EP3077491A1

EP3077491A1 - Use of an oxidising alkaline gel to remove a biofilm on a surface of a solid substrate

Info

Publication number: EP3077491A1
Application number: EP14815271.3A
Authority: EP
Inventors: Amélie LUDWIG; Frédéric GOETTMANN; Fabien FRANCES; Romain CASTELLANI
Original assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2013-12-05
Filing date: 2014-12-03
Publication date: 2016-10-12
Anticipated expiration: 2034-12-03
Also published as: FR3014336B1; FR3014336A1; US20160298060A1; EP3077491B1; WO2015082548A1; ES2718376T3; US9834744B2

Abstract

The invention relates to the use of a gel, consisting of a colloidal solution including, preferably consisting of: 5 wt % to 30 wt %, preferably 5 wt % to 25 wt %, preferably still 8 wt % to 20 wt % relative to the weight of the gel, of at least one inorganic thickening agent; a mineral base selected among the alkaline metal hydroxides, the alkaline-earth metal hydroxides, and the mixtures thereof, said mineral base being present in an amount of 0.05 to 10 mol/L of gel, preferably in an amount of 0.1 to 5 mol/L of gel; a stable oxidising agent in a basic medium selected among the permanganates, the persulfates, ozone, the hypochlorites, and the mixtures thereof, said stable oxidising agent in a basic medium being present in an amount of 0.05 to 5 mol/L of gel, preferably 0.1 to 2 mol/L of gel; 0.1 wt % to 2 wt % relative to the weight of the gel of at least one surfactant; and a solvent; the gel not containing a superabsorbent polymer; in order to remove a biofilm located on a surface of a solid substrate.

Description

USE OF AN ALKALINE OXIDIZING GEL TO REMOVE A BIOFILM ON A

SURFACE OF A SOLID SUBSTRATE.

DESCRIPTION TECHNICAL FIELD

The present invention relates to the use of an oxidizing alkaline gel for removing a biofilm from a surface of a solid substrate.

The technical field of the invention can be defined as that of the treatment of polluted surfaces, soiled, deteriorated by biofilms, in order to eliminate these biofilms from these surfaces and in particular to improve the visual appearance of these surfaces.

The invention can be applied to all kinds of surfaces such as organic polymer surfaces, for example plastics; surfaces made of vitreous materials; surfaces made of cementitious materials such as cements, pastes, mortars and concretes; surfaces of raw or cooked earth; brick or tile surfaces; plaster surfaces; ceramic surfaces; natural or artificial stone surfaces; plaster surfaces; fiberglass surfaces; fiber cement surfaces; asphalt or tar surfaces; metal or metal alloy surfaces, for example steel, galvanized steel or zinc; and surfaces made of cellulose-based materials such as wood. These surfaces can be painted or not.

The invention applies in particular to the elimination of biofilms on outdoor surfaces, located outdoors, buildings, constructions, and objects or structures.

But the invention can also be applied to the removal of biofilms from surfaces of aquatic vehicles such as boats; land vehicles such as cars, trucks or motorcycles; aircraft such as airplanes, helicopters, seaplanes, or drones; various domestic materials and equipment such as furniture; apparatus and industrial devices, such as pipes, in particular apparatus and devices which are in very humid environments or in which cold spots are created; and agri-food products including compact agri-food products; or else medical devices or apparatus. It should be noted that there is no limitation as to the area on which the biofilms removed according to the invention can be found. Indeed, if in temperate climates the surfaces on which biofilms can develop are relatively limited, it is not the same in tropical humid climates where biofilms are likely to affect almost all surfaces.

STATE OF THE PRIOR ART

Construction materials outside, that is to say outdoors, such as stones, bricks, plaster, tiles, are continuously exposed to different atmospheric agents that can damage them, such as wind, rain, sun, or humidity.

To the action of these atmospheric agents is added the effect of biological agents such as microorganisms, which are capable of developing on any surface in the form of biofilms.

With the industrial era, the concentration of organic and inorganic compounds in the air has greatly increased, aggravating the formation process of these biofilms that combine the double disadvantage of being unsightly because they are mostly black, red or green and lead to accelerated deterioration of building materials, known as biodeterioration.

The term biofilm is commonly used in this field of the art and has a widely recognized and accepted meaning.

Biofilms can be defined as clean ecosystems consisting essentially of associations of algae, fungi, bacteria and cyanobacteria, all immersed in a gel or matrix of exopolymers that protects them from external aggressions and makes them very resistant (see document [1]).

The elimination of biofilms is thus much more difficult than the elimination of simple microorganisms, because in biofilms, microorganisms are structurally surrounded and protected by exopolymers.

A definition of biofilms is also provided in US-A1-2012 / 0232153 [2] in paragraph [0019], to which reference may be made. The interior of buildings is also free of problems related to the development of biofilms. Wetlands in particular, such as bathrooms, water features, cold spots in bedrooms, constitute a privileged ground for the appearance of black spots that are biofilms (see the book «Biofilm when microbes get organized "by R. Briandet, L. Fechner, M. Naïali and C. Dreano, Editions Quae 2012 [3]). Besides, once again, an obvious aesthetic problem, these biofilms can pose human health problems, related to allergies that they are likely to cause in some people.

To eliminate biofilms and the tasks related to the formation of these biofilms many techniques of cleaning, washing, exist and are used today.

Table 1 below provides a non-exhaustive list of these techniques, with their main advantages and disadvantages.

Application Technique Advantages Disadvantages Reference cleaning

Exterior High Pressure Jet - High Efficiency - Risks of K. Ammerman,

- Possibility of degradation of "Algae, the treatment of materials (abrasion) growing large areas - Risks of projections problem",

- Non polluting. and Dirt on Interface, January from other parts of the 2007, pages 37 to 42 building [4].

- No protective effect.

Steam cleaning Indoor - Non polluting. - Difficulty to eliminate

all the coloring

- Risks

damage

coatings.

Washing by Interior / - Non polluting (in - Limited efficiency.

surface-outdoor solutions)

active - Ease of use.

Inner Wash / - High Efficiency - Toxic Compound for K. Ammerman, Outdoor Water Solutions - Combines One Plant "Algae, the

Javel action - Burning risk growing

disinfectant and chemical problem, whitening. - Interface rinsing effluents, January eliminated in 2007, pages 37 to rainwater circuits. 42 [4].

Washing by Interior / - High efficiency - Risk of burn K. Ammerman, Outdoor solutions - Combines a chemical "Algae, the peroxides (e.g. water action - riddles rinsing growing oxygenated) disinfectant and eliminated in the problems",

bleaching rainwater circuits. Interface, January - No toxicity 2007, pages 37 to residual. 42 [4].

Washing by Interior / - Efficiency - Toxic compound for K. Ammerman, basic solutions Exterior medium (not the plants (with strong 'Algae, the

action doses) growing whitening). - Risk of burn problem,

Chemical Interface, January

- Rinsing effluents 2007, pages 37 to eliminated in the 42 [4].

rainwater circuits.

Interior Wash / - High Efficiency - Potential Cost G. G. Griese et al. Outdoor solutions - Combines a high "Acidic biofilm hydroalcoholic action - Effluent rinses remediation" US - disinfectant and disposed of in Al-2012/0232153 detergent. rainwater circuits. [2]

Formulated Gels Exterior - High Efficiency - Potential Costs K. Ammerman, (Fungicides + - Assure a High 'Algae, the polymers') Protection in - Leaching from the growing

the weather. fungicide in the problems, "rainwater. Interface, January

2007, pages 37 to 42 [4].

Table 1: List of cleaning techniques most commonly used to eliminate tasks related to biofilm formation.

As can be seen in Table 1, most of the proposed techniques are satisfactorily effective. However, all have a number of disadvantages, mainly due to the fact that they pose risks to the support to be treated and / or the manipulator and / or the environment.

Furthermore, in the context of nuclear decontamination, gelled formulations that make it possible to overcome the problems related to the pulverulent character of the dry waste, and to increase the efficiency of the process using a gel have been the subject of documents [5] and [6].

These documents describe inorganic colloidal gels called "aspirable gels", specifically formulated to be sprayed, then to dry by fracturing, while trapping and confining the radioactive contamination in the form of non-pulverulent flakes, aspirable, and directly packable and storable.

Document [5] describes a gel consisting of a colloidal solution comprising an inorganic viscosifying agent, generally silica or alumina, an active agent treatment which is for example an acid or an inorganic base such as sodium hydroxide or potassium hydroxide, and optionally an oxidizing agent having a normal redox potential Eo greater than 1.4 V in a strong acid medium such as Ce (IV), Co (III), or Ag (II).

Document [6] describes a gel consisting of a colloidal solution comprising an inorganic viscosifying agent, generally silica or alumina, a surfactant, an acid or an inorganic base, optionally an oxidizing agent having a normal potential. oxidation-reduction Eo greater than 1.4 V in strong acid medium such as Ce (IV), Co (III), or Ag (M).

These inorganic colloidal gels, because of the different constituents used in their composition have a rheology that allows their spraying on a contaminated surface, then their adhesion to this surface, even vertical, without sinking.

This thus allows prolonged contact between the contaminant and the active decontamination agent, without the mechanical properties of the substrate being altered.

Following its spraying, the gel dries, fractures, and produces dry residues, called "flakes", adhering to the substrate and which are subsequently removed by brushing or aspiration to be directly conditioned.

The decontamination processes that use these suction gels are therefore dry decontamination processes, generating no liquid effluent and few dry solid residues. Indeed, these dry solid residues represent on average only a quarter of the initially sprayed gel mass. In addition, these methods limit the time of exposure of operators to radioactive contamination, because of their easy implementation by spraying and suctioning of dry residues, and the fact that the presence of the operator is not required during the drying of the gel.

The gels described in documents [5] and [6], however, are specifically intended for the radioactive decontamination of surfaces, particularly in the context of the dismantling of nuclear installations, and are in no way adapted to the removal of surface biofilms. or even capable of being adapted to solve the extremely specific problem of removing surface biofilms. The documents FR-A1-2962046 and WO-A1-2012 / 001046 [7] relate to an "aspirable" biological decontamination gel and a process for the biological decontamination of surfaces using this gel.

This gel consists of a colloidal solution comprising at least one inorganic viscosifying agent, at least one biological decontamination agent, at least one superabsorbent polymer, and at least one surfactant.

The superabsorbent polymer, such as sodium polyacrylate, makes it possible to improve the gel efficiency on porous materials, for example mortars.

The gel of the document [7] is, however, specifically intended for the biological decontamination of surfaces, in particular for the so-called post-venal decontamination of surfaces.

There is no mention or suggestion in document [7] that the freezing of this document could solve the extremely specific problem of the elimination of surface biofilms, which is a totally different problem from the problem of biological decontamination - especially post eventementielle- because of the very particular and very complex nature of biofilms.

Indeed, the biological decontamination of a surface consists simply of eliminating biological species, essentially biotoxic, isolated, dispersed, exposed unprotected on this surface, whereas biofilms are complex systems in which populations of microorganisms are surrounded. and protected by polysaccharides and other macromolecules commonly called exopolysaccharides. The problems posed by the elimination of biofilms are therefore totally different and certainly more complex and more difficult than those encountered in the simple decontamination of a surface contaminated only by isolated biological species. The fact that a gel has been used successfully for the biological decontamination of a surface does not mean that the same gel may be suitable for the removal of biofilms in which the microorganisms are protected by an exopolysaccharide gel. which must first be destroyed. In addition, a biofilm includes, in addition, many other components contributing in particular to its coloring little aesthetic, for example red or black, which must also be removed to give the surface its original appearance free of soiling.

In addition, it has been demonstrated that the gel of the document [7] has a very short shelf life, for example of a few weeks.

In view of the foregoing, therefore, there is a need for a technique for removing biofilms from the surface of substrates which, while having a high efficiency, and at least as high as that of the techniques listed in Table 1, do not not present the disadvantages, defects and disadvantages of these techniques.

The object of the present invention is to meet, among others, this need.

STATEMENT OF THE INVENTION

Surprisingly, it has been demonstrated according to the invention that the use of a gel having a specific composition makes it possible to achieve the above purpose and to eliminate biofilms.

The subject of the invention is therefore the use of a gel constituted by a colloidal solution comprising, preferably consisting of:

5% to 30% by weight, preferably 5% to 25% by weight, more preferably 8% to 20% by weight, based on the weight of the gel, of at least one inorganic viscosifying agent;

a mineral base selected from alkali metal hydroxides, alkaline earth metal hydroxides, and mixtures thereof, said inorganic base being present at a level of from 0.05 to 10 mol / L of gel, preferably from 0.1 to 5 mol / L of gel;

a stable oxidizing agent in a basic medium chosen from permanganates, persulfates, ozone, hypochlorites, and mixtures thereof, the said basic stable oxidizing agent being present in a proportion of 0.05 to 5 mol / l of gel, preferably from 0.1 to 2 mol / L of gel;

0.1% to 2% by weight, based on the weight of the gel, of at least one surfactant;

and a solvent; and the gel not containing superabsorbent polymer;

to remove a biofilm on a surface of a solid substrate.

It can generally be considered that the colloidal solution comprises "the rest of solvent".

"Solvent residue" means that the solvent is always present in the colloidal solution and that the amount of solvent is such that, when it is added to the quantities of the components of the colloidal solution other than the solvent (that these components are mandatory or optional components mentioned above, or other additional optional components mentioned or not mentioned), the total amount of all the components of the colloidal solution is 100% by weight.

The use of the specific gel described above to remove a biofilm from a surface of a solid substrate has never been described in the prior art.

The gel used according to the invention, according to a first fundamental characteristic, is defined first of all by the fact that it contains the combination of a specific mineral base chosen from alkali metal hydroxides, alkaline earth metal hydroxides, and their mixtures, a specific biocidal oxidizing agent which is a stable oxidizing agent in a basic medium selected from permanganates, persulfates, ozone, hypochlorites, and mixtures thereof, and a surfactant.

The gel used according to the invention is a basic gel, that is to say one whose pH is generally greater than 7, preferably 12 to 14, and by basic medium is meant a medium whose pH is generally greater than at 7, preferably from 12 to 14.

The gel used according to the invention is then defined in that it does not contain a superabsorbent polymer.

It can be said that the combination of a specific mineral base such as an alkaline hydroxide, such as sodium hydroxide, or an alkaline earth metal hydroxide; a specific oxidizing agent such as hypochlorite, such as sodium hypochlorite which has a biocidal activity; and finally a surfactant is a true synergistic combination, as explained below. Indeed, the gel used according to the invention has a high efficiency in the context of the elimination of biofilms which is due to the combination of the decontaminating action, biocide, and bleaching of the oxidizing agent such as bleach, and the degreasing action of the mineral base, such as sodium hydroxide, and the surfactant.

It is this combination of effects due to the oxidizing agent, the base, and the surfactant that makes the gel extremely effective during the removal of biofilms.

In addition, the specific oxidizing agent, such as bleach, is not only a simple oxidizing species, it is also an excellent biocide, in other words, in addition to its degreasing action, the mineral base such as soda therefore also has a biocidal action.

The gel used according to the invention which contains the combination of a specific mineral base such as an alkali metal hydroxide, such as sodium hydroxide, or an alkaline earth metal hydroxide, and a specific oxidizing agent such as hypochlorite, as sodium hypochlorite, a biocidal activity enhanced especially with respect to gels, such as those of document [7] containing only a mineral base such as sodium hydroxide.

It can be considered that the gel used according to the invention comprises two biocidal compounds, namely a first biocidal active compound which is a mineral base such as sodium hydroxide and a second biocidal active compound which is an oxidizing agent such as bleach.

It is the combination of these two compounds that makes the gel even more effective against biofilm biological species, while the degreasing, oxidizing and whitening properties of the gel also ensure complete elimination, destruction the components of the biofilm. In particular, the unsightly, "dirty" color imparted on the surface by the biofilm is removed by the gel used according to the invention, and the treated surface returns to its original "clean" color which it possessed before the biofilm is formed. .

Even more surprisingly, the gel used according to the invention which thus has a high efficiency for eliminating biofilms, is however also stable, and has an increased stability over time. Indeed, the inventors have demonstrated that the poor stability over time of the biological decontamination gel of the document [7] was due to the superabsorbent polymer because this superabsorbent polymer modifies the rheology of the gel during its storage, which makes it makes it unsuitable for spraying and application on a vertical surface due to poor adhesion.

The inventors have furthermore demonstrated that the use of oxidizing agents in the presence of superabsorbent polymers considerably reduces the stability over time of the biological decontamination gel of the document [7], to a shorter duration. to a few days.

The absence of superabsorbent polymer in the gel which is used according to the invention thus greatly improves the stability over time.

It is quite unexpected and surprising that, according to the invention, the gel described above can be used to remove a biofilm on solid surfaces and ensures the elimination of these biofilms with high efficiency due to the synergistic combination of actions and effects of each of its constituents. According to the invention, at the end of the use of the gel, a cleaned surface is obtained, freed of the biofilm, without soiling, unsightly colorings and whose appearance is close to its initial appearance before formation of the biofilm.

The effectiveness of the use according to the invention is demonstrated by Examples 2, 3 and the figures illustrating these examples.

Preferably, the mineral base is chosen from sodium hydroxide, potassium hydroxide, and mixtures thereof, and the stable oxidizing agent in basic medium is chosen from hypochlorites, and mixtures thereof.

A particularly preferred gel contains a combination of sodium hydroxide and sodium hypochlorite.

In this case, the sodium hydroxide is present in a proportion of 0.05 to 10 mol / l of gel, preferably 0.5 to 5 mol / l of gel, and the sodium hypochlorite is present in a proportion of 0.05 to 5 mol / L of gel, preferably from 0.1 to 1.5 mol / L of gel.

Indeed, the addition of sodium hypochlorite (bleach concentrate) makes it possible to reinforce the biocidal aggressiveness of the gel used compared with a gel containing only the soda, without fundamentally modifying the physicochemical properties or the rheology.

Soda is also a good biocide. In addition it is an excellent stabilizer for sodium hypochlorite, and it guarantees a good preservation of the hypochlorite ion content while ensuring a biocidal function.

In summary, the use according to the invention makes it possible to meet all the needs mentioned above.

The use according to the invention provides a solution to the problems presented by known biofilm removal techniques, such as those shown in Table 1, without the disadvantages.

The use according to the invention does not in particular run any risk to the substrate, substrate to be treated and / or the manipulator and / or the environment.

The gel used according to the invention is a colloidal solution, which means that the gel used according to the invention contains inorganic solid particles, mineral, viscosity agent whose elementary particles, primary, have a size generally from 2 to 200 nm.

Due to the use of a generally exclusively inorganic viscosifying agent, without an organic viscosity agent, the organic matter content of the gel used according to the invention is generally less than 4% by weight, preferably less than 2% by weight. , which constitutes yet another advantage of the gels used according to the invention.

These inorganic, solid inorganic particles act as a viscosity agent to allow the solution, for example the aqueous solution, to gel and thus adhere to the surfaces to be treated, whatever their geometry, their shape, their size, and wherever biofilms are to be removed.

Advantageously, the inorganic viscosifying agent may be chosen from metal oxides such as aluminas, metalloid oxides with the exception of silica, metal hydroxides, metalloid hydroxides, metal oxyhydroxides, oxyhydroxides of metalloids, aluminosilicates, clays such as smectite, and mixtures thereof; these viscosifying agents are stable in basic medium. In particular, the inorganic viscosifying agent may be chosen from aluminas

The inorganic viscosifying agent may comprise only one alumina or a mixture thereof, namely a mixture of two different or more aluminas (mixture

The alumina may be chosen from calcined aluminas, crushed calcined aluminas, and mixtures thereof.

By way of example, mention may be made of the product sold by EVONIK INDUSTRIES under the trade name "Aeroxide Alu C" which is fine-pyrogenic alumina and which has a BET specific surface area of 100 m ² / g.

Advantageously, according to the invention, the inorganic viscosifying agent consists of one or more alumina (s). This or these alumina (s) represent (s) generally from 5% to 30% by weight relative to the mass of the gel.

In this case, the alumina (s) is (are) preferably at a concentration of 8% to 17% by weight relative to the total mass of the gel (to ensure drying of the gel at a temperature of between 20 ° C. C and 50 ° C and at a relative humidity of between 20% and 60% on average in 30 minutes to 5 hours).

The nature of the mineral viscosifying agent, especially when it consists of one or more alumina (s), unexpectedly influences the drying of the gel used according to the invention and the particle size of the residue obtained.

Indeed, the dry gel is in the form of particles of controlled size, more precisely millimetric solid flakes, the size of which generally ranges from 1 to 10 mm, preferably from 2 to 5 mm, in particular thanks to the abovementioned compositions, in particular when the viscosing agent consists of one or more alumina (s).

Note that the size of the particles generally corresponds to their largest dimension.

The gel used according to the invention contains a specific mineral base and a specific oxidizing active agent as defined above.

This base and this specific oxidizing agent may in particular be described as biocidal agents. By biocidal agent is meant an agent which when in contact with a biological species contained in a biofilm inactivates or kills it.

By biological species, we mean any type of microorganism that can be found in a biofilm such as bacteria, fungi, yeasts, viruses, toxins, spores and protozoa.

The base and the oxidizing agent are used at the concentrations mentioned above, in order to guarantee a biofilm elimination capacity compatible with the gel drying time, and to ensure, for example, a drying of the gel at a temperature of between 20 ° C. C and 50 ° C and at a relative humidity of between 20% and 60% on average in 30 minutes to 5 hours.

It should be noted again that the gel used according to the invention being a basic gel, it has, besides the biocidal and whitening action, a degreasing action. The surfactant also contributes to this degreasing action.

In order to achieve a total efficiency, including in the most unfavorable climatic conditions with respect to the drying time of the gel, the gel used according to the invention can have a broad concentration range of mineral base (s) ( s).

Indeed, the increase in the concentration of mineral base such as NaOH or KOH, acting in particular as a biocidal agent, makes it possible to considerably increase the elimination rates of the biofilm.

The mineral base is used at the concentration defined above to ensure drying of the gel at a temperature between 20 ° C and 50 ° C and relative humidity of between 20% and 60% on average in 30 minutes to 5 hours.

In the case of the treatment of a cement matrix, the basic pH of the gel, which is induced for example by the use of sodium hydroxide or potassium hydroxide, makes it possible to avoid acid-base reactions between the material to be decontaminated and the gel, which affect the integrity of the material but also that of the gel on the surface and therefore the efficiency of the process.

The hygroscopic nature of sodium hydroxide or potassium hydroxide is also a considerable asset in slowing down the phenomenon of gel drying. The contact time between the gel and the biofilm is then considerably increased.

Indeed, the competition between the evaporation process of the aqueous phase and the water recovery of the sodium hydroxide or potassium hydroxide crystals favorably modifies the drying kinetics of the gel.

The gel used according to the invention does not contain, unlike the gel described in document [7], superabsorbent polymer, in other words, the gel used according to the invention is free of superabsorbent polymer.

By "superabsorbent polymer" also referred to as "SAP" is generally meant a polymer capable, in the dry state, of spontaneously absorbing at least 10 times, preferably at least 20 times its weight of aqueous liquid, particularly water and especially distilled water. Such superabsorbent polymers have been described in detail in document [7] already cited.

The gel used according to the invention contains a surfactant, or a mixture of surfactants, preferably chosen from nonionic surfactants, such as block copolymers, which are sequenced, for example block copolymers. ethylene oxide and propylene oxide, and the ethoxylated fatty acids; and their mixtures.

For this type of gel, the surfactants are preferably block copolymers sold by BASF under the name "Pluronic ^* ". For example, Pluronic ^® PE6200 can be used.

Pluronics ^* are block copolymers of ethylene oxide and propylene oxide.

As indicated above, just like the base, the surfactant (s) have a degreasing action which contributes to the elimination of the biofilm.

These surfactants also influence the rheological properties of the gel, including the thixotropic character of the product and the recovery time, in order to make it sprayable on floors, walls or ceilings, avoiding the appearance of sagging.

The surfactants also make it possible to control the adhesion of the dry waste and to control the size of the flakes of dry residue in order to guarantee the non-dustiness of the waste. These surfactants finally control the phenomenon of bleeding of the gel over time and thus improve its ability to be sprayed after storage.

The solvent according to the invention is generally selected from water, organic solvents, and mixtures thereof.

A preferred solvent is water, and in this case the solvent is therefore water, comprises 100% water.

Advantageously, the gel used according to the invention may, in addition, comprise one or more inorganic pigment (s) such as iron oxide.

Generally, in the use according to the invention is carried out at least one cycle comprising the following successive steps:

a) the gel is applied as described above on said surface; b) the gel is maintained on the surface for at least sufficient time for the gel to destroy the biofilm, and for the gel to dry and form a dry, solid, non-powdery residue containing compounds resulting from the destruction of the biofilm;

c) removing the dry and solid non-pulverulent residue containing the compounds resulting from the destruction of the biofilm.

Generally, the solid residue does not contain living biological species and the compounds resulting from the destruction of the biofilm do not include living biological species.

The biological species initially present in the biofilm are killed, destroyed by the action of the gel and the biological species destroyed, "killed", "dead", which are therefore part of the compounds resulting from the destruction of the biofilm, are recovered in the residue. dry and solid, ie usually in dry gel flakes.

Advantageously, the substrate is in at least one material selected from metals and alloys such as stainless steel, galvanized steel, or zinc; painted steels; organic polymers such as plastics or rubbers such as polyvinyl chloride or PVC, polypropylenes or PPs, polyethylenes or PEs, in particular high density polyethylenes or HDPEs, poly (methyl methacrylates) or PMMA, polyvinylidene fluoride or PVDF, polycarbonates or PCs; the glasses ; cementitious materials such as pastes, cements, mortars and concretes; plasters; the bricks ; tiles ; raw or cooked earth; natural or artificial stones; coatings; fiberglass; fibrocement; asphalt; tar ; slate; cellulose-based materials such as wood; and ceramics.

The substrate can be painted or not.

Advantageously, the gel is applied to the surface of the solid substrate on which the biofilm is located at a rate of 100 g to 2000 g of gel per m ² of surface, preferably of 500 to 1500 g of gel per m ² of surface, of more preferably from 600 to 1000 g per m ² of surface, which generally corresponds to a thickness of gel deposited on the surface of between 0.5 mm and 2 mm.

Advantageously, the gel is applied to the surface of the solid substrate by spraying, with a brush, or with a trowel.

Advantageously (during step b)), the drying is carried out at a temperature of 1 ° C. to 50 ° C., preferably of 15 ° C. to 25 ° C., and at a relative humidity of 20% to 80%. preferably from 20% to 70%.

Advantageously, the gel is maintained on the surface for a period of 2 to 72 hours, preferably 2 to 48 hours, more preferably 3 to 24 hours.

Advantageously, the dry and solid residue is in the form of particles, for example flakes, of a size of 1 to 10 mm, preferably 2 to 5 mm.

Advantageously, the dry and solid residue is removed from the surface of the solid substrate by brushing and / or suctioning.

Advantageously, the cycle described above can be repeated for example from 1 to 10 times using the same gel during all the cycles or by using different gels during one or more cycle (s).

Advantageously, during step b), the gel, before total drying, is rewetted with a solution of mineral base and oxidizing agent, preferably with the mineral base solution and oxidizing agent applied during the step a) in the solvent of this gel.

In other words, during step b), the gel can, before total drying, be rewetted with the mineral base solution and oxidizing agent contained in the gel already described above, which then generally avoids repeating the application of the gel on the surface and causes a reagent economy and a limited amount of waste. This rewetting operation can be repeated.

In summary, the use of the gel according to the invention has among others the following advantageous properties:

- The gel is an inorganic gel that avoids the risk of projection and coloring of the surface;

high efficiency linked to the combination of the following effects:

o Decontaminant and whitening action of the oxidant

o degreasing action of the base and surfactants - a great ease of implementation for example by brush, individual spray or spray gun,

adhesion to the walls,

the dry treatment of a very wide range of materials, the absence of mechanical or physical alteration of the materials at the end of the treatment, in particular the gel used, is totally harmless to most building materials because of its basic character,

implementing the process under varying climatic conditions, reducing the volume of waste,

the ease of recovery of dry waste,

- pollution risks limited by the formation of flakes that can be easily collected for example by suction or brushing and therefore do not enter the rainwater drainage networks,

the low exposure of operators to biological species contained in the biofilm and residues.

It is finally noted that the use according to the invention does, unlike the techniques described above (Table 1), run no risk to the substrate, substrate to be treated and / or the manipulator and / or the environment. Other features and advantages of the invention will appear better on reading the detailed description which follows, this description being given for illustrative and non-limiting, in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (A, B, C) presents photographs which show the appearance of the surface of the wall treated according to the invention, during the different stages of the test carried out in example 2, namely: initial state of the wall surface (A); the appearance of the wall surface after application of the brush gel on part of the wall surface (B); the appearance of the wall surface after drying for 48 hours and removal of dry gel flakes by gentle brushing (C).

Fig. 2B is a graph showing the results of an analysis of the gray values performed on the gray-scale converted Figure 1C image along the line shown in Fig. 2A (similar to Fig. 1C) .

In FIG. 2B, on the abscissa, the distance (in pixels) is plotted, and in the ordinate the value of gray is plotted.

FIG. 3 (A, B, C, D) shows photographs which show the appearance of the surface of the guardrail treated according to the invention, during the different stages of the test carried out in example 3, namely : the initial state of the surface of the railing (A); the appearance of the surface of the railing after application of the gel with a brush on a part of the surface of the railing (B); the appearance of the surface of the railing after drying for 48 hours of the gel applied on a part of the surface of the railing (C); the appearance of the surface of the railing after removal of dry gel flakes by gentle brushing (D).

FIG. 4 shows the two surface areas of the railing (a first zone 41 being situated in the part of the surface treated by the gel and a second zone 42 being located in the part of the surface not treated with the gel) in An average gray level was calculated on the image of the 3D Figure converted into gray levels. DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

The gel used according to the invention can be easily prepared at room temperature.

For example, the gel used according to the invention may be prepared by gradually adding, the inorganic viscosity agent (s), for example the alumina (s) and / or the one or more silica (s), to a solution containing the combination of an inorganic base and an oxidizing agent, the surfactant (s), and any pigment (s). This solution may be prepared for example by first preparing a solution of the oxidizing agent, for example a sodium hypochlorite solution in demineralized water, and then mixing with this oxidizing agent solution, the base mineral, the surfactant (s), and any pigment (s). This mixture can be produced by mechanical stirring, for example by means of a mechanical stirrer equipped with a three blade propeller. The rotational speed is for example 200 rpm, and the duration of the stirring is for example 3 to 5 minutes.

The addition of the inorganic viscosity agent (s) to the solution containing the mixture of an inorganic base and an oxidizing agent, the surfactant (s), and the Any pigment (s) can be made by simply pouring the viscosity agent (s) into said solution. When adding the inorganic viscosity agent (s), the solution containing the mixture of an inorganic base and an oxidizing agent, the surfactant (s), and the or the pigment (s), if any, is generally kept under mechanical stirring.

This agitation can be, for example, carried out by means of a mechanical stirrer equipped with a three blade propeller.

The stirring speed is generally increased gradually as the viscosity of the solution increases, finally reaching a stirring speed of, for example, between 400 and 600 rpm, without there being projections. After the end of the addition of the mineral viscosity (s) (s), the stirring is continued, for example for 2 to 5 minutes, so as to obtain a perfectly homogeneous gel.

It is obvious that other gel preparation protocols used according to the invention can be implemented with an addition of the gel components in a different order from that mentioned above.

Generally, the gel used according to the invention must have a viscosity of less than 200 mPa.s under a shear of 1000 s ¹ so as to allow spraying on the surface to be decontaminated remotely (for example at a distance of 1 to 5 m) or close (for example at a distance less than 1 m, preferably from 50 to 80 cm). The recovery time of the viscosity should generally be less than one second and the viscosity under low shear greater than 10 Pa s not to sink on the wall.

It should be noted that the surfactant of the gel used according to the invention favorably and significantly influences the rheological properties of the gel used according to the invention. This surfactant allows in particular that the gel used according to the invention can be implemented by spraying and avoids the risks of spreading or sagging during the treatment of vertical surfaces and ceilings. This surfactant also makes it possible to limit the phenomenon of bleeding observed during the conservation of the gel.

The gel thus prepared is then applied to the solid surface to be cleaned of a substrate made of a solid material.

Solid surface to be cleaned means a solid surface on which is a biofilm that is desired to eliminate.

Except for aluminum alloy light alloys, there is no limitation on the material that constitutes the surface to be cleaned, in fact the gel used makes it possible to treat all kinds of fragile materials without any damage.

The gel used according to the invention does not generate any alteration, erosion, attack, chemical, mechanical or physical of the treated material. The gel used according to the invention is therefore in no way detrimental to the integrity of the treated materials and even allows their reuse. Thus, sensitive materials such as military equipment are preserved and may after their cleaning be reused, while monuments, buildings, works of art such as sculptures, treated with the gel according to the invention are absolutely not degraded and have their visual and structural integrity preserved.

This material of the substrate may therefore be chosen from, for example, metals or alloys such as stainless steel, polymers such as plastics or rubbers, among which mention may be made of PVC, PP, PE, in particular HDPE, PMMA, PVDF, PC, glasses, cements, mortars and concretes, plaster, bricks, natural or artificial stone, plaster, ceramics.

In all cases (see Examples 2 and 3 and Figures), whatever the material, for example coating or cement, the cleaning efficiency according to the invention is total.

The treated surface can be painted or unpainted.

There is also no limitation as to the shape, geometry and size of the surface to be cleaned, the gel used according to the invention allows the treatment of large surfaces, complex geometries, having for example hollow, angles nooks.

The gel used according to the invention ensures the efficient treatment not only of horizontal surfaces such as balcony floors or railings or window sills, but also of vertical surfaces such as walls, facades, or inclined or overhanging surfaces such as only ceilings.

Compared to existing techniques that implement liquids such as solutions, the invention uses a gel, which is particularly advantageous for the treatment of large surface materials, non-transportable and implanted outside. Indeed, the method according to the invention because of the implementation of a gel, allows cleaning in situ by avoiding the spread of chemical solutions in the environment and the dispersion of contaminating species.

The gel according to the invention can be applied to the surface to be treated by all the application methods known to those skilled in the art.

Conventional methods are spraying, for example by spraying, or applying by means of a brush, or a trowel.

For the spray application of the gel on the surface to be treated, the colloidal solution may for example be conveyed via a low pressure pump, for example a pump that implements a pressure less than or equal to 7 bar, or about 7.10 ⁵ Pascals.

The burst of the gel jet on the surface can be obtained for example by means of a jet nozzle or round jet.

The distance between the pump and the nozzle may be arbitrary, for example it may be from 1 to 50 m, in particular from 1 to 25 m.

The sufficiently short viscosity recovery time of the gels used according to the invention allows the spray gels to adhere to all surfaces, for example to walls.

The amount of gel deposited on the surface to be treated is generally from 100 to

2000 g / m ² , preferably from 500 to 1500 g / m ² , more preferably from 600 to 1000 g / m ² .

The amount of gel deposited per unit area and, consequently, the thickness of the deposited gel influences the rate of drying.

Thus, when spraying a film, layer of gel with a thickness of 0.5 mm to 2 mm on the surface to be treated, the effective contact time between the gel and the materials is then equivalent to its drying time , during which time the active ingredient contained in the gel will interact with the biofilm.

In addition, it has been surprisingly shown that the amount of gel deposited when it is in the ranges mentioned above and in particular when it is greater than 500 g / m ² and in particular in the range of 500 to 1500 g / m ² , which corresponds to a minimum thickness of deposited gel for example greater than 500 μιη for a deposited gel quantity greater than 500 g / m ² , allowed after drying of the gel to obtain fracturing of the gel in the form millimetric flakes, for example of a size of 1 to 10 mm, preferably 2 to 5 mm aspirable.

The quantity of gel deposited and therefore the deposited gel thickness, preferably greater than 500 g / m ^2, ie 500 μιη, is the fundamental parameter which influences the size of the dry residues formed after drying of the gel and which thus ensures that residues Millimeter sized and not powdery residues are formed, such residues being easily removed by a mechanical process and preferably by suction. However, it should also be noted that, thanks to the low concentration surfactant, the gel drying is improved and leads to a homogeneous fracturing phenomenon with a size of the mono-dispersed dry residues and an increased ability of the dry residues to detach from the support.

The gel is then held on the surface to be treated for the duration necessary for drying. During this drying step, which can be considered as constituting the active phase of the process according to the invention, the solvent contained in the gel, namely generally the water contained in the gel evaporates to the obtaining a dry and solid residue.

The drying time depends on the composition of the gel in the concentration ranges of its constituents given above, but also, as already mentioned, on the amount of gel deposited per unit area, that is to say the deposited gel thickness.

The drying time also depends on the climatic conditions, namely the temperature, the ventilation and the relative humidity of the atmosphere in which the solid surface is located.

The process according to the invention can be carried out under extremely wide climatic conditions, namely at a temperature T of 1 ° C. to 50 ° C. and at a relative humidity RH of 20% to 80%.

The drying time of the gel according to the invention is therefore generally from 1 hour to 24 hours at a temperature T of 1 ° C. to 50 ° C. and at a relative humidity RH of 20% to 80%.

It should be noted that the formulation of the gel used according to the invention especially when it contains surfactants such as "Pluronics ⁸ " generally provides a drying time which is substantially equivalent to the contact time between the gel and the biofilm which is necessary, required to destroy, eliminate the biofilm polluting the material. In other words, the formulation of the gel ensures a drying time which is none other than the time necessary to eliminate, destroy, the biofilm and which is compatible with the kinetics of destruction of the biofilm and in particular with the kinetics of destruction of biological contamination contained in the biofilm (biological organisms are killed). After the drying of the gel, the gel fractures homogeneously to give millimetric solid dry residues, for example of a size of 1 to 10 mm, preferably 2 to 5 mm non-pulverulent, generally in the form of solid glitter. The dry and solid residues contain compounds resulting from the destruction of the biofilm.

Dry residues, such as flakes, obtained after drying have a poor adhesion to the surface of the cleaned material. As a result, the dry residues obtained after drying of the gel can be easily recovered by simple brushing and / or aspiration. However, the dry residues can also be evacuated by gas jet, for example by compressed air jet.

Thus, no rinsing is necessary and the process according to the invention does not generate any secondary effluent.

According to the invention, thus first of all an important economy of chemical reagents is achieved with respect to a decontamination method by washing with a solution. Then, since a waste in the form of a directly aspirable dry residue is obtained, a rinsing operation with water or with a liquid is avoided. This obviously results in a decrease in the amount of effluents produced but also a significant simplification in terms of treatment and outlet channel. In particular, according to the invention, the waste obtained at the end of the treatment is not entrained in the rainwater drainage networks in violation of the regulations.

Due to the predominantly mineral composition of the gel used according to the invention and the small amount of waste produced, the dry waste can be stored or directed to a discharge die without prior treatment.

For example, in the current case where 1000 grams of gel are applied per m ² of treated surface, the mass of dry waste produced is less than 300 grams per m ² .

The invention will now be described with reference to the following examples, given by way of illustration and not limitation. Examples:

Example 1

In this example, the "anti-biofilm" gel studied in Examples 2 and 3 below is described and prepared.

It is a mineral, basic, alkaline, oxidizing gel comprising water, 1M sodium hydroxide, sodium hypochlorite, alumina, and a surfactant.

This gel does not include superabsorbent polymer.

Alumina is alumina Aeroxide ^* Alu C marketed by EVONIK INDUSTRIES with a specific surface area of 100 m ² / g (BET), the surfactant is the surfactant Pluronic ^* PE6200 marketed by BASF, the soda is 1M sodium sold by SIGMA-ALDRICH, and sodium hypochlorite is sodium hypochlorite 10 to 15% active chlorine, marketed by SIGMA-ALDRICH.

The gel used according to the invention is prepared as follows: the sodium hypochlorite solution is diluted to 50% with deionized water. This solution, the surfactant, and the sodium hydroxide are then mixed using a mechanical stirrer equipped with a stirrer with three blades, at a speed of 200 rotations / min, for 3 to 5 minutes. The alumina is then gradually added to the reaction mixture, gradually increasing the stirring speed as the viscosity increases, to arrive at about 400 to 600 revolutions / min without projections. . The gel is then stirred for 5 minutes.

The composition of the gel studied is given in Table 2 below.

Table 2: Composition of the studied gel.

Composition Percentages by mass (%) NaOH 1M 44.5

Sodium hypochlorite (10-15% a.c.) diluted 50% 42.5

Alumina 12

Pluronic ^" PE6200 1

Example 2 In this example, a test is carried out with the "anti-biofilm" gel prepared in Example 1 to remove a biofilm on a vertical outer surface.

The "anti-biofilm" gel prepared in Example 1 is applied by brush to a portion of the surface of an outer wall coated with a traditional spray coating.

The test takes place at a temperature below 10 ° C, and with a relative humidity of the order of 50%.

After 48 hours of drying, the flakes formed are removed by gentle brushing. FIG. 1 (A, B, C) shows the appearance of the wall surface during the different stages of the test carried out in this example, namely:

the initial state of the wall surface (A);

the appearance of the surface of the wall after application of the gel with a brush on a part of the surface of the wall, this part of the surface of the wall is thus covered with wet gel (B);

the appearance of the surface after drying for 48 hours and removal of dry gel flakes by gentle brushing (C).

It is visually apparent that the biofilm was effectively removed from the treated wall surface portion, cleaned in accordance with the invention, using the gel prepared in Example 1.

This test shows the effectiveness of the use according to the invention of the alkaline oxidizing gel prepared in Example 1 to remove a biofilm on a vertical surface.

In order to better quantify the action of the gel, an image analysis was carried out using the ImageJ software.

To do this, the final image of FIG. 1C, which thus shows the surface of the wall at the end of a treatment according to the invention, has been converted into gray levels (on a scale ranging from 0, black, to 255 , white) and an analysis of the gray values was carried out along the line shown in Figure 2A (similar to Figure 1C).

The average value in that portion of the non-gel treated wall surface of Example 1 is taken as a reference. The graph of FIG. 2B shows the results of the image analysis, and confirms the effectiveness of the removal of the biofilm by the gel in the part of the surface of the wall treated according to the invention by the gel prepared in FIG. Example 1. Example 3.

In this example, a test is carried out with the "anti-biofilm" gel prepared in Example 1 to remove a biofilm on a horizontal outer surface.

The "anti-biofilm" gel prepared in Example 1 is applied by brush to a portion of the surface of a white cement balcony railing.

After 48 hours of drying, the flakes formed are removed by gentle brushing. FIG. 3 (A, B, C, D) shows the appearance of the surface of the railing during the various stages of the test carried out in this example, namely:

- the initial state of the surface of the railing (A);

the appearance of the surface of the railing after application of the gel with a brush on a part of the surface of the railing, this part of the surface of the railing is thus covered with wet gel (B);

the appearance of the surface after drying for 48 hours of the gel applied on a part of the surface of the railing, this part of the surface of the railing is thus covered with dry gel (C);

the appearance of the surface of the railing after removal of dry gel flakes by gentle brushing (D). It is visually apparent that the biofilm was effectively removed from the portion of the surface of the treated railing, cleaned in accordance with the invention, using the gel prepared in Example 1.

This test shows the effectiveness of the use according to the invention of the alkaline oxidizing gel prepared in Example 1 to remove a biofilm on a horizontal surface. In order to better quantify the action of the gel, an image analysis was carried out using the ImageJ software, as in Example 2.

For this purpose, as in example 2, the final image of FIG. 3D which thus shows the surface of the railing at the end of a treatment according to the invention has been converted into gray levels (on a scale ranging from 0, black, to 255, white).

On the other hand, the difference being less marked (strong background noise), the result is expressed in gray level averaged over two areas of the surface of the railing, a first area 41 being located in the part of the surface treated by the gel and a second zone 42 being located in the portion of the surface not treated with the gel (Figure 4).

It is noted that the untreated area has an average level of 156 while the treated area has a mean gray level of 169.

The results of the image analysis confirm the effectiveness of the removal of the biofilm by the gel in the part of the surface of the rail treated according to the invention by the gel prepared in Example 1.

REFERENCES

[1] NOBATEK report:

http: //www.nobatek om / downloads / Studies% 20publics / ENSEL% 20Micro% 20biology

% 20_N OBATEK_.pdf

[2] US-A1-2012 / 0232153.

[3] "Biofilm when microbes get organized" by R. Briandet, L. Fechner, M. Naïali and

C. Dreano, Editions Quae 2012.

[4] K. Ammerman, "Algae, the growing problem," Interface, January 2007, pages 37-42.

[5] FAURE S., FOURNEL B., FUENTES P., LALLOT Y. "Method of treating a surface with a treatment gel, and treatment gel", FR-A1-2 827 530.

[6] FAURE S., FUENTES P., LALLOT Y. "Aspirable gel for the decontamination of surfaces and use", FR-A1-2 891 470.

[7] CUER F., FAURE S. "Biological decontamination gel and method for decontaminating surfaces using this gel", FR-A1-2962046 and

WO-A1-2012 / 001046.

Claims

1. Use of a gel constituted by a colloidal solution comprising, preferably consisting of:

- 0.1% to 2% by weight relative to the mass of the gel, at least one surfactant;

and a solvent;

and the gel not containing superabsorbent polymer;

to remove a biofilm on a surface of a solid substrate.

2. Use according to claim 1, wherein the mineral base is chosen from sodium hydroxide, potassium hydroxide, and mixtures thereof, and the stable oxidizing agent in basic medium is selected from hypochlorites, and mixtures thereof. .

3. Use according to claim 2, wherein the gel contains a combination of sodium hydroxide and sodium hypochlorite.

4. Use according to any one of the preceding claims, wherein the inorganic viscosifying agent is selected from metal oxides such as aluminas, metalloid oxides with the exception of silica, metal hydroxides, hydroxides metalloids, metal oxyhydroxides, metalloid oxyhydroxides, aluminosilicates, clays such as smectite, and mixtures thereof.

5. Use according to claim 4, wherein the inorganic viscosifying agent consists of one or more alumina (s).

6. Use according to claim 5, wherein the alumina (s) represent (s) from 5% to 30% by weight, preferably from 8% to 17% by weight relative to the total mass of the gel.

The use according to any one of the preceding claims, wherein the surfactant is selected from nonionic surfactants such as block copolymers, sequenced such as block copolymers of ethylene oxide and propylene oxide, and ethoxylated fatty acids; and their mixtures.

8. Use according to any one of the preceding claims, wherein the solvent is selected from water, organic solvents, and mixtures thereof.

Use according to any one of the preceding claims, which further comprises one or more inorganic pigment (s).

10. Use according to any one of the preceding claims, wherein the substrate is in at least one material selected from metals and alloys such as stainless steel, galvanized steel, or zinc; painted steels; organic polymers such as plastics or rubbers such as polyvinyl chloride or PVC, polypropylenes or PPs, polyethylenes or PEs, in particular high density polyethylenes or HDPEs, poly (methyl methacrylates) or PMMA, poly (fluoride of vinylidene or PVDF, polycarbonates or PCs; the glasses ; cementitious materials such as pastes, cements, mortars and concretes; plasters; the bricks ; tiles ; raw or cooked earth; natural or artificial stones; coatings; fiberglass; fibrocement; asphalt; tar ; slate; cellulose-based materials such as wood; and ceramics.

11. Use according to any one of the preceding claims, in which at least one cycle is carried out comprising the following successive steps:

a) the gel is applied to said surface;

b) the gel is maintained on the surface for at least sufficient time for the gel to destroy the biofilm, and for the gel to dry and form a dry, solid, non-powdery residue containing compounds resulting from the destruction of the biofilm;

12. Use according to claim 11, wherein the gel is applied to the surface of the solid substrate in a proportion of 100 g to 2000 g of gel per m ² of surface, preferably of 500 g to 1500 g of gel per m ² of surface, more preferably from 600 g to 1000 g of gel per m ² of surface.

13. Use according to any one of claims 11 and 12, wherein the gel is applied to the surface of the solid substrate by spraying, brushing, or with a trowel.

14. Use according to any one of claims 11 to 13, wherein in step b), the drying is carried out at a temperature of 1 ° C to 50 ° C, preferably 15 ° C to 25 ° C and at a relative humidity of 20% to 80%, preferably 20% to 70%.

15. Use according to any one of claims 11 to 14, wherein the gel is held on the surface for a period of 2 to 72 hours, preferably 2 to 48 hours, more preferably 3 to 24 hours.

16. Use according to any one of claims 11 to 15, wherein the dry and solid residue is in the form of particles, for example flakes, of a size of 1 to 10 mm, preferably 2 to 5 mm.

17. Use according to any one of claims 11 to 16, wherein the dry and solid non-pulverulent residue is removed from the surface of the solid substrate by brushing and / or aspiration.

Use according to any one of claims 11 to 17, wherein the described cycle is repeated from 1 to 10 times using the same gel in all cycles or using different gels in one or more cycles. (s).

19. Use according to any one of claims 11 to 18, wherein, in step b), the gel, before total drying, is rewetted with a mineral base solution and oxidizing agent, preferably with the solution of mineral base and oxidizing agent applied during step a) in the solvent of this gel.