METHOD FOR PRODUCING AN AQUEOUS FOAM, AQUEOUS FOAM OBTAINED BY SUCH A METHOD AND USES THEREOF

Abstract

The invention relates to a method for producing an aqueous foam comprising the following steps: (a) preparing a solution comprising at least one surfactant and at least one protic polar solvent, (b) bringing the solution into contact with a pressurised gas, whereby a two-phase mixture is obtained, and (c) injecting the two-phase mixture, whereby, after expansion or dispersion of the gas, the aqueous foam is obtained. According to the invention, the solution further comprises at least one gelling compound chosen from a non-nitrogenous polysaccharide and gelatin. The invention also relates to the aqueous foam obtained by such a method and to the uses of same, in particular in the fields of decontamination, the purification of effluents, or the defusing or containment of explosive devices or suspected explosive devices.

Claims

1. A method for producing an aqueous foam comprising the following steps of: (a) preparing a solution comprising at least one surfactant and at least one protic polar solvent, (b) contacting the solution prepared in step (a) with a pressurised gas, whereby a two-phase mixture is obtained, and (c) injecting the two-phase mixture obtained in step (b), whereby, after expansion or dispersion of the gas, the aqueous foam is obtained, wherein the solution further comprises at least one gelling compound chosen from a non-nitrogenous polysaccharide and gelatine.

2. The production method according to claim 1, wherein the solution further comprises at least one nitrogenous polysaccharide and, optionally, at least one compound enabling the nitrogenous polysaccharide(s) to be dissolved in the solution.

3. The production method according to claim 1, wherein the mass proportions, relative to the mass of the protic polar solvent(s), are: from 1% to 20% of the gelling compound(s) and, optionally, of the nitrogenous polysaccharide(s), from 5% to 25% of the surfactant(s), and from 0% to 10% of the compound(s) enabling the nitrogenous polysaccharide to be dissolved in the solution.

4. The production method according to claim 1, wherein the non-nitrogenous polysaccharide is chosen from agar-agar and carrageenan.

5. The production method according to claim 2, wherein the nitrogenous polysaccharide is a chitosan.

6. The production method according to claim 5, wherein the chitosan has the following structural formula (I): ##STR00002## with a such that 0a1.

7. The production method according to claim 2, wherein the solution comprises at least one compound enabling the nitrogenous polysaccharide(s) to be dissolved in the solution, and the compound enabling said nitrogenous polysaccharide to be dissolved in the solution is chosen from an inorganic acid, an organic acid and a mixture of two or more of these acids.

8. The production method according to claim 1, wherein the protic polar solvent is chosen from water and an alcohol.

9. The production method according to claim 1, wherein the surfactant is chosen from anionic surfactants, cationic surfactants, non-ionic surfactants and mixtures thereof.

10. The production method according to claim 1, wherein the gas implemented in step (b) is chosen from Ar, He, N.sub.2, O.sub.2, H.sub.2, CO.sub.2, N.sub.2O, CH.sub.4 and the mixture of at least two of these gases.

11. The production method according to claim 1, wherein steps (b) and (c) are concomitant.

12. An aqueous foam obtained by the production method according to claim 1.

13. A method of complexing at least one metal in cationic form comprising combining a metal compound with the aqueous foam according to claim 12.

14. The method according to claim 13, wherein the metal is chosen from a transition metal and a lanthanide.

15. A method of decontamination comprising decontaminating an area in need thereof with the aqueous foam of claim 12.

16. The production method according to claim 1, wherein the non-nitrogenous polysaccharide is agar-agar.

17. The production method according to claim 6, wherein a is such that 0.5<a1.

18. The production method according to claim 6, wherein a is such that 0.75a1.

19. The production method according to claim 2, wherein the solution comprises at least one compound enabling the nitrogenous polysaccharide(s) to be dissolved in the solution, and the compound enabling said nitrogenous polysaccharide to be dissolved in the solution is an inorganic acid selected from the group consisting of HCl, HBr, HF, H.sub.2SO.sub.4 and H.sub.3PO.sub.4.

20. The production method according to claim 2, wherein the solution comprises at least one compound enabling the nitrogenous polysaccharide(s) to be dissolved in the solution, and the compound enabling said nitrogenous polysaccharide to be dissolved in the solution is chosen from an organic acid selected from the group consisting of a carboxylic acid having the molecular formula C.sub.mH.sub.2m+1COOH with 0m5 and a dicarboxylic acid having the molecular formula HOOC(CH.sub.2).sub.mCOOH with 0m5.

21. The production method according to claim 1, wherein the protic polar solvent is an alcohol having the molecular formula C.sub.nH.sub.2n+2O, with 1n5.

22. A method according to claim 15, wherein the area in need of decontamination is chosen from a nuclear area; an area of effluents to be purified; an area of explosives, or area suspected of having explosives; devices to be contained; and an area of explosive, or suspected of being explosive, devices to be defused.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0114] FIG. 1 illustrates the evolution, as a function of time (noted t and expressed in min), of the collapse (noted Col. and expressed in %) of the aggregates of the aqueous foams in accordance with the invention M1, M2 and the comparative aqueous foam C1.

[0115] FIG. 2 is a histogram illustrating the distribution in the residual concentration of cations Cu.sup.2+, Zn.sup.2+ and Co.sup.2+ in the drainage liquid phases of the aqueous foams according to the invention M3 and M4, respectively prepared from the solutions S3 and S4, this residual concentration being noted C.sub.r and being expressed as % relative to the initial concentration of these cations in solutions S3 and S4.

DETAILED DISCLOSURE OF PARTICULAR EMBODIMENTS

Assessment of the Stability of Aqueous Foams

[0116] Three aqueous foams, noted M1, M2 and C1, have been produced, M1 and M2 being aqueous foams in accordance with the invention and C1 being a comparative aqueous foam.

[0117] For each of these three foams M1, M2 and C1, the structure as well as the stability have been assessed by the respective measurements of the expansion ratio ER and collapse according to the modalities set forth hereinafter.

[0118] The surfactant implemented is marketed by Eau & Feu company under the reference DP-SF/2. This surfactant DP-SF/2 is formed by a mixture of anionic surfactants (from 1 to 2% mass sodium octylsulphate, from 2 to 3% mass sodium decylsulphate and from 1 to 2% mass sodium laurylethersulphate) and a non-ionic surfactant in water (76-77% mass), propylene glycol (5 to 6% mass) and propylene glycol monobutylether (8 to 9% mass).

Production and Assessment of the Aqueous Foam M1 (According to the Invention)

[0119] In a 500 mL erlenmeyer flask, 20 g of surfactant DP-SF/2, 250 mL of distilled water and then 3.75 g of agar-agar are introduced. The solution, noted S1, is then placed under stirring at a 90 C. temperature until it is fully homogenous. Heating is then stopped and then, when the solution temperature reaches 60 C., the solution S1 is poured into in a 500 mL cream siphon.

[0120] After the siphon is closed, a nitrogen protoxide cartridge is screwed in the location therefor. The siphon is then manually stirred from top to bottom for about 15 seconds for obtaining a homogenous two-phase mixture.

[0121] The siphon is then put upside down (cannula downwards) above a 250 mL graduated cylinder which has been tared beforehand, for calculating the expansion ratio ER.

[0122] The injection of the two-phase mixture is then conducted, by applying a slight pressure to the siphon lever, in the graduated cylinder until a 230 mL height of aqueous foam M1 is reached.

[0123] The filled cylinder is then weighed and the corresponding mass of aqueous foam M1 is determined. The volume of the solution S1 injected is then calculated by dividing the mass of the aqueous foam M1 by the density of this aqueous foam M1 which is 1.0. The expansion ratio ER value is then calculated: ER is 4.1 for the aqueous foam M1.

[0124] The evolution of the height of the aqueous foam M1 is followed over a period of one hour. It is observed that, at the end of one hour, a 30 mL volume of aqueous foam M1 has been lost, which corresponds to a 13% collapse.

[0125] M1 thus has a loose alveolar structure (expansion ratio higher than or equal to 3) and also satisfies the definition of a stable aqueous foam for the purposes of the present invention (collapse lower than or equal to 15%).

Production and Assessment of the Aqueous Foam M2 (According to the Invention)

[0126] In a first erlenmeyer flask, 100 mL of distilled water containing 0.3% mass acetic acid, and then 0.75 g of chitosan from shrimp shell and having an N-deacetylation degree DD higher than 75% are introduced. The whole is then placed under stirring and heated at 80 C. until it is fully homogenised. Then, 2.25 g of agar-agar are added to form a first aqueous solution, which is then heated, under stirring, at 95 C. until it is homogenised. The temperature is then thermally controlled to 80 C. for 1 h.

[0127] In a second erlenmeyer flask, 100 mL of distilled water containing 0.3% mass acetic acid, and then 16 g of surfactant DP-SF/2 are introduced to form a second aqueous solution.

[0128] 100 mL of this second aqueous solution are then introduced in the first erlenmeyer flask. The solution, thus formed by the first and second aqueous solutions, and noted S2, is placed under mechanical stirring (ultra-turax type) until it is fully homogenised. Heating is then stopped and then, when the temperature of the solution reaches 60 C., the solution S2 is poured into a 500 mL cream siphon.

[0129] After the siphon is closed, a nitrogen protoxide cartridge is screwed in the location therefor. The siphon is then manually stirred from top to bottom for about 15 seconds for obtaining a homogenous two-phase mixture.

[0130] As described above, the siphon is then put upside down above a 250 mL (tared beforehand) graduated cylinder.

[0131] Then, the injection of the two-phase mixture is conducted, by applying a slight pressure onto the siphon lever, in the graduated cylinder until a 155 mL height of aqueous foam M2 is reached.

[0132] The cylinder thus filled is then weighed. The volume of solution S2 injected is deduced from the mass measured as previously indicated and the expansion ratio ER value is determined: ER is 3.1 for the aqueous foam M2.

[0133] The evolution of the height of the aqueous foam M2 is followed over a period of one hour. It is observed that, at the end of one hour, a 19 mL volume of aqueous foam M2 has been lost, which corresponds to a 12.2% collapse.

[0134] M2 thus has a loose alveolar structure (expansion ratio higher than or equal to 3) and also satisfies the definition of a stable aqueous foam for the purposes of the present invention (collapse lower than or equal to 15%).

Production and Assessment of the (Comparative) Aqueous Foam C1

[0135] In a 500 mL erlenmeyer flask, 20 g of surfactant DP-SF/2 and 250 mL of distilled water are introduced. The solution, noted SC1, is then placed under stirring until the surfactant is fully dissolved. The solution SC1 is then poured into a 500 mL cream siphon.

[0136] After the siphon is closed and a nitrogen protoxide cartridge is placed, the siphon is manually stirred from top to bottom for about 15 seconds.

[0137] As described above, the siphon is then put upside down above a 250 mL (tared beforehand) graduated cylinder.

[0138] Then the injection of the two-phase mixture is conducted, by applying a slight pressure onto the siphon lever, in the graduated cylinder until a 230 mL height of aqueous foam C1 is reached.

[0139] The cylinder thus filled is then weighed. The volume of solution SC1 injected is deduced from the mass measured as indicated previously and the expansion ratio ER value is determined: ER is 5.7 for the aqueous foam C1.

[0140] The evolution of the height of the aqueous foam C1 is followed over a period of one hour. It is observed that, at the end of one hour, a 58 mL volume of aqueous foam C1 has been lost, which corresponds to a 25.2% collapse.

[0141] If C1 has thus a loose alveolar structure (expansion ratio higher than or equal to 3), C1 does not satisfy the definition of a stable aqueous foam for the purposes of the present invention (collapse markedly higher than 15%).

[0142] The evolution of the collapse of the different aqueous foams M1, M2 and C1, as observed within the hour following their respective deposition in the graduated cylinder, is illustrated in FIG. 1.

[0143] The curves of FIG. 1 clearly highlight that the aqueous foams M1 and M2 according to the invention have a stability markedly higher than the stability of the comparative aqueous foam C1.

Assessment of the Complexing Properties of Aqueous Foams

[0144] Two aqueous foams in accordance with the invention, noted M3 and

[0145] M4, have been produced, the aqueous foam M3 being obtained from solution S3 and aqueous foam M4 being obtained from solution S4.

[0146] To assess the respective complexing properties of these aqueous foams M3 and M4, specific solutions S3 and S4 have been respectively made, wherein a metal salt has been added (here and alternatively, CuCl.sub.2, ZnCl.sub.2 and Co(NO.sub.3).sub.2,6H.sub.2O), so as to reach an initial concentration of metal cation (Cu.sup.2+, Zn.sup.2+ or Co.sup.2+) of 2.5 g/L in solutions S3 and S4.

[0147] The residual concentration of metal cation (Cu.sup.2+, Zn.sup.2+ or Co.sup.2+) in the drainage liquid phase collected over a period of 15 min after forming each of the aqueous foams M3 and M4 has then been assessed, by UV-visible spectroscopy. The comparison of the signal thus obtained with the signals obtained beforehand with standard-solutions enabled this residual concentration to be determined.

Preparation of Solution S3

[0148] In a first erlenmeyer flask, 150 mL of distilled water containing 5% mass acetic acid, and then 1.125 g of chitosan from shrimp shell and having an N-deacetylation degree DD higher than 75% are introduced. The whole is then placed under stirring and heated at 80 C. until it is fully homogenised. 3.375 g of agar-agar are then added to form a first aqueous solution, which is then heated, under stirring, at 95 C. until it is homogenised. The temperature is then thermally controlled at 80 C. for 1 h.

[0149] In a second erlenmeyer flask, 150 mL of distilled water containing 5% mass acetic acid, and then 24 g of surfactant DP-SF/2 are introduced to form a second aqueous solution.

[0150] 150 mL of this second aqueous solution are then introduced in the first erlenmeyer flask. The solution S3 formed by the first and second aqueous solutions is placed under mechanical stirring (ultra-turax type) until it is fully homogenised. Heating is then stopped.

Preparation of Solution S4

[0151] In an erlenmeyer flask, 300 mL of distilled water containing 5% mass acetic acid, and then 24 g of surfactant DP-SF/2 and 4.5 g of agar-agar are introduced. The solution thus obtained, noted S4, is then heated, under stirring, at 95 C. until it is homogenised. The temperature is then thermally controlled at 60 C. for 1 h. Then, heating is stopped.

Assessment of the Complexing Properties to Cu.SUP.2+ of Aqueous Foams M3 and M4

[0152] 100 mL of solution S3 thus prepared are retained in order to make so-called standard-solutions of CuCl.sub.2.

[0153] For this, solution S3 is diluted a first time at 50% by adding 100 mL of distilled water to 100 mL of this solution S3. Then, 1.058 g of CuCl.sub.2 is added to this diluted solution. 200 mL of a stock-solution are obtained which comprises a 2.5 g/L initial concentration of cations Cu.sup.2+.

[0154] Thus obtained stock-solution is then fractioned. A fraction of the stock-solution is preserved whereas the other fractions are diluted, by adding water, so as to obtain working-solutions with respective initial concentrations of cations Cu.sup.2+ of 2 g/L, 1.5 g/L, 1.25 g/L, 1 g/L, 0.75 g/L, 0.5 g/L and 0.25 g/L.

[0155] These different fractions of stock-solution and working-solutions, prepared from solution S3, are then examined by UV visible spectrometry on a wavelength range from 600 nm to 1 000 nm. The absorbance values corresponding to the copper signal are read out so as to obtain a calibration straight line of the concentration of cations Cu.sup.2+ for solution S3.

[0156] The handling procedure and absorbance value measurement method just described are reproduced in the same operating conditions, except for the replacement of solution S3 by solution S4. A calibration straight line of the concentration of cations Cu.sup.2+ is thus also obtained for solution S4.

[0157] 100 mL of solution S3 thus prepared are sampled. To this solution S3, 1.058 g of CuCl.sub.2 are added, so as to obtain a solution with a 5 g/L concentration of cations Cu.sup.2+.

[0158] The solution thus obtained is then poured into in a 500 mL cream siphon. After the siphon is closed, a nitrogen protoxide cartridge is screwed in the location therefor. The siphon is then manually stirred from top to bottom for about 15 seconds for obtaining a homogenous two-phase mixture.

[0159] The siphon is then put upside down (cannula downwards) above an erlenmeyer flask provided with a frit acting as a liquid filter. The injection of the two-phase mixture is then conducted, by applying a slight pressure onto the siphon lever, and a deposit of aqueous foam M3 is obtained on the frit.

[0160] Then, the drainage liquid phase is allowed to flow in the erlenmeyer flask through the frit for a 15 min duration after the aqueous foam M3 is deposited. The drainage liquid phase is then sampled, diluted once at 50% (so as to obtain a dilution rate similar to that of the standard-solutions), and then analysed by UV visible spectrometry (between 600 nm and 1 000 nm). The absorbance value corresponding to the copper signal is read out and then compared to the calibration straight line set beforehand.

[0161] After a 15 min duration, the residual concentration of cations Cu.sup.2+ is read out, in the drainage liquid phase, as being 1.29 g/L, which corresponds to 52% of the concentration of cations Cu.sup.2+ in solution S3 before injection. In other words, the aqueous foam M3 enabled 48% of cations Cu.sup.2+ to be retained.

[0162] By applying a similar protocol made from 100 mL of solution S4, in place of solution S3, a residual concentration of cations Cu.sup.2+ is obtained, in the drainage liquid phase, of 1.72 g/L, which corresponds to 69% of the concentration of cations Cu.sup.2+ in the solution S4 before injection. In other words, the aqueous foam M4 enabled 31% of cations Cu.sup.2+ to be retained.

Assessment of the Complexing Properties to Zn.SUP.2+ of Aqueous Foams M3 and M4

[0163] For assessing complexing properties of the aqueous foam M3 to Zn.sup.2+, a calibration stock-solution and working-solutions are made from solution S3.

[0164] For this, a similar protocol to that described above is reproduced for assessing the complexing properties to cations Cu.sup.2+.

[0165] A stock-solution comprising a 2.5 g/L initial concentration of cations Zn.sup.2+ is prepared by adding 1.042 g of ZnCl.sub.2 to the solution S3 diluted beforehand to 50% using deionised water. The working-solutions are then prepared according to a protocol similar to that previously described. These working-solutions are then re-diluted: deionised water is added in each working solution, until their respective volume is 10 times greater than their initial volume (this dilution enables the saturation of the UV-visible signal of zinc to be avoided).

[0166] The absorbance values corresponding to the zinc signal which are measured, by UV visible spectrometry on a wavelength range from 200 nm to 300 nm, for the different fractions of stock-solution and working-solutions, enabled a calibration straight line to be set.

[0167] 1.042 g of ZnCl.sub.2 have been added to 100 mL of solution S3, so as to obtain a solution with a 5 g/L initial concentration of cations Zn.sup.2+.

[0168] The protocol for producing the aqueous foam as described above has then been reproduced and the sampling of the drainage liquid phase flown 15 min after depositing the aqueous foam on the frit and collected in the erlenmeyer flask has been conducted.

[0169] A volume of this drainage liquid phase has been sampled and then diluted. For this, this volume has been multiplied by 20 by adding the suitable amount of deionised water. In this way, the drainage liquid phase undergoes the same dilution factor as the standard-solutions. The diluted drainage liquid phase is then analysed by UV visible spectrometry (between 200 nm and 3 000 nm). The absorbance value corresponding to the zinc signal has been read out and then compared to the calibration straight line set beforehand.

[0170] It is observed that, after a 15 min duration, the residual concentration of cations Zn.sup.2+, in the drainage liquid phase, is 1.40 g/L, which corresponds to 56% of the concentration of cations Zn.sup.2+ in solution S3 before injection. In other words, aqueous foam M3 enabled 44% of cations Zn.sup.2+ to be complexed.

[0171] By applying a similar protocol made from 100 mL of solution S4, in place of solution S3, a residual concentration of cations Zn.sup.2+, in the drainage liquid phase, of 1.49 g/L is obtained, which corresponds to 60% of the concentration of cations Zn.sup.2+ in solution S4 before injection. In other words, aqueous foam M4 enabled 40% of cations Zn.sup.2+ to be complexed.

Assessment of the Complexing Properties to Co.SUP.2+ of Aqueous Foams M3 and M4

[0172] For assessing the complexing properties of aqueous foam M3 to cations Co.sup.2+, a calibration stock-solution and working-solutions have been made from solution S3.

[0173] For this, a protocol similar to that described above for assessing the complexing properties to cations Cu.sup.2+ has been reproduced.

[0174] A stock-solution comprising an initial concentration of 2.5 g/L of cations Co.sup.2+ is prepared by adding 2.468 g of Co(NO.sub.3).sub.2,6H.sub.2O to the solution S3 diluted beforehand to 50% using deionised water. The working-solutions are then prepared according to a protocol similar to that previously described. These working-solutions are then re-diluted: deionised water is added in each working-solution, until their respective volume is 5 times greater than their initial volume (this dilution enables the saturation of the UV-visible signal of cobalt to be avoided).

[0175] The absorbance values corresponding to the cobalt signal measured by UV visible spectrometry on a wavelength range from 250 nm to 360 nm, for the different fractions of stock-solution and working-solutions, enabled a calibration straight line to be set.

[0176] 2.468 g of Co(NO.sub.3).sub.2,6H.sub.2O have been added to 100 mL of solution S3, so as to obtain a solution with a 5 g/L initial concentration of cations Co.sup.2+.

[0177] The protocol for producing the aqueous foam as described above has then been reproduced and the sampling of the drainage liquid phase flown 15 min after depositing the aqueous foam onto the frit and collected in the erlenmeyer flask has been conducted.

[0178] A volume of this drainage liquid phase has been sampled and then diluted. For this, this volume has been multiplied by 10 by adding the suitable amount of deionised water. In this way, the drainage liquid phase undergoes the same dilution factor as the standard-solutions. The diluted drainage liquid phase is then analysed by UV visible spectrometry (between 250 nm and 360 nm). The absorbance value corresponding to the cobalt signal has been read out and then compared to the calibration straight line set beforehand.

[0179] It is observed that, after a 15 min duration, the residual concentration of cations Co.sup.2+, in the drainage liquid phase, is 1.00 g/L, which corresponds to 40% of the concentration of cations Co.sup.2+ in solution S3 before injection. In other words, aqueous foam M3 enabled 60% of cations Co.sup.2+ to be complexed.

[0180] By applying a similar protocol made from 100 mL of solution S4, in place of solution S3, a residual concentration of cations Co.sup.2+ is obtained, in the drainage liquid phase, of 1.99 g/L, which corresponds to 80% of the concentration of cations Co.sup.2+ in solution S3 before injection. In other words, aqueous foam M4 only enabled 20% of cations Co.sup.2+ to be complexed.

[0181] The residual concentrations of cations Cu.sup.2+, Zn.sup.2+ and Co.sup.2+ in the drainage liquid phases from the different foams M3 and M4 are reported in FIG. 2.

[0182] This FIG. 2 clearly highlights that the aqueous foams M3 and M4 in accordance with the invention have complexing properties, since their residual concentrations are each lower than the initial concentrations.

[0183] FIG. 2 also shows that the complexing properties of an aqueous foam in accordance with the invention are improved by the presence of chitosan in the solution (solution S3) regardless of the cation considered.

[0184] The presence of chitosan improves particularly significantly the complexation, and thus retention or sequestration, of cations Co.sup.2+, which has an undeniable interest for any application for fighting against cobalt pollution, in particular the decontamination of cobalt 60 based ionising sources.

Assessment of the Self-Supporting Properties of Aqueous Foams

[0185] Two aqueous foams, noted M5 and C5, have been produced, M5 being an aqueous foam according to the invention and C5 being a comparative aqueous foam.

[0186] For assessing the self-supporting properties of each of these aqueous foams M5 and C5, the behaviour of an aggregate of each of them has been assessed after deposition on a surface in the absence of any support.

Production and Assessment of Aqueous Foam M5 (According to the Invention)

[0187] In a vessel containing 4 L water, 240 g of surfactant DP-SF/2 and 60 g of agar-agar are introduced. The solution obtained, noted S5, is then placed under stirring and heated at a 95 C. temperature until it is fully homogenous. The temperature is then thermally controlled at 58 C. until it is injected.

[0188] Solution S5 is then introduced in a compressed air foam generator marketed by the ERPI company. Contacting solution S5 with a pressurised gas, forming a two-phase mixture and injecting this two-phase mixture are concomitantly provided by diffusion of solution S5 as a spray through mesh wires on which a constant air flow is applied.

[0189] As a result, an aqueous foam M5, the expansion ratio ER of which can range from 5 to 80, is formed, depending on the flow rates of solution S5, on the one hand, and air, on the other hand.

[0190] It is observed that the films making up the alveolar structure of aqueous foam M5 gel upon cooling this aqueous foam M5.

[0191] Indeed, the gelling temperature depends on the agar-agar concentration in the solvent (here, water). But, in solution S5, this agar-agar concentration being 15 g/L solvent, the gelling temperature is in the order of 35 C.

[0192] Thus, at a temperature lower than the gelling temperature, and in particular at room temperature, the aqueous foam M5 that is obtained is sufficiently elastic to minimise its spreading during injection and thus enabling the formation of an aggregate, or a mound, of an aqueous foam M5 with a 70 cm height and a 2 m diameter, that is far beyond the required dimensions to consider that an aqueous foam is self-supporting in the absence of a support.

[0193] This aqueous foam M5 has the interest neither to collapse, near to drain, on a minimum period of 24 h, which facilitates handling and recovery after use thereof.

[0194] In the case of a use of an aqueous foam in accordance with the invention as a decontaminant, the non-draining properties of said aqueous foam are such that there will be neither streaming, nor infiltration of the aqueous phase of the aqueous foam into the sol, the aqueous foam being further possibly be easily recovered, for example by sucking or by means of a shovel.

Production and Assessment of (Comparative) Aqueous Foam C5

[0195] In a vessel containing 4 L water, 240 g of surfactant DP-SF/2 are introduced. The solution obtained, noted SC5, is then placed under stirring and at room temperature until it is fully homogenised.

[0196] Solution SC5 is then introduced in a foam generator marketed by the ERPI company. Contacting solution SC5 with a pressurised gas, forming the two-phase mixture and injecting this two-phase mixture are concomitantly provided by diffusing of solution SC5 as a spray through mesh wires on which a constant air flow is applied.

[0197] As previously described, an aqueous foam C5, the expansion ratio ER of which can range from 5 to 80, is formed, depending on the flow rates of solution SC5, on the one hand, and of air, on the other hand.

[0198] Unlike the previously described aqueous foam M5, which is characterised by excellent self-supporting and non-draining properties, this aqueous foam C5, which is produced from solution SC5 not comprising a gelling compound such as agar-agar, does not enable aggregates of aqueous foam which are self-supporting to be formed. Indeed, it has not been possible to make an aggregate, or a mound, with a 70 cm height and a 2 m diameter, which is stable on a period of 24 h, because of the spreading of the aggregate of aqueous foam C5 from the first hour following deposition. The streaming related to the drainage phenomenon also occurred within 5 min following deposition.

REFERENCE LIST

[0199] [1] U.S. Pat. No. 5,360,828 [0200] [2] U.S. Pat. No. 5,382,285