WO1998053883A1

WO1998053883A1 - Microemulsion compositions

Info

Publication number: WO1998053883A1
Application number: PCT/GB1998/001525
Authority: WO
Inventors: Norman Govan
Original assignee: The Secretary Of State For Defence
Priority date: 1997-05-29
Filing date: 1998-05-26
Publication date: 1998-12-03
Also published as: AU7543498A; GB9710933D0

Abstract

Decontamination compositions, particularly for removing chemical warfare reagents are described. These compositions comprise a reagent which reacts and deactivates a toxic chemical, a first solvent such as an oil, a second solvent such as water in which the first solvent is immiscible and a surfactant which is in the form of a microemulsion. Concentrates lacking the second solvent which can be diluted in situ to produce the decontamination composition are also described and claimed. Preferred surfactants include sodium dodecylsulphate (SDS) and Triton X100. Methods for decontaminating surfaces by applying the above-described compositions are also described.

Description

Microemulsion Compositions

The present invention relates to microemulsion compositions, in particular microemulsion compositions which are useful in the decontamination of surfaces. These compositions are able to remove noxious or toxic chemicals or reagents such as chemical warfare (C ) agents.

Liquid decontaminants are used for the decontamination of CW agents on small to medium scale equipment and vehicles.

Currently used liquid decontaminants are aqueous based systems that inactivate CW agents effectively, but has a number of shortcomings. The most serious of its failings is that the decontaminant is corrosive to light metal alloys and must be used within 30 minutes of being prepared. Furthermore, to be wholly effective, particularly against thickened and entrapped CW agents, the decontaminant requires to be vigourously brushed onto the contaminated surface. This makes decontamination a time consuming, labour intensive and logistically demanding process.

There is therefore a need for a more universally applicable, aqueous based decontaminant with a reduced logistical burden.

According to the present invention there is provided a concentrate comprising a reagent which reacts with and deactivates a toxic chemical, a first solvent and a surfactant wherein said concentrate forms a decontaminant composition in the form of a microemulsion when mixed with a second solvent which is immiscible with said first solvent.

The concentrates of the invention can be mixed with second solvent on site and used directly. Suitably one of the first or second solvents is a water immiscible oil and the other is water. Where the first solvent is water and the second solvent is an oil, the concentrates will form a water-in-oil microemulsion which may be particularly effective in the decontamination process.

For many applications however, it may be preferred that the second solvent is water, as this may be provided by local supplies in the vicinity where the decontamination procedure is to be effective, for example on a battlefield, thus reducing the need to transport large volumes of liquid. It has been found that impure water sources, even sea water is a suitable second solvent .

Suitably the concentrate is one which will form a decontaminating microemulsion composition when mixed with from 70 to 90%w/w of second solvent, preferably between in excess of 78% w/w second solvent.

Thus the invention further comprises a decontaminant composition comprising a reagent which reacts with and deactivates a toxic chemical, a surfactant , a first solvent which is immiscible in second solvent , and at least 78%w/w of said second solvent, said composition being in the form of a microemulsion.

As used herein the term " microemulsion" refers to a fluid dispersion of two immiscible liquids and a surfactant that exist in a single phase. Microemulsion droplet sizes are very small typically 10-50nm. Macroscopically they appear as optically clear fluids because the scattering of light is very low. Unlike macroemulsions, microemulsions form spontaneously and are thermodynamically stable. The dynamic properties of microemulsions can allow solubilisation of both polar and non- polar materials in the same medium. For instance, they have an ability to dissolve both water and oil based materials.

The first solvent is suitably a water- immiscible oil in which the said toxic chemical is at least partially soluble. For many CW agents, toluene, isooctane, cyclohexane or cyclohexanone are suitable first solvents . The first solvent will generally be present in an amount of from 5 to 20%w/w in the concentrate, so that it will be present in an amount of from l-5%w/w in the microemulsion composition.

Suitable surfactants are those which allow the formation of microemulsions. Microemulsions may be visualised as dispersions of very small droplets of water-in-oil (W/O) or oil-in-water (O/W) separated by a layer of surfactant (see Figure 1 hereinafter) . The surfactants may be non-ionic or ionic, but when ionic surfactants are used, the further inclusion of a co-surfactant may be desirable in order to lower the interfacial tensions sufficiently to allow microemulsion formation. Particular examples of surfactants for use in the concentrates and compositions of the invention are sodium docecylsulphate (SDS) , Triton DF16 (TDF) , Triton- X100(TX), cetyltrimethylammonium chloride (CTAC) , Synperionic L4 (SYNP) , Atlas G4829 (ATL) and cetyltrimethlammonium hydroxide (CTAOH) , and the sodium salt of dioctylsulphosuccinate (AOT) . The surfactant is suitably present in an amount such that in the final composition, it is present in an amount of from 1 to 30%w/w.

Suitable co-surfactants include alchohols such as propanol and butanol . The surfactant : co-surfactant ratio is suitably in the range of from 1:4 to 2:1 w/w in the microemulsion composition. From the viewpoint of saving cost and for logistical purposes, it is preferred that the amount of surfactant and/or co- surfactant used in the microemulsion is kept as low as possible. It has been found that the use of mixed surfactants can reduce the amount of total surfactant required to form a stable microemulsion and thus this forms a preferred embodiment of the invention. In particular, the surfactant mixture contains a non- ionic and an anionic surfactant. Particularly preferred mixtures include SDS and TX, TDF and AOT and TDF and SDS.

The optimum ratio of the two immiscible phases will vary to a certain depending upon the nature of the liquids used as illustrated hereinafter. The skilled person would be able to determine these using routine methods as illustrated hereinafter.

Preferably the microemulsion formulation utilised has a good degree of thermal stability at temperatures between 5 and 30°C, and preferably between -15 and 50°C. The thermal stability of the microemulsion formulation may be tested using routine methods as illustrated hereinafter.

Optionally the concentrates and compositions of the invention may further include anti-freeze compounds such as ethylene glycol in order to increase the temperature range over which the microemulsions are stable.

The concentrates and compositions may also contain viscosity modifying agents such as thickeners, suitably in an amount of up to 3%w/w. A thickener formulation may improve the decontamination efficiency of the composition, particularly when applied to vertical or inclined surfaces. Suitable viscosity modifying agents include water soluble polymers such as Acrysol SCT 275, Acrysol RM 202, Ucar 106 polyphobe heurase, Ucar 104, Natrosol pluss GR331, polyvinylpyrrolidone (PVP) for example of molecular weight from 10,000 to 700,000, in particular PVP 10,000, PVP 360,000 or PVP 700,000, hydroxymethylcellulose, Aculyn 22, or copolymers such as copolymers of methyl vinyl ether and maleic anhydride cross- linked with 1, 9-decadiene (PVM/MA decadiene cross polymer) such as those sold under the trade name Stabilieze 06 or Stabilieze QM.

Other suitable viscosity modifying agents include colloidal silica and natural gums.

A preferred thickening agent, identified by rheology studies, are the Stabilieze polymers, in particular Stabilieze 06. Decontaminant compositions thickened with these polymers exhibited good shear thinning behaviour and were demonstrated to remain stable after being subjected to high shear mixing.

Suitable active reagents are those which react with and neutralise toxic agents in particular CW agents. Although many reactions can detoxify CW agents, preferably those used in the context of the present invention are reactions which occur under mild reaction conditions. The active reagents should suitably be relatively stable. Nucleophilic substitution and/or oxidation are preferred decontamination reactions and thus the active reagents are suitably nucleophilic or oxidising agents.

Particular examples of active reagents include bases in particular strong bases such as hydroxides such as alkali metal hydroxides in particular sodium hydroxide, and ammonium hydroxides (NaOH) such as cetyltrimethyl ammonium hydroxide (CTAOH) , oxidising agents in particular hypochlorites such as the alkaline or alkaline earth metal hypochlorites such as calcium hypochlorite (Ca(OCl)₂, sodium hypochlorite (NaOCl) and lithium hypochlorite or hypochlorous acid (HC10) , N-chloramine compounds like sodium dishloroisocyanuric acid (Fichlor) , iodosobenzoic acid (IBA) , basic hydrogen peroxide systems for example including a hydroperoxide anion (H0₂ ^") such as sodium percarbonate (NaC0₃.1.5H₂0₂) or organic peroxyanions such as magnesium monoperoxphthalic acid (MMPA) or other oxidants such as the commercially available oxidant oxone (a mixture of three salts 2KHS0₅/KHS0₄/K₂S0₄) or transition metal complexes able to catalyse the hydrolysis of G-type organophosphates (as illustrated by R.W. Hay et al . , Polyhedron, 15 2381-2386 (1996) in particular transition metal complex catalysts selected from copper, zinc and cobalt complexes such as copper (II) micelles, zinc micelles and cobalt micelles. Other suitable catalytic compounds are manganese or vanadium catalysts, for example [Mn₂L₂ (CH₃C0₂) O] (C10₄)₂ where L is a ligand such as 1, 4 , 7-trimethyl-l, 4 , 7 , -triazocyclononane or VO(acac)₂ where ' acac' represents acetylactonate, which are used in the presense of a preoxide such as t-butyl hydroperoxide .

Preferably, for use in the compositions of the invention, the active reagents are selected from sodium tetraborate, Fichlor, IBA, NaOCl and LiOCl .

Active reagents may be used singly, but more than one active reagent may be incorporated, particularly where the active reagents act synergistically together to bring about a decontamination reaction.

The active reagents selected for use in the concentrates and compositions of the invention are those which have a reasonable degree of solubility in the particular microemulsion system selected. By reasonable is meant that the resultant composition will contain a sufficient amount of active reagent to produce a successful decontamination reaction. In general, this will mean that the compositions should contain from 0.5% to 20% w/w active reagents.

Preferably, the pH of the compositions of the invention will be less than 11 and preferably in the range of from 6 to 9 in order to minimise corrosion of metal surfaces to which it may be applied.

The surface tension of the composition will reflect the ability of the systems to wet a given surface and penetrate capillaries. The lower the surface tension a liquid possesses, the greater its ability to wet a surface and penetrate capillary traps. Preferably therefore, the surface tension of the compositions of the invention are lower than or equal to that of the toxic chemical which is to be neutralised. The surface tension of CW agents are as follows: HD - 42.50; GD - 24.50 and VX -31.30. Thus the surface tension of the composition of the invention are suitably at least of the same order and preferably less than these values depending upon which CW agent is faced. This will reduce the amount of agitation or scrubbing which is required for effective removal of CW agent.

In addition to the above constraints, the composition of the invention is preferably robust in the sense that they are not at or near a phase boundary which may make them sensitive to changes in conditions. This can be tested using phase evolution studies as illustrated below. The precise concentrations of the two immisible liquids may be adjusted in order to ensure that the microemulsion forms a stable one phase microemulsion. The invention further provides a method for decontaminating a surface to remove a toxic chemical, said method comprising applying to said surface a decontaminant composition as described above. The surfaces may be the metal, plastics or painted surfaces, for example of military vehicles etc..

Compositions of the invention may be applied in various ways. For example they may be poured or sprayed onto a contaminated surface, or example using lances or other known spray equipment. The first and second solvents may be pre-mixed or they may be combined together so as to form the microemulsion within in the application apparatus such as a lance.

Where necessary brushing or other abrasive methods may be applied in order to ensure complete decontmination is effected.

The invention will now be particularly described by way of example with reference to the accompanying diagrammatic drawings in which:

Figure 1 is a schematic representation of an oil-in-water microemulsion droplet stabilised by a long-chain surfactant and an alcoholic co-surfactant; and

Figures 2-4 are phase evolution diagrams for microemulsion formulations of the invention. Example 1

Properties of Microemulsion Compositions

The following microemulsion compositions were prepared:

Table 1

Unlike conventional emulsion systems, microemulsions are thermodynamically stable and will remain as a single phase dispersions indefinately. The stability of the microemulsions of Table 1 was tested at 20°C for periods up to 12 months. As expected, when stored in this way, all of the candidate microemulsions remained completely stable throughout the evaluation period.

Thermal stability of the microemulsions was tested over the temperature range of -15 to 50°C. Vials containing the microemulsions were placed into a temperature controlled bath at the desired temperature and visually examined for any changes in phase behaviour. These experiments were carried out at each of 5° increments over the 15 to 50°C range. Each system was allowed to equilbrate for at least two hours before observations were recorded. The thermal stability range for the microemulsions systems of Table 1 are shown in Table 2.

Table 2

Three of the nine microemulsion systems (1, 4 and 6) remained completely stable across the entire temperature range. Microemulsion 1 was exceptionally stable to extreme temperature fluctuation and did not break down even when heated to 75°C and the shock cooled to -10°C. The addition of ethylene glycol (anti-freeze) up to 10%v/v did not appear to reduce the thermal stability of these systems.

The surface tension of selected microemulsions was measured using a platinum ring and a Kruss processor tensiometer, thermostated at 25°C. The values reported in Table 3 hereinafter are an average of eight measurements .

Table 3

All of the above-mentioned microemulsions have surface tensions lower than HD and VX and are of the same order of magnitude as GD. This should allow the microemulsions to access small capilliaries and destroy entrapped agent.

In order to assess the phase evolution of each surfactant system, samples were prepared at a constant surfactant concentration the the oil to water ratio was increased uniformly. The samples were then studied systematically as a function of temperature.

Representative phase evolution diagrams for three of the microemulsions (1-3 in Table 1 hereinafter) are illustrated in Figures 2, 3 and 4 respectively.

The diagrams show increasing temperature on the y-axis against increasing oil phase and decreasing aqueous phase on the x- axis. The broken lines on the plot indicate phase boundaries. The symbols lΦ and 2Φ indicate the number of phases present, i.e. 2Φ indicated that the sample has two distinct layers at the given temperature and oil/water ratio. The subscript μE indicates where a microemulsion has formed and the subscript L indicates a lamellar system. The hatched area of the phase diagram shows the region where the systems form a stable one phase microemulsion.

TDF is a linear nonionic surfactant of the Triton series that is reported to be biodegradable. It is a slightly viscous fluid that disperses readily in water. Preliminary studies identified that at least 15%w/w TDF was required to form microemulsions. The system was studied at 15% and 20% w/w TDF using toluene and isooctane as the respective oil phase. Representative phase evolution diagrams for the TDF/toluene and TDF/isooctane are illustrated in Figures 2 and 3. The diagrams show that high aqueous phase volume microemulsions are formed in both systems . At room temperature the toluene and isooctane systems behave in a similar manner. However, the systems behave quite differently to changes in temperature and formulation, as can be seen from the size of the relative microemulsion regions and number of boundary changes in the respective phase diagrams. Clearly, microemulsion formulation 3 containing 2% isooctane is more stable than formulation 2 containing toluene.

SDS is an anionic surfactant. In its pure form SDS is a white powder that requires vigorous shaking to dissolve in water. Ionic surfactants of this type normally require a co- surfactant to form an oil-in-water microemulsion. The phase evolution studies identified formulation 1 in Table 1 to be the most stable over the entire region of study.

The solubility and stability of a range of active reagents in the above microemulsions was investigated by adding aliquots of the reagents with stirring to vial containing 15ml of microemulsion at room temperature. The capacity of each microemulsion was deemed to have been reached when sedimentation occurred or the microemulsion phase separated. The results of these studies are shown in Table 4

Table 4

Active Solubility of active reagents in Reagent microemu1sion systems (%w/v)

1 4 3 7 5 6 8/9

Ca(OCl)₂ <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

NaOCl 3.1 11.3 2.3 1.9 17.5 14.4 -

LiOCl 3.3 12.4 4.2 1.2 12.9 11.7 -

Fichlor 8.1 21.0 9.7 5.5 10.1 9.6 4.0

IBA 0.6 0.4 0.2 0.4 0.3 - 0.5

MPPA >32.0 5.3 13.8 5.7 22.9 - -

Oxone 8.0 11.5 4.6 - 7.5 - -

NaC0₃H₂0₂ 2.3 2.9 1.4 - 3.6 - - Example 2

Reactivity of Microemulsions to CW agents

The ability of a selection of microemulsions containing a range of active reagents to inactivate the chemical warfare agents HD, GD and VX was tested by carrying out a series of decontamination reactions. CW agent (250μl) was added with stirring to the test microemulsion solutions (generally 15ml) . Unless the system was found to be catalytic in nature, the reaction mixtures usually contained a two fold excess of reactive component over the agent. [Catalytic effect was assessed by carrying out a decontamination reaction with an excess of CW agent; if at the end of the reaction, the reaction had gone to completion and no CW agent remained, a catalytic effect was assumed.]

Decontamination reactions were followed by FTIR spectroscopy on an Applied Systems reaction analysis system. The system was fitted with a diamond ATR reaction probe, nichrome wire source and an MCT detector. Rapid data collection was required, since the majority of the reactions were so fast. This was achieved using the " rapid reaction" macro, where the resolution was reduced to 16cm^"1 and the signal averaged over 4 co-added scans. Apodization was set on the Happ-Genzel function. In a typical REact IR monitored decontamination experiment, 15ml of microemulsion was used and this volume was the minimum required to ensure that complete submersion of the ATR probe was achieved.

CW agent degradation were confirmed by either NMR or GC analysis. Tables 5 and 6 summarise the observed reaction time obtained for selected microemulsion systems containing a range of reactive components. Table 5

* ME represent " Microemulsion"

Table 6

As can be seen from the above tables, certain active reagents are better than others with regard to certain toxic chemicals. ■ The selection of an appropriate active reagent will therefore depend to a certain extent upon the nature of the toxic chemical being removed and will be apparent to the skilled chemist .

Example 3

Decontamination Studies In order to evaluate the decontamination efficiency of the decontaminant compositions, painted test panels (of surface area of 10.0cm³) were contaminated with lOμl of CW agent at a surface contamination density of approximately lOg^"2. The contaminated panel was then placed in a sealed petri dish of about the same cross sectional area as the panel for 30 minutes. About 10ml of test liquid decontaminant was added to each petri dish so as to completely wet the surface of the panel . After the panel was exposed to the decontaminant for a further 30 minutes, the liquid decontaminant was removed from the petri dish. Any CW agent left on the panel was then extracted into propanol . The extracts were then analysed by GC for quantitative determination of the residual CW agent left on the panel. For each test system, at least three experiments were conducted on three separate but identical plates. Tables 7 and 8 below summarise the removal efficiency results obtained for each of the compositions against GD, HD, VX and THD (thickened mustard) contaminated plates. For comparative purposes, the known decontaminant (CAD) was included.

Tests were performed on panels covered with non-sorptive two pack polyurethane green matt finish panels . The reduce the number of variables, all the panels were painted with the same polyurethane paint which is resistant to agent penetration. Control experiments showed that all of the CW agent was present on the surface without any loss as a result of diffusion into the paint. The results are shown in Table 7.

In addition some systems were tested on sorptive alkyd paint and the results are shown in Table 8.

Table 7 Decontamination Efficiency of Decontaminant compositions on non-sorbant painted polyurethane plates

Table 8 Decontamination Efficiency of Decontaminant Compositions on sorbant alkyd painted plates

As shown in Table 7, all of the compositions of the invention removed both neat and thickened CW agents more effectively than CAD. Furthermore, compositions without active reagents were ineffective at removing CW agents from the test plates.

Example 4

Microemulsion Decontamination Systems

The following compositions are examples of compositions of the invention.

Composition 1 Components % by weight

Water 77.9

Sodium dodecylsulphate 10.4 Butanol 9.3

Cyclohexane 2.4

To this base formulation is added:

Sodium tetraborate (borax) 2. Ow/v Fichlor 5. Ow/v

Iodosobenzoic acid 0.5w/v

Composition 2

Components % by weight

Water 77.9

Sodium dodecylsulphate 10.4

Butanol 9.3

Cyclohexane 2.4

To this base formulation is added:

NaOCl 9.9v/v Composition 3

Components % by weight

Water 77.9 Triton X100 18.5

Isooctane 2.5

To this base formulation is added:

LiOCl lOw/v

Composition 4

Components % by weight

Water 69.95

Sodium dodecylsulphate 9.24

Butanol 8.20

Toluene 4.32

Fichlor 4.53

Borax 1.80

IBA 0.46

Stabilieze 06 2.50

Composition 5

Component %w/w

Water 70.70

Sodium dodecylsulphate 9.48

Butanol 8.42

Cyc1ohexanone 4.43

Fichlor 4.64

Borax 1.86

IBA 0.47

Claims

1. A concentrate comprising a reagent which reacts with and deactivates a toxic chemical, a first solvent and a surfactant wherein said concentrate forms a decontaminant composition in the form of a microemulsion when mixed with a second solvent which is immiscible with said first solvent.

2. A composition comprising a concentrate according to claim 1 which further comprises said second solvent and is in the form of a microemulsion.

3. A composition according to claim 2 wherein said second solvent is water.

4. A compostion according to claim 1 or claim 2 which comprises from 70 to 90%w/w of said second solvent.

5. A concentrate according to claim 1 or composition according to any one of claims 2 to 4 wherein the said first solvent is a water-immiscible oil in which a CW agent is at least partially soluble.

6. A concentrate or composition according to claim 5 wherein the said first solvent is selected from toluene, isooctane or cyclohexane.

7. A composition according to any one of claims 2 to 6 wherein the said first solvent is present in an amount of from l-5%w/w.

8. A concentrate according to claim 1 or composition according to any one of claims 2 to 7 wherein the surfactant is selected from sodium docecylsulphate (SDS) , Triton DF16 (TDF) , Triton X100 (TX) , cetyltrimethylammonium chloride (CTAC) , Synperionic L4 (SYNP) , Atlas G4829 (ATL) and cetyltrimethlammonium hydroxide (CTAOH) .

9. A concentrate according to claim 1 or composition according to any one of claims 2 to 8 which comprises a mixture of surfactants.

10. A concentrate or composition according to claim 9 wherein the mixture comprises a nonionic and anionic surfactant.

11. A concentrate or composition according to claim 9 or claim 10 wherein the surfactant mixture comprises SDS and TX, or TDF16 and AOT or TDF and SDS.

12. A composition according to any one of claims 2 to 11 wherein the surfactant is present in an amount of from 1 to 30%w/w.

13. A concentrate according to claim 1 or a composition according to any one of claims 2 to 12 which further comprises a co-surfactant .

14. A concentrate or composition according to claim 13 wherein the co-surfactants is propanol or butanol.

15. A composition according to any one of claims 2 to 14 which is thermally stable between -15 and 50┬░C.

16. A concentrate according to claim 1 or composition according to any one of claims 2 to 15 which further comprises an anti-freeze compound.

17. A concentrate according to claim 1 or a composition according to any one of claims 2 to 16 which further comprises a viscosity modifying agent.

18. A concentrate or composition according to claim 17 wherein the viscosity modifying agent is a water soluble polymer, colloidal silica or a natural gum.

19. A concentrate or composition according to claim 18 wherein the viscosity modifying agent is a water soluble polymer.

20. A concentrate or composition according to claim 18 wherein the water soluble polymer is a copolymer of methyl vinyl ether and maleic anhydride cross-linked with 1,9- decadiene .

21. A concentrate according to claim 1 or a composition according to any one of claims 2 to 20 wherein the active reagent is a nucleophilic or oxidising agent.

22. A concentrate or composition according to claim 21 wherein the active reagent is one or more reagents selected from sodium tetraborate, Fichlor, IBA, NaOCl and LiOCl.

23. A composition according to any one of claims 2 to 22 which has a pH in the range of from 6 to 9.

24. A composition according to any one of claim 2 to 23 which has a surface tension which is lower than that of said toxic chemical .

25. A method for decontaminating a surface to remove a toxic chemical, said method comprising applying to said surface a composition according to any one of claims 2 to 24 as described above .