically each R is a lower alkyl group of up to seven carbon atoms. The group -R' -OH in such formulae represents the hydroxyl-substituted hydrocarbon group. R' can be an acrylic, alicyclic or aromatic group. Typically, R' is an acyclic straight or branched alkylene group such as an ethylene, 1 , 2-propylene, 1, 2-butylene, 1 , 2-octadecylene , etc, group. When two R groups are present in the same molecule they can be joined by a direct carbon-to-carbon bond or through a heteroatom (e.g., oxygen, nitrogen or sulfur) to form a 5-, 6-, -7 or 8- members ring structure. Examples of such heterocyclic amines include N- (hydroxyl lower alkyl)- morpholines, thiomorpholines , piperidines, oxazolidines, thiazolidines and the like.

The hydroxyamines may be either N- (hydroxy-substituted hydrocarbyl ) amines . These may be hydroxyl-substituted poly) alkoxy) analogues of the above-described hydroxy amines (these analogues also include hydroxyl-substituted oxyalkylene analogues). Such N- (hydroxyl-substituted hydrocarbon) amines may be conveniently prepared by reaction of epoxides with afore-described amines.

Polyamine analogues of these hydroxy amines, especially alkoxylated alkylene polyamines (e.g. N, - (diethanol ) - ethylene diamine) may also be used.

Specific examples of alkoxylated alkylene polyamines include N- (2-hydroxyethyl) ethylene diamine, N,N-bis(2- hydroxyethyl ) -ethylene-diamine, 1- (2-hydroxyethyl) piperazine, mono (hydroxypropyl) -substituted diethylene triamine, di (hydroxypropyl ) -substituted tetraethylene pentamine, N- ( 3-hydroxybutyl ) tetramethylene diamine, etc. Higher homologues are also useful.

Examples of the N- (hydroxyl-substituted hydrocarbyl) amines include mono-, di-, and triethanolamine, diethylethanolamine, di ( 3-hydroxylpropyl ) amine, N-(3- hydroxybutyl) amine, N- ( 4-hydroxybutyl ) amine, N-,N-di-(2- hydroxypropyl ) amine, N- ( 2-hydroxylethyl ) morpholine and its thio analogue, N- (2-hydroxyethyl ) cyclohexylamine, N-3- hydroxyl cyclopentyl amine, o-, m- and p-aminophenol , N- (hydroxylethyl) piperazine, N, N' -di (hydroxylethyl ) piperazine, and the like.

Further hydroxyamines are the hydroxy-substituted primary amines described in US Patent 3,576,743 by the general formula

R_a-NH₂ wherein R_a is a monovalent organic group containing at least one alcoholic hydroxy group.

Specific examples of the hydroxy-substituted primary amines include 2-amino-l-butanol, 2-amino-2-methyl-l-propanol , p- (beta-hydroxyethyl) -aniline, 2-amino-l-propanol, 3-amino-l- propanol, 2-amino-2-methyl-l , 3-propanediol, 2-amino-2-ethyl- 1, 3-propanediol , N- (betahydroxypropyl) -N' - (beta-aminoethyl ) - piperazine, tris- (hydroxymethyl ) aminoethane (also known as trismethylolaminomethane) , 2-amino-l-butanol, ethanolamine, beta- (beta-hydroxyethoxy) -ethylamine, glucamine, glucosamine, 4-amino-3-hydroxy-3-methyl-l-butene, N- 3 (aminopropyl) -4- (2-hydroxyethyl) -piperadine, 2-amino-6- methyl-6-heptanol, 5-amino-l-pentanol , N-(beta- hydroxyethyl ) -1 , 3-diamino propane, 1 , 3-diamino-2- hydroxypropane, N- (beta-hydroxyethoxyethyl ) -ethylenediamine, trismethylol aminoethane and the like.

Hydroxyalkyl alkylene polyamines having one or more hydroxyalkyl substituents on the nitrogen atoms, are also useful . Examples include N- (2-hydroxyethyl) ethylene diamine, N, N-bis ( 2-hydroxyethyl ) ethylene diamine, 1-

2 (hydroxyethyl ) -piperazine, monohydroxypropyl- substituted diethylene triamine , dihydroxypropyl-substituted tetraethylene pentamine, N- ( 3-hydroxybutyl ) tetramethylene diamine, etc. Higher homologues are also useful.

Other preferred surfactants include span 85 (sorbital trioleate) which has an HLB value of 1.8, octylphenol-l- ethyleneancy which has an HLB value of 4.0 and span 80 sorbital monocleate which has an HLB value of 4.3.

Other known surfactants not particularly described above may also be used. Those having an HLB value of less than 10 are preferred. Such surfactants are described in McCutcheon' s Detergents and Emulsifiers, North American Edition, 1982; Kirk-Othmer, Encyclopaedia of Chemical Technology, 3rd Ed., Vol. 22, pp 346-387. The particles of TAED may be coated / may have been brought into contact with a surfactant to aid the dispersion of the TAED particles in the oil phase.

Preferred dispersants are certain nonionic surfactants which act by steric hindrance and are active only at the protectant solid/organic liquid interface and do not act as emulsifying agents. Such dispersants are suitably made up of:- (a) a polymeric chain having a strong affinity for the liquid, and

(b) a group which will absorb strongly to the solid. Examples of such dispersants are those of the Hypermer and Atlox lines, available from the ICI group of companies, including Hypermer PS1, Hypermer PS2, Hypermer PS3, Atlox LP1, Atlox LP2 , Atlox LP4, Atlox LP5, Atlox LP6, and Atlox 4912 and Agrimer polymers such as Agrimer AL-216 and AL-220, available from GAF.

The oil and or water phase of the composition may contain other detergent actives such as enzymes, builders, perfumes, optical brighteners, soil suspending agents, dye transfer inhibition agents.

According to the second aspect of the invention there is provided a method of preparation of a composition comprising a water-in-oil emulsion, having a plurality of independent aqueous phases, comprising the formation of a plurality of independent water-in-oil emulsions and mixing same together under low shear conditions.

According to the third aspect of the invention there is provided use of a cleaning composition prepared according to the second aspect of the invention in a cleaning operation.

According to the fourth aspect of the invention there is provided use of a cleaning composition comprising a water- in-oil emulsion, having a plurality of independent aqueous phases, wherein an aqueous phase comprises a bleaching agent in a cleaning operation. It will be understood that features of the first aspect of the invention will be taken to apply mutatis mutandis to the second aspect of the invention. It has been found that in use the emulsion may break down under shear stress or dilution allowing the bleach activator to interact with the bleach. It has also been found that the emulsion can break down when evaporation of at least a portion of the emulsion is allowed / induced, allowing the bleach activator to interact with the bleach. Further it has been found that the emulsion can break down when placed in contact with a de-stabilising surface.

The use is preferably for cleaning hard surfaces e.g. in a dishwashing or kitchen / bathroom / toilet / sanitary ware cleaning operation. Alternatively the use may be associated with a washing machine and be for mechanical laundry and / or dishwashing. The use may also be for hand washing e.g. manual laundry.

The invention is further illustrated with reference to the following non-limiting Examples.

Materials .

Water was purified by passing through an Elgastat Prima reverse osmosis unit followed by a Millipore Milli-Q reagent water system. Its surface tension was 71.9 mN irf¹ at 25°C, in good agreement with literature. The oils n-dodecane (Sigma Aldrich, > 99%), squalane (Sigma Aldrich, 99%), 0.65 cSt polydimethylsiloxane (PDMS, Dow Corning 200 Fluid, Sigma Aldrich) and rapeseed oil (Tesco) were columned either twice or four times over neutral aluminium oxide 90 (Merck) to remove polar impurities. The surfactant Emulsogen OG consists of oleyl hydrophobic chains bonded to polyglcerol and has an average molecular structure of 2 oleyl chains bonded to 2 glycerol units and so is denoted here with the abbreviation 0₂G₂. The average structure was determined from the manufacturer' s (Clariant) information on the average number of glycerol units per molecule and the measured saponification number to derive the number of oleyl chains. Anfomul 2887, an alkanolamine derivative of polyisobutene lactone, is a surfactant which is commonly used to stabilise emulsion explosive HIPEs¹⁶ and was supplied by Croda. Sodium bis-2-ethylhexylsulphosiccinate (AOT, Aldrich, 98%) was used as received. The transferring species sodium hypochlorite (BDH, 12 w/v available chlorine), hydrochloric acid (Fisher Chemicals, 36 % solution), hydrogen peroxide (FMC corporation, 50 wt% solution) and indicator species potassium permanganate (Sigma Aldrich, >99%), Congo red (Acros Chemicals, 85%) and methyl orange (Sigma Aldrich, 85%) were used as received. Prior to use, all hydrogen peroxide solutions were titrated using cerium sulphate with ferroin indicator to determine their accurate concentrations . Additional reagents including urea (Fisher Chemicals, >99%) , acetic acid (Fisher, >99%) , potassium iodide (Sigma, >99%), sodium thiosulphate (Sigma, 99.99%), starch indicator (Sigma), ferroin (Sigma, 0.1 wt% solution), cerium sulphate (Reidel de Haen, >98%), sulphuric acid (Fisher, 98%) and chloroform (Fisher, >99%) were all used as received.

Methods. 10 mL of each high internal phase emulsion was prepared by adding the required volumes of aqueous phase, stabiliser, then oil phase to a 25 x 75 mm (diameter x height) glass tube. The samples were emulsified by either vigorous handshaking for 30 seconds or by using a simple overhead paddle stirrer with a single plastic-coated metal stirrer blade of 20 x 30 mm operating at approximately 100 RPM for 1 minute . Mean drop diameters were measured by optical microscopy. A small volume of the emulsion was extracted from the middle of the emulsion by pipette and diluted into a large volume of the oil used as the continuous phase. Diluted samples were held in a 25 x 75 mm cavity microscope slides with a single cavity of 16 mm diameter and 0.2 mm depth which was covered with a cover slip. Micrographs of this diluted emulsion were obtained using a Leica DME transmission microscope equipped with a Leica DFC 290 camera. The entire sample field was scanned before acquisition of a micrograph to ensure the final image was representative of the total emulsion drop size distribution which was determined by measuring the diameters of all the drops appearing in a single micrograph (typically 50 to 100 drops) using Leica LAS image analysis software. All parent emulsion drop size distributions were monomodal with polydispersit ies (equal to the standard deviation divided by the mean) of approximately 50%. The final quoted mean drop radii refer to the number average. For the different systems, mean drop radii were measured for the "parent" HIPEs containing either the transferring or indicator species and the mixed HIPE containing both species immediately after preparation. The evolution of the drop size in the mixed HIPE over time was also measured.

To study trapping times, equal volumes of the two "parent" HIPEs containing the transferring and indicator species were mixed by pouring all of one emulsion into another then gently stirring with a spatula four or five times. The vessels were sealed and the mixed emulsions were incubated at 25°C until the colour change indicating transfer had gone to completion. A HIPE in which the two aqueous phases had been premixed was prepared for each system to serve as the reference to show the indicator colour change. The sample and reference emulsions were compared visually to determine the time for the colour change to go to completion. Trapping times were measured at room temperature of 20+3°C.

Values of the partition coefficient of hydrogen peroxide between water and dodecane under different conditions were determined using one of two methods. In the first, low sensitivity method, equal volumes of aqueous hydrogen peroxide and dodecane were equilibrated with gentle stirring for 48 hours. 1 mL of the equilibrated dodecane phase was mixed with 5 mL of 50:50 glacial acetic acid/chloroform and 10 mL of aqueous KI solution (excess) . The iodine liberated was titrated with aqueous sodium thiosulphate solution with starch as indicator²⁶. For the initial peroxide concentrations used here, partition coefficients greater than 5 x 10^"4 could be determined by this method. In the second, high sensitivity method, 1 mL of aqueous hydrogen peroxide solution was equilibrated with 99 mL of dodecane with gentle stirring for 9 days. 90 mL of the equilibrated dodecane phase was then equilibrated with 1 mL of water for 14 days. 0.25 mL samples of this equilibrated aqueous phase was titrated with aqueous cerium sulphate using ferroin as indicator²⁶. Using this method, values of partition coefficient lower than 10^"7 could be measured (dependent on the initial peroxide concentration) . Samples containing no peroxide were also measured as controls.

Results and Discussion Theoretical considerations .

A typical experiment to determine the time over which aqueous reagents are maintained in separate water drop compartments of a HIPE was performed as follows. A first HIPE (HIPE1) is prepared containing a concentration c_Ai of an aqueous reagent A, volume fraction of oil φ_0ΐ with mean water drops radius rj.. The concentration c_Ai is expressed as moles of A per unit volume of water, not the overall emulsion volume. A second HIPE (HIPE2) containing c_B2 of a different aqueous reagent B and volume fraction of oil φ_ο2 with mean water drops radius r₂. Equal volumes of HIPE1 and HIPE2 are mixed to produce a mixed HIPE with overall oil volume fraction φ_σ, mean drop radius r = (ri + r₂) /2 and comparable numbers (depending on the relative values of the radii ri and r₂) of water drops containing either A (at concentration c¾i) or B (at concentration c_B2) . The oil volume fractions of HIPE1 and HIPE2 were generally kept equal such that φ_σι = φ₀2 ⁼ φ_ο· Various pairs of aqueous reagents A and B were examined with A referring to the main transferring species at high concentration and B referring to an appropriate colorimetric indicator species which was present at low concentration. The mixed emulsions were observed visually to determine the time taken for the indicator species B was observed to undergo a colour change. This measured time (t^*) corresponds to the time taken for sufficient A species to transfer from the A-containing droplets into the B-containing droplets such that the colour change occurs. In principle, mass transport of A → B droplets will be accompanied by mass transport of B -> A droplets which will also cause a colour change. However, separate experiments in which HIPE1 was carefully layered on top of HIPE2 followed by observations of where the colour change developed (i.e. in HIPE1 or in HIPE2) showed that A → B dominates under the experimental conditions used here, i.e. high aqueous concentrations of A and very low concentrations of B. This is expected for diffusional mass transport because the relative initial mass transport fluxes are proportional to the concentration gradients which, in turn, are proportional to the initial concentrations. The situation of the mixed HIPE containing similar numbers of A and B water drops held at fixed but random relative locations by the weak gel nature of the HIPE is shown schematically in Figure 1. In general, A and B initially located in separate droplets can meet and react together by combination of water drop coalescence and dissolution in and diffusion across the surfactant-coated oil films separating the water drops. Dependent on the HIPE composition, the oil films separating the droplets may or may not contain excess surfactant in the form of aggregated species including either inverse microemulsion droplets or lyotropic liquid crystalline phases⁵. The presence of such surfactant aggregates may solubilise transporting A molecules in the oil and hence cause facilitated transport of A across the oil films. A further complication can arise from the fact that, in addition to the mass transport of the species A, it is expected that mass transport of water between the emulsion drops will also occur due to osmotic pressure differences between the two droplet types.

As will be shown later, the experimental systems can be manipulated to suppress contributions arising from water drop coalescence, facilitated mass transport by surfactant aggregates present in the oil films and water mass transport. We consider here the limiting, idealised situation in which t* is determined solely by a process in which the uncharged species A partitions into, and diffuses across the oil films separating the drops. It is assumed here that the adsorbed surfactant films coating the oil films play no significant role in controlling the rate of permeation of A between droplets. Under these idealised conditions, the permeation in the mixed HIPE structure is equivalent to a system comprising an aqueous donor compartment initially containing species A at concentration CM separated from an aqueous receiving compartment (containing zero A initially) by a liquid oil membrane of thickness h. The area of the oil film A (per unit total volume of the emulsion) is approximately half that of the area of the water drops. Neglecting the distortion of the drops from sphericity gives an approximate expression for A.

_ 3(l - & )

(1) An approximate expression for the average oil film thickness h in terms of the oil volume fraction and mean drop radius r (corresponding to undistorted, spherical drops of the same volume as the actual distorted drops present in the HIPE) is then:

h » - (2)

3(1-A)

If it is assumed that the passive mass transport of A is determined solely by diffusion (i.e. that the transfer of A across the oil-water interfaces is not rate-limiting, then application of Fick' s Laws gives the initial (but steady- state) rate of mass transport of the species A across the oil film E as :

E - ^{A VDe}«^K~ (3)

h where D is the diffusion coefficient of the species A in the oil film, V is the total volume of the mixed HIPE and K_ow is the equilibrium partition coefficient of the species A between oil and water (i.e. K_ow = [A] _oii [A] _water at equilibrium) . The time for the indicator colour to change (t*) is the time taken for the transfer of a number of moles of A equal to that required to fully react with all the reagent B present, i.e. a reaction stoichiometric factor (S) times the number of moles of B. In a volume V of the mixed HIPE containing equal volumes of HIPEl and HIPE2, the number of moles of B (n_B) is 2 and hence: t. ₌ V(l-t_o3)c_B1S 2c_B2r² ₀S

2E ~9(\-<>₀)Dc_MK_m

The final equation 5 predicts the time taken for the indicator colour change (t^*) for mixed HIPE emulsions in which :

• equal volumes of HIPEl (containing transferring reagent) and HIPE2 (containing indicator species) have been mixed;

• mass transfer between water drops occurs only by passive diffusion across the oil film separating the drops, i.e. no water drop coalescence occurs and there is no facilitated transport by (for example) reversed micelles of the surfactant in oil;

• within the passive diffusion process, the rate- determining step is the diffusion process across the oil film. The processes of entry and exit of transferring molecules into and out of the oil film are both relatively fast.

Transfer of hydrogen peroxide between water drops in water- in-dodecane HIPEs.

We first discuss measurements of the "trapping time" t* for the transfer of hydrogen peroxide across dodecane oil films into aqueous drops containing potassium permanganate as indicator. Peroxide and permanganate react according to²⁶:

2 MnCV + 5 H₂0₂ + 6 H⁺ -→ 2 Mn²⁺ + 5 0₂ + 8 H₂0

In the mixed HIPE, this indicator reaction produces a loss of the brownish/pink colour of the permanganate to the white appearance of the HIPE in the absence of added indicator. Referring to equation 5, the stoichiometry factor S is 2.5 for this reaction. Measurements of t^* were performed by mixing equal volumes of HIPE1 containing 0.75 volume fraction of aqueous phase containing various concentrations of hydrogen peroxide and HIPE2 containing 0.75 volume fraction of aqueous phase containing 0.1 mM KMnC indicator. Both HIPE1 and HIPE2 and the final mixed HIPE contained 0.25 volume fraction of dodecane as oil continuous phase and were stabilised using 1 wt% of Anfomul 2887 surfactant. As shown later, this surfactant concentration was carefully selected to be the minimum required such that no emulsion drop growth was observed over 2 days, i.e. longer than the timescale of the t^* measurements. Hence, this choice of surfactant concentration is expected to minimise possible peroxide mass transport due to drop coalescence and facilitated transport across the oil films by excess surfactant present in the form of reversed micelles or other aggregates present in the oil.

In order to compare measured t* values with those estimated using equation 5, we require values of the diffusion coefficient of hydrogen peroxide in dodecane (D) and the partition coefficient (K_ow) for hydrogen peroxide between water and dodecane. D was estimated using a literature value of D_w for pentane in water at 25°C of 1.06 x 1CT⁹ m² s^{"1 27} and assuming that D scales as (molar volume)^-0'4, where the scaling exponent was taken to be intermediate between -1/3 (spherical molecules) and -1/2 (random coil chains) . The value was further scaled by the ratio of the viscosity of water at 25°C and of dodecane at 20°C (= 0.8899/1.374 ) ²⁸ to yield a final estimated value of 1.3 x 10^~9 m² s^"1 for hydrogen peroxide in dodecane at 20°C. The value of K_ow for hydrogen peroxide between pure water and dodecane was measured for a range of aqueous peroxide concentrations using the high sensitivity, back-extraction method described in the experimental section. The results, shown in Figure 2, show that K_ow is approximately independent of the peroxide concentration (i.e. non-ideality effects are not significant) and is 1.1 x 10^"7. This value of K_ow is 3-4 orders of magnitude lower than literature values for hydrogen peroxide partitioning between water can various moderately polar oils such as esters, alcohols and ethers^29"

31

The interaction between hydrogen peroxide and urea causes urea addition to the aqueous phase is expected to increase the affinity of peroxide for the water phase and thereby affect Kow. Similarly, addition of a hydrophobic surfactant to the oil phase is expected to increase the affinity of the peroxide for the oil. Using the low-sensitivity method described in the experimental section, we measured the effects on K_ow of urea addition to the water phase and of Anfomul 2887 surfactant addition to the oil phase. From the results summarised in Table 1, we can see that urea addition to the water phase slightly reduces K_ow (and hence should enhance the trapping of peroxide in water droplets) whereas excess surfactant in the oil dramatically increases K_ow. It is likely that surfactant addition to the oil leads to solubilisation of the peroxide within reversed micelles or other aggregates of the surfactant; this effect is expected to cause dramatically reduced trapping times.

Figure 3 compares measured trapping times for HIPEs with (i) no urea, (ii) 2 M urea in only the donor droplets and (iii) 2 M urea in both the donor and receiving droplets with t^* values calculated using equation 5 with D = 1.3 x 10^~9 m² s^"1 and K_ow = 1.1 x 10^~7 for HIPEs with no urea and K_ow = 2 x 1CT⁸ in the presence of urea. We have assumed here that K_ow has the value corresponding to no excess surfactant present in the oil and that K_ow in the presence of 2 M urea but at zero surfactant is reduced by the same factor (5 fold) as measured in the presence of surfactant (Table 1) . For the HIPEs with no urea, the mean drop radius r was 33 μπι for all the peroxide concentrations which corresponds to an approximate mean oil film thickness (equation 2) of 7.3 um. For the urea-containing systems, the mean drop radius varies from 9.8 (at low peroxide cone.) to 21 (at high peroxide cone. ) which correspond to oil film thicknesses ranging from 2.2 to 4.7 μπι. As seen in Figure 3, the measured values of t^* and their variation with peroxide concentration and urea addition show reasonable agreement with the approximate values calculated using equation 5. Equalising the urea concentrations in both the donor and received droplets (expected to minimise water transport rates due to osmotic pressure differences) does not produce a large change in trapping time. The trapping times predicted according to equation 5 correspond to the longest times possible since the model assumes mass transfer occurs only by passive diffusion with no contributions from either emulsion drop coalescence or from facilitated transport of peroxide across the oil films by surfactant aggregates. Hence, the value of t* measured in HIPEs containing different concentrations of Anfomul 2887 surfactant should exhibit a maximum when plotted versus surfactant concentration. At low surfactant concentrations which are too low to stabilise the drops against coalescence, the drop coalescence will act to reduce t^*. At high surfactant concentrations such that excess surfactant is present in the continuous oil phase, the excess surfactant (probably in the form of reversed micelles) is expected to strongly increase K_ow by solubilisation and hence reduce t^* by facilitated transport. Figure 4 shows the variation of t* with Anfomul 2887 surfactant concentration for HIPEs containing hydrogen peroxide as transporting species, potassium permanaganate as indicator which also contain 2 M urea in the donor droplets. As predicted, it can be seen that t^* passes through a maximum which occurs at a surfactant concentration of around 1 wt% for the different peroxide concentrations. The mean emulsion drop radii were measured for these systems, both immediately after preparation and after incubation for 27 hours. The lower plot of Figure 4 shows the mean drop radius data for the emulsions containing 5 mM hydrogen peroxide. The initial mean drop radius decreases progressively with increasing surfactant concentration. Significant drop growth by coalescence occurs over 27 hours for emulsions containing less than 1 wt% surfactant whereas no drop growth is observed for higher surfactant concentrations. There is good agreement between the surfactant concentration producing the maximum t* and the minimum concentration required to suppress drop growth. The drop radius plots for the other peroxide concentrations (not shown) behave similarly. As discussed above, the reduction in t* with increasing surfactant concentration (above that corresponding to the maximum in t*) may be due to a mass transport contribution from facilitated transport. However, increased surfactant concentration also leads to a reduction in mean drop radius which, as seen by inspection of equation 5, will also contribute to a reduction in t^* in this surfactant concentration range.

Transfer of HC1 and NaClO between water drops in HIPEs.

We investigated the transfer of HC1 using receiving drops containing 0.024 m methyl orange as indicator. This indicator, in water drops at an initial pH of 6, undergoes a colour change from orange to red as the pH is reduced below its pKa of 3.75 by mass transfer of the HCl . The transfer of NaClO was measured using indicator drops containing 0.017 Congo Red initially acidified to pH = 3. Mass transfer of NaClO (a weak base) produces a colour change from blue to red when the pH of the Congo Red droplets is increased to a value above the indicator pKa of approximately 4. Measured trapping times for these ionic transferring species are compared with those for hydrogen peroxide (uncharged) in Figure 5. Two conclusions can be drawn from these results. Firstly, the peroxide trapping times in these HIPEs stabilised by the surfactant 0₂G₂ are similar to those in HIPEs stabilised by Anfomul 2887 (see Figure 3) . Secondly, and more surprisingly, the mass transfer rates of the ionic species HCl and NaCIO across the oil films are of a similar order of magnitude to the rates for the uncharged species hydrogen peroxide. If, as is commonly assumed, the partitioning of ionic species between water and oil is negligible, then it is expected that ionic species should remain trapped indefinitely. Because the mass transport rates are primarily determined by the oil-water partition coefficient, the results here suggest that the values of K_ow for HCl and NaCIO between water and dodecane are of a similar order of magnitude to that for hydrogen peroxide (10^"7). The limited partition coefficient data available for ionic solutes distributing between water and apolar oils suggests that this conclusion is indeed valid. For example, K_ow for HCl partitioning between benzene and water is 8 x 10^{" 6} for an aqueous concentration of 0.34 M³¹. K_ow for CsCl partitioning between toluene and water is 1 x 10-6²⁰.

The effect of changing the oil volume fraction in the mixed HIPEs on the trapping time of 5 mM HCl with methyl orange as indicator. As seen in Table 2, for a series of HIPEs with approximately constant mean water droplet sizes, increasing φ₀ increases the mean thickness of the oil films separating the water droplets and hence increases t^*. We have investigated a strategy to increase the trapping time for ionic species. For the NaClO/Congo Red system, the CIO^" species is anionic and the Congo Red indicator bears a formal charge of either 2^" (at high pH) or 1^" (at low pH) . Even though the actual species transferring across the oil film is likely to be an uncharged ion pair, we hypothesised that changing the adsorbed surfactant layer stabilising the oil films from non-ionic to negatively charged should produce electrostatic repulsion between the film and the anions and might lead to a reduced transfer rate. In Figure 6, trapping times for the NaClO/Congo Red system in HIPEs stabilised by the non-ionic surfactant O2G2 (non-ionic) are compared with those for HIPEs stabilised by O2G2 "doped" with the anionic surfactant AOT . It can be seen that the negatively-charged surfactant does increase t^*, i.e. the mass transfer rates are reduced.

Finally, we note some additional experimental observations on these systems.

• We were able to prepare stable HIPEs using 0.65 cSt PDMS as oil with O2G2 as stabilising surfactant. Trapping times for the HCl/methyl orange system in PDMS

HIPEs were generally found to be significantly lower than for corresponding systems with dodecane as oil. The explanation for this effect could be that K_ow is increased for PDMS as but it was observed that the water-in-PDMS emulsion drops were mutually adhesive, i.e. flocculated. Droplet adhesion is expected to produce oils films which are thinner than predicted by equation 2 and hence this effect is likely to contribute to shorter trapping times.

· Attempts to prepare stable HIPEs with either squalane or triglyceride (rapeseed oil) as the oil phase using either O2G2 , Anfomul 2887 and various other hydrophobic surfactants were unsuccessful. Hence, it remains to be determined whether longer trapping times can be achieved using alternative oil phases. Conclusions

We have used HIPEs to compartmentalise hydrophilic reagents within water droplets separated by micron-thickness oil films and successfully developed a simple visual colour change method to determine the time required for mass transport of the species between water compartments. Measured trapping times for the transport of hydrogen peroxide across dodecane films in mixed HIPEs show reasonable agreement with approximate calculated values based on a model of partitioning of the peroxide into the dodecane followed by rate-limiting diffusion across the oil film. Measured trapping times depend on the concentrations of the aqueous species undergoing transport, emulsion drop sizes and composition and are reduced when the emulsions are unstable with respect to water droplet coalescence. A surprising result is that trapping times are of similar magnitudes for both uncharged species such as hydrogen peroxide and charged reagents such as H⁺ and CIO^".

Table 1. Variation of the partition coefficient of hydrogen peroxide between water (with and without 2 M urea) and dodecane with the concentration of Anfomul 2887 surfactant.

Table 2. Variation of trapping time t* with oil volume fraction for water-in-dodecane HIPEs containing 5 mM HCl and 0.024 mM methyl orange indicator. HIPEs were stabilised by 8 mM 0₂G₂ and prepared by hand shaking except for the emulsion marked + which was stabilised by 16 mM Q₂G₂ and prepared using a paddle stirrer.

Figure 1. Schematic of a mixed water-in-oil HIPE consisting of water droplets containing the transferring species (white) , indicator species (coloured red before reaction and white after reaction) separated by films of the oil continuous phase (green) . The inset shows a blow-up of an oil film (mean thickness h) separating white and red droplets. Sufficient mass transfer across the oil films to produce the red-to-white indicator colour change occurs in the measured trapping time t* and produces an overall colour change of the HIPE.

Figure 2. Variation of partition coefficient of hydrogen peroxide between water and dodecane with aqueous phase peroxide concentration. Figure 3. Comparison of measured and calculated values of trapping time t* for the transfer of hydrogen peroxide between water drops in water-in-dodecane HIPEs containing 0.25 volume fraction of dodecane and stabilised by 1 wt% of Anfomul 2887 surfactant.

Figure 4. Upper plot: variation of t* with Anfomul 2887 surfactant concentration for water-in-dodecane HIPEs with 0.25 volume fraction of dodecane, hydrogen peroxide as transporting species (concentrations indicated in the legend) and potassium permanganate as indicator. The donor drops contained 2 M urea. Lower plot: mean drop radius versus surfactant concentration for HIPEs containing 5 mM hydrogen peroxide at time = 0 and 27 hours. Figure 5. Trapping time t* for the compartmentalisation of

HCl, NaCIO and hydrogen peroxide in water-in- dodecane HIPEs containing 0.25 volume fraction of oil and stabilised by 16 mM 0₂G₂. The mean drop radius was around 6 μπι in all cases which corresponds to a mean oil films thickness of approximately 1.3 um. The emulsions were stable with respect to drop growth over 27 hours except for those containing 2 M peroxide and 2 M HCl. Figure 6. Trapping time t* for the compartmentalisation of CIO^" and acidified Congo Red water-in-dodecane HIPEs containing 0.25 volume fraction of oil and stabilised by either 16 m 0₂G₂ (non-ionic) or 14 mM 0₂G₂ + 2 mM AOT (anionic) . The mean drop radius was around 6 urn in all cases which corresponds to a mean oil films thickness of approximately 1.3 μιτι. The emulsions were stable with respect to drop growth over 27 hours except for the AOT- containing HIPEs with the two lowest NaClO concentrations.

Claims

1. A cleaning composition comprising a water-in-oil emulsion, having a plurality of independent aqueous phases, wherein an aqueous phase comprises a bleaching agent.

2. A cleaning composition comprising a water-in-oil emulsion, having a plurality of independent aqueous phases, wherein a substantially water insoluble bleaching agent is suspended in an aqueous phase or an oil phase.

3. A composition according to claim 1 or 2, wherein composition comprises a bleach activator.

4. A composition according to claim 1, 2 or 3, wherein a bleaching agent is hydrogen peroxide, PAP or a per-salt such as perborate, percarbonate, persulphate.

5. A composition according to claim 4, wherein the connect ration of the hydrogen peroxide is typically from 0.1 to

50%, e.g. 15%.

6. A composition according to any one of claims 1 to 5, wherein the aqueous phase comprises at least 40% by weight of the composition, preferably at least 50% by weight, more preferably at least 60%, more preferably at least 70% and most preferably at least 75% by weight of the composition.

7. A composition according to any one of claims 1 to 6, wherein the oil phase preferably comprises at least 5%, more preferably at least 10% and most preferably about 25% by weight of the composition.

8. A composition according to any one of claims 1 to 7 , wherein the oil phase comprises a mineral oil / hydrocarbon such as a paraffin / kerosene.

9. A method of preparation of a composition according to any one of claims 1 to 8, comprising the formation of a plurality of independent water-in-oil emulsions and mixing same together under low shear conditions.

10. The use of a cleaning composition according to any one of claims 1 to 8 in a cleaning operation.