Stable gels with low concentrations of peracetic acid for the application of biocidal treatment to surfaces.

Abstract

The invention relates to an aqueous-based gel having an apparent pH between 3 and 6, characterized in that it comprises: between 1.5 and 6% by mass relative to the total gel mass of one or a mixture of organic thickener(s) including microcrystalline cellulose; between 0.005% and 1% by mass relative to the total gel mass of peracetic acid; and between 0.3% and 3% by mass relative to the total gel mass of casein. It exhibits a stability over time of at least two months. The invention also relates to a method for adjusting the pH of these stable gels and their use for biocidal treatments. The gel according to the invention, comprising approximately 0.020% APA, is particularly useful for treating stone surfaces, and more specifically for limestone sculptures. Figure for the summary: Fig.4: Partial view of a limestone sculpture before treatment and six months after treatment.

Description

Title of the invention: Stable gels with low dosage of per-acetic acid for the application of a biocidal treatment on surfaces.

[0001] The present invention relates to a novel and stable gel having an apparent pH between 3 and 6, comprising peracetic acid (PAA), an organic thickener, and casein. It also relates to a method for adjusting the pH of such a gel and to the use of such gels as cleaners and biocides in the fields of disinfection, maintenance, and hygiene. They are particularly suitable for use in outdoor biocidal treatments. They are designed for use in treating stone monuments and statues in gardens. The present invention also relates to the use of these gels as a preventative biocide after manual moss removal or weeding.

[0002] Few biocidal active substances exhibit a complete spectrum of activity (virucidal, bactericidal, fungicidal, and sporicidal). However, sporicidal activity is a required property for outdoor applications. Furthermore, there is a need for a product that functions in the presence of complex soiling (air pollution containing organic, inorganic, and metallic residues – Cu, Zn, Pb). Finally, there is a need for a product or product family that does not disperse biocidal substances into the environment, nor any hazardous substances.

[0003] Hypochlorites are complete biocides. However, it is known that many substrates cannot be treated with this substance. (1) Most metals in contact with hypochlorites are oxidized; (2) Chloride ions are responsible for long-term degradation through penetration and action on metallic structures; (3) The generation of sodium chloride, or table salt, is harmful to stone.

[0004] Quaternary ammonium compounds are widely used, but they have the disadvantage of persisting and accumulating in soils and water. They also release their counter-ions, chloride ions, into the environment. These often have a detrimental effect, as described above.

[0005] As described in the document from the Coordination Center for the Fight Against Nosocomial Infections of the Southeast Inter-region, "Peracetic acid: activities and use in healthcare facilities," dated January 20, 2005, peracetic acid exhibits bactericidal, fungicidal, sporicidal, and virucidal activity at low concentrations, although this activity is modulated by temperature, pH, the presence or absence of hydrogen peroxide, and contact time. For example, sporicidal activity against Bacillus subtilis spores is described therein in one hour at a concentration of 42 ppm (0.0042%) of peracetic acid in the presence of 0.56% hydrogen peroxide. Peracetic acid has the particularity of being a residue-free biocide. toxic. Its use remains limited partly due to the instability of diluted APA solutions.

[0006] Diluted solutions to be prepared before use are commercially available, but they contain soluble salts incompatible with stone monuments.

[0007] Self-degradable two-component oxidizing gels based on different oxidants are described in patent FR 3089753. However, these types of gels prepared on the basis of APA are excluded because the formation of a white veil has been observed on the treated limestones.

[0008] Therefore, there is a real need to develop a new formulation of APA-based gels compatible with stones, and with limestone in particular. Furthermore, in order for this gel to be usable and marketed, we need a stable APA-based gel that remains stable for at least two months.

[0009] For the purposes of this text, a stable APA-based gel is defined as a gel that retains its homogeneity for at least two months (or easily regains it after shaking) and has an APA content exceeding 90% of the APA percentage measured immediately after preparation. Furthermore, its viscosity at two months is at least 0.1 Pa·s for a shear stress of 1 s⁻¹.

[0010] This goal, and others, are achieved by the present invention.

[0011] The first object of the invention relates to an aqueous-based gel having a pH apparent, between 3 and 6, characterized in that it comprises: - Between 0.5 and 6% by mass relative to the total mass of the gel of one or a mixture of organic thickener(s) - Between 0.005% and 1% by mass relative to the total mass of the peracetic acid gel - Between 0.3% and 3% by mass relative to the total mass of the casein gel

[0012] All percentages indicated in this document are mass percentages expressed relative to the final total mass of the gel.

[0013] The term gel refers to a colloidal dispersion which exhibits the properties of a physical gel (presence of a network and viscoelastic behavior).

[0014] The apparent pH of the gel is the value obtained by direct reading with a glass electrode or with the aid of a colored indicator of pH paper or by any other method.

[0015] The pH of the gel of the invention is between 3 and 6.

[0016] In some embodiments, the pH of the gel of the invention is controlled by a a buffer system to be maintained between 3 and 6. For this, a mixture of weak acid(s) and salt(s) of the acid(s) can be used. In some embodiments, the weak acid comprises acetic acid. The salt will comprise sodium, calcium, ammonium, magnesium, etc. ions. It will preferably be calcium-based and / or magnesium.

[0017] Mixtures comprising other weak organic acids, having one or more carboxylic acid groups, may also be used. Examples include, but are not limited to, citric acid, tartaric acid, etc.

[0018] In embodiments a strong soluble base is used to adjust the pH, in an amount less than 0.02% by mass of the final gel, preferably less than 0.01% by mass of the final gel.

[0019] In embodiments, the pH of the gel can be adjusted by acetic acid or magnesium oxide or a mixture of both.

[0020] In some embodiments, magnesium oxide comprises basic magnesium hydroxide (CAS 39409-82-0).

[0021] In some embodiments, magnesium oxide comprises magnesium hydroxycarbonate (CAS 12125-28-9).

[0022] Throughout the remainder of this document, an organic thickener is defined as a compound or mixture of organic compounds that has the property of increasing the viscosity of an aqueous mixture when added to it, at concentrations of the thickener between 0.5 and 6%, preferably between 0.5 and 4%, preferably between 1.5 and 6%, and preferably between 1.9 and 4%. Furthermore, this thickening agent may be natural or synthetic.

[0023] In embodiments, the organic viscosifiers may be chosen from the following list, without this list being exhaustive: polyacrylics, polyacrylamides, crosslinked or not, polysaccharides, PEGs, and mixtures thereof.

[0024] Here and throughout the rest of the text, polysaccharides means all natural polysaccharides and their derivatives.

[0025] In embodiments, the gel of the invention comprises one or more polysaccharides as organic viscosifier(s).

[0026] In embodiments, the polysaccharide(s) is / are chosen from cellulose and its derivatives, hemicellulose and its derivatives, chitin and its derivatives, agar-agar and its derivatives, carrageenan and its derivatives, pectin, gums (xanthan, guar) and their sodium, potassium, and calcium salts, xanthan gum, starch and its derivatives, dextrin and mixtures thereof.

[0027] In embodiments, cellulose and its derivatives include, but are not limited to, cellulose, microcrystalline cellulose, hydroxypropylcellulose, hydroxyethylcellulose, carboxymethylcellulose, sodium carboxymethylcellulose and mixtures thereof.

[0028] In some embodiments, mixtures of microcrystalline cellulose and cellulose gum will be chosen. Preferably, these mixtures will be stable at pH levels from 3 to 10.

[0029] Cellulose gum means carboxymethylcellulose or its sodium derivative or a mixture of the two.

[0030] In embodiments, mixtures comprising cellulose and hydroxyethylcellulose will be chosen.

[0031] Peracetic acid means the compound designated by CAS No. 79-21-0.

[0032] In embodiments, peracetic acid is present at sufficiently limited concentrations so that the gel is not classified as an organic peroxide; APA is therefore present in the gel of the invention at concentrations between 0.005% and 1%, preferably at concentrations between 0.01% and 0.5%, preferably at concentrations between 0.01% and 0.2%, preferably again at concentrations between 0.01% and 0.1%, preferably at concentrations between 0.01% and 0.04%, preferably again at concentrations between 0.01% and 0.03%.

[0033] In embodiments, solutions comprising APA are added to a gelled preparation.

[0034] A gelled preparation is understood to be a colloidal dispersion which has the properties of a physical gel (presence of a network and viscoelastic behavior).

[0035] In embodiments, a freshly diluted commercial APA solution is added to a gelled preparation.

[0036] Several commercial sources of APA can be cited, without this list being exhaustive: Acidofoam CF, Contée Peridox RTU, Peracetique 2% Hydra, Anios 1000, Anios twin, Sanitol stain remover.

[0037] In some embodiments, the APA present in the gel of the invention was generated in situ.

[0038] In embodiments the solution containing APA is added to the gelled preparation after being produced in situ.

[0039] In embodiments, peracetic acid is generated in situ in the gel of the invention.

[0040] Peracetic acid can be generated in situ in various ways. Examples include, but are not limited to: the reaction of hydrogen peroxide and / or sodium percarbonate with a peracetic acid precursor.

[0041] A precursor of peracetic acid is understood to be any molecule which, under the action of 5%, 12% and / or 30% hydrogen peroxide, generates peracetic acid.

[0042] In embodiments the peracetic acid precursor is contained in the gelled preparation.

[0043] In embodiments, APA is added to a gelled preparation after being produced in situ from a peracetic acid precursor and hydrogen peroxide.

[0044] In some embodiments, the APA is generated in situ by adding hydrogen peroxide to a gelled preparation already containing the peracetic acid precursor. The proportion of precursor relative to the final gel is 0.1 to 3%, preferably 0.1% to 0.5%, preferably 0.1% to 0.33%.

[0045] In some embodiments, the APA is generated in situ by adding one or more peracetic acid precursors to a gelled preparation containing hydrogen peroxide. This precursor is present at concentrations ranging from 0.1 to 2%, preferably from 0.1% to 0.5%, preferably from 0.1% to 0.33%.

[0046] In embodiments the precursor of peracetic acid is acetic acid, triacetin or 1,3 diacetyloxypropane-2-ylacetate (cas 102-76-1), tetraacetyldiamine (cas 10543-57-4)), acetylcaprolactam (cas 1888-91-1).

[0047] In embodiments the peracetic acid precursor comprises trie-ethylcitrate (cas 77-93-0).

[0048] Preferably the precursor of peracetic acid is triacetin.

[0049] In embodiments, triacetin is introduced into the gel at concentrations ranging from 0.1 to 5%, preferably at concentrations of 0.8 to 2% (by mass relative to the total mass of the final gel).

[0050] In embodiments the solution containing APA is generated in situ by adding triacetin to a solution comprising 34.9% hydrogen peroxide before being added to a gelled preparation.

[0051] In embodiments the solution containing APA is generated in situ by adding triacetin to a solution comprising 12% hydrogen peroxide before being added to a gelled preparation.

[0052] In embodiments the temperature during the formation of APA in situ is between 12 and 30°C, preferably between 15 and 25°C.

[0053] In embodiments, APA is generated in situ in the gel in the presence of triacetin and 5% H2O2.

[0054] In certain embodiments, and when the gel contains hydrogen peroxide, its APA concentration can be 'regenerated' by adding an APA precursor to the gel after 2 months, preferably after 4 months, and preferably after 6 months. Extending the shelf life of the gels in this way constitutes a further advantage of the invention.

[0055] In embodiments, 0.8 to 2% triacetin will be added to the gel.

[0056] Casein is a binder used by restorers of historical monuments in compresses that allows for less penetration into limestone. It is quite surprising, and this is one of the objects of the invention, that casein can coexist with APA within a gel.

[0057] Casein is introduced into the gelled preparation. It is present in the gel of the invention at concentrations between 0.1 and 5%, preferably at concentrations between 0.3 and 3%, preferably between 0.3 and 2%, preferably between 0.5 and 1%.

[0058] Quite surprisingly, while dilute peracetic acid solutions (between 0.01 and 0.12%) are known to be stable for 7 to 15 days, the gels of the invention with dilute concentrations of peracetic acid have demonstrated stability for at least two months, and even for four months, six months, or more. The first surprising point is the persistence of the peracetic acid over time. The second point concerns the persistence of the mixture's organization in gel form.

[0059] In embodiments the gel further comprises hydrogen peroxide, preferably between 0.5% and 15%, preferably between 0.5% and 12%, preferably again between 0.5% and 5%, preferably between 1% and 5%, preferably between 3% and 5%.

[0060] In some embodiments, this proportion of hydrogen peroxide in the gel will be between 11 and 12%

[0061] In some embodiments, this proportion of hydrogen peroxide in the gel will be between 4 and 5%

[0062] In some embodiments, hydrogen peroxide is stabilized.

[0063] In some embodiments, the stabilizers of hydrogen peroxide are disodium pyrophosphate, phosphoric acid and ammonium nitrate and mixtures thereof.

[0064] In some embodiments, the introduced hydrogen peroxide is stabilized by urea.

[0065] In some embodiments, the freezing of the invention further comprises between 1 and 3% Urea; urea can be added to the mixture as a hydrogen peroxide stabilizer or as a constituent of its own. The urea present in the gel contributes to the stabilization of the APA present in the gel.

[0066] The speed of action of the gels of the invention can be modulated according to their composition, and their proportions in organic agent or in mineral agent.

[0067] In order to modulate the affinity of the gel for its support, mineral components can be added to the gel.

[0068] In embodiments, these mineral components will not be soluble at a pH of 6 or greater than 6.

[0069] In embodiments, the gels of the invention shall comprise alumina.

[0070] In embodiments, the gels of the invention shall contain up to 4% boehmite.

[0071] In embodiments, boehmite comprises up to 3%, preferably up to 1%, of nitric acid.

[0072] In embodiments, the gel of the invention also comprises up to 2% of a non-ionic surfactant, preferably between 0.1 and 1%, preferably between 0.2% and 0.8%, preferably again between 0.1 and 0.2%.

[0073] For example, a surfactant or mixtures thereof may be used from the following list, without this list being exhaustive: of the alkylpolyglucoside or hni-dazoline type, of the propylene oxide and ethylene oxide polymer block type such as surfactant PE6200 (BASF, registered trademarks), surfactant Pantacare 12000 UR (BASF, registered trademarks), surfactant DPE 201 (Lankem, registered trademarks), or a sorbitan derivative such as surfactant Lansurf SMO (Lankem, registered trademarks) or Lansurf SMO 80 (Lankem, registered trademarks).

[0074] The presence of this surfactant may improve the cleaning properties of the gel of the invention.

[0075] Quite surprisingly, it is possible to add up to 10% of an organic solvent to the gel without losing the properties specific to the invention; the presence of this element makes it possible in particular to modify the cleaning character of the gel of the invention and to modulate its drying speed.

[0076] In embodiments the organic solvent(s) will be chosen from among esters, for example and without this list being exhaustive butyldiglyco-lacetate, butylglycolacetate, glyceroltriacetate, volatile esters of fatty acids, for example and without this being exhaustive ethyl oleate.

[0077] The gels of the invention are prepared using any method that allows the particles to be dispersed in the liquid phase(s). Those skilled in the art know how to use the appropriate equipment. Preferably, mechanical stirring is used; preferably, the casein and then the organic thickener or the mixture of organic thickeners are added to the water; preferably, the surfactant is added after the organic thickener; preferably, the alumina is added next. The solvent is then added, as well as the APA precursor(s). The pH of the gelled preparation thus prepared may optionally be adjusted to 6 or 7 before the addition or formation of APA in the gel. Depending on the waiting time before use and the nature of the material being treated, the pH of the gel may or may not be readjusted at the time of use.

[0078] In preparation methods, the gelled preparations based on polysaccharides and casein shall further comprise hydrogen peroxide so as to be able to be stored. Preferably they shall comprise between 0.1 and 0.5% hydrogen peroxide, preferably between 0.1 and 0.2% hydrogen peroxide.

[0079] In some embodiments the pH of the gel just after preparation is 6.

[0080] The second object of the invention consists of adjusting the pH of the gel of the invention to a specific pH just before its use by using a base or an acid.

[0081] In embodiments, the resulting gel will have a pH between 6 and 9, preferably between 6 and 8, preferably the pH will be 7.

[0082] In some embodiments, the resulting gel will have a pH between 6 and 7 for at least 5 days, preferably at least 10 days.

[0083] In embodiments the base used is a base that is slightly soluble at pH values ​​above 7 and more soluble at acidic pH values ​​(<7).

[0084] In some embodiments this base comprises basic magnesium hydroxide.

[0085] In some embodiments this base comprises calcium hydroxide and / or calcium carbonate.

[0086] In embodiments the acid used comprises acetic acid, preferably at 8% in water.

[0087] Quite surprisingly, at 20°C the kinetics of the acid-base reactions in the gel over this pH range are sufficiently modified that we do not observe any heating when adding the acid or the base to the gel of the invention.

[0088] The modulation of this pH is an important element since it influences the intensity of the biocidal activity of the APA.

[0089] The third object of the invention is the use of the gels of the invention for the biocidal treatment of surfaces.

[0090] Gels have rheological properties that prevent them from spreading when poured onto a flat surface and from flowing when applied to an inclined or vertical surface. This property is essential for treating surfaces and significantly increasing contact times compared to a solution that would spread or flow.

[0091] The gels are further characterized using dynamic rheology. Thus, for application to a satisfactory vertical surface by brush, they will have a viscosity at a shear rate of 1 s⁻¹ of at least 0.1 Pa·s. For easy application, the viscosity at a shear rate of 100 s⁻¹ will not exceed 0.4 Pa·s. Viscosities are given at 25°C.

[0092] Treatment gels can be applied by roller, brush, paintbrush, or airless spray gun. They are then left on the surface for the time required for their action (between 15 minutes and 20 hours).

[0093] In some embodiments they are rinsed, with water or diluted lime water depending on the materials.

[0094] In some embodiments a film forms during drying; it can then be peeled off.

[0095] For biocidal treatment, it is recommended to first remove any existing plant material, which is easily removed. A layer of gel is applied and left to act for 4 to 24 hours. The residue is moistened with water under low pressure and then gently brushed before rinsing. A second application may be necessary to achieve the desired level of disinfection and / or residual effect.

[0096] In embodiments, and this is yet another quality of the use of gels with the invention, no recurrence of biological contamination was observed on the treated surfaces for at least one year.

[0097] The fourth object of the invention is the use of the gels of the invention for the preventive biocidal treatment of manually weeded surfaces.

[0098] Grass regrowth after manual weeding can be very rapid, on the order of one or two months. The use of the gels of the invention for treating these surfaces makes it possible to significantly increase the period before regrowth.

[0099] The fifth object of the invention is the use of the gels of the invention for the treatment of stone surfaces.

[0100] In embodiments, fouling related to pollution is treated by the gels of the invention.

[0101] In embodiments, the black crusts observed on stone surfaces are treated by the gels of the invention.

[0102] In embodiments, and for the treatment of stone surfaces, the gels of the invention shall have a pH, possibly adjusted before use if necessary, between 6 and 9, preferably between 6 and 7.

[0103] In some embodiments, the treated stones will be limestones or marbles.

[0104] The attached figures illustrate the invention:

[0105] [Fig. 1], groups together the photos of part of a limestone sculpture before and after treatment by freezing of the invention

[0106] [Fig.2], represents a marble surface before and after partial treatment with frost of the invention.

[0107] [Fig.3], groups together photos of the bottom of a wall before and after treatment by freezing the invention.

[0108] Fig. 4 shows photographs of part of a limestone sculpture before treatment and six months after treatment with the gel of the invention.

[0109] The invention will be better understood with reference to the following examples. This description is not exhaustive, as each feature of one embodiment can be advantageously combined with any other feature of any other embodiment.

[0110] The hydrogen peroxide and peracetic acid contents are determined by titration and trimetric titration, carried out respectively with potassium permanganate and sodium thiosulfate. (From Afssaps report - December 2007 - APA) These titrations are carried out at 19°C.

[0111] Viscosities are measured at 25°C. They were carried out with an A2000 ex rheometer (TA instruments, registered trademarks).

[0112] EXAMPLE 1 - Gel 15-155 according to the invention and use for treatment biocide for a limestone sculpture.

[0113] In a reactor equipped with mechanical stirring, 1289 g of water, 350 mg of 30% sodium hydroxide solution, 48.7 g of Cellulose Vivapur Cs Wet wipes (J. Rottenmaier & Sohne GMBH, registered trademarks), 11.4 g of PE6200 surfactant (BASF, registered trademarks), and 60.7 g of boehmite are loaded. The mixture is stirred for 1 hour. 17.2 g of casein and 70.1 g of butyl-diglycolacetate are added, and the pH is adjusted to 7 with 2.8 g of basic magnesium hydroxide.

[0114] In a container, 140 g of 34.9% hydrogen peroxide is placed. 3.59 g of triacetin is added. The mixture is shaken and left to act for 10 minutes at 15°C.

[0115] The oxidizing mixture (line 114) is added to 250g of the gelled preparation described in line 113.

[0116] The 15-155 gel described below is obtained:

[0117] [Tables] Viscosity, in Pa.s Apparent pH % H2O2 % APA t=0 to 100 if at 10 s1 to 1 s 1 to 0.1 s1 to 0.01 if 6 12.4% 0.13% 0.05 0.35 3.54 22.86 199.11

[0118] Fig. 1 presents part of a sculpture before and after treatment according to the rules of the art with freshly prepared 15-155 gel.

[0119] [Tables 2] Characteristic of the 15-155 gel over time: Time T0 2 months Appearance Gelled pH 6 3-4 %APA 0.13 0.13 %H2O2 12.4 11.6

[0120] EXAMPLE 2 - Method according to the invention of preparing gel 15-189 from gel 15-155 and using this gel for the treatment of a marble surface.

[0121] 575 g of 15-155 gel stored for 2 months are liquefied by gentle agitation. 8.86 g of basic magnesium carbonate (1.52% of the final gel) is added. This yields gel 15-189.

[0122] [Tables 3] Characteristic of the 15-189 gel Time T0 4 days 9 days Appearance gelled gelled PH 7 7 6-7 %APA. - - 0.11% %H2O2 - - 4.74%

[0123] Fig. 2 shows the detail of a marble surface before and after treatment with this gel.

[0124] EXAMPLE 3 - Gel 16-97 according to the invention

[0125] In a reactor equipped with mechanical stirring, 2175 g of water, 540 mg of 30% sodium hydroxide solution, 75.6 g of Vivapur Cs Cellulose Wet wipes (J. Rottenmaier & Sohne GMBH, registered trademarks), 17.7 g of PE6200 surfactant (BASF, registered trademarks), and 94.2 g of boehmite are loaded. The mixture is stirred for 1 hour. 24 g of casein are then added, followed by 8.2 g of 34.9% hydrogen peroxide.

[0126] In a container at 20°C, 7.08 g of urea is added to 52 g of 34.9% hydrogen peroxide. After dissolution, 3.75 g of triacetin is added. The mixture is shaken and left to act for 10 minutes at 20°C.

[0127] The oxidizing mixture (line 126) is added to 290g of the gelled preparation described in line 125. The pH is adjusted to 6 with 17.83 g of 8% acetic acid and 1.8 g of basic magnesium hydroxide.

[0128] The freezing of invention 16-97 is obtained.

[0129] [Tables4] Viscosity, in Pa.s Apparent pH % H2O2 % APA t=0 to 100 if at 10 s1 to 1 s1 to 0.1 s1 to 0.01 if 6 4.7% 0.017% 0.09 0.38 3.05 30.52 174.89

[0130] After 2 months of storage in an HDPE container at room temperature, the gel, once shaken, is perfectly homogeneous and exhibits the following characteristics:

[0131] [Tables5] Viscosity, in Pa.s Apparent pH % H2O2 % APA t=2 months at 100 if at 10 s1 at 1 s1 at 0.1 s1 at 0.01 if 5 4.7% 0.015% 0.19 0.72 1.24 10.7 150.9 EXAMPLE 4 - Gel 16-43OXY according to the invention and use for facade cleaning and biocide treatment of a limestone sculpture.

[0132] In a reactor equipped with mechanical stirring, 2032 g of water, 680 mg of 30% sodium hydroxide, 95 g of Cellulose Vivapur Cs Wet wipes (J. Rottenmaier & Sohne GMBH, registered trademarks), 22.23 g of PE6200 surfactant (BASF, registered trademarks), and 118.4 g of boehmite are loaded. The mixture is stirred for 1 hour. 37 g of casein, 154 g of butyldiglycolacetate, and 40 g of triacetin are added, and the pH is adjusted to 7 with 7.5 g of basic magnesium hydroxide.

[0133] In a container, 105 g of 34.9% hydrogen peroxide is placed. 7.03 g of triacetin is added. The mixture is shaken and left to act for 10 minutes at 19°C.

[0134] 500g of the gelled preparation described in line 132 is diluted with 125g of water. adds the oxidizing mixture described in line 133. The 16-43 OXY gel is obtained according to the invention, and described below.

[0135] [Tableauxô] Viscosity, in Pa.s Apparent pH % H2O2 % APA t=0 day at 100 if at 10 s1 at 1 s 1 at 0.1 s1 at 0.01 if 6 4.9% 0.019% 0.08 0.41 3.68 20.58 180.42

[0136] Fig. 3 brings together photos of the bottom of an exterior wall before and after treatment with this 16-43 OXY gel.

[0137] Fig. 4 brings together photos of part of a limestone sculpture before treatment and six months after treatment with this 16-43 OXY gel.

Claims

Demands

1. Aqueous-based gel having a pH between 3 and 6 and characterized in that it comprises: - Between 1.5% and 6% by mass relative to the total mass of the gel of one or a mixture of organic thickener(s) comprising microcrystalline cellulose - Between 0.005% and 1% by mass relative to the total mass of the peracetic acid gel - Between 0.3% and 3% by mass relative to the total mass of the casein gel

2. Gel according to the preceding claim, wherein the organic thickener further comprises one or more other polysaccharide(s)

3. Gel according to claim 2 wherein the polysaccharide(s) comprises (ent) cellulose and / or one or more of its derivatives.

4. Gel according to any one of the preceding claims wherein the organic thickener(s) comprises (they) between 1.9% and 4% of a mixture of microcrystalline cellulose and cellulose gum.

5. Gel according to any one of the preceding claims wherein peracetic acid is generated in situ by a peracetic acid precursor

6. Gel according to the preceding claim wherein the peracetic acid precursor comprises triacetin

7. Gel according to any one of the preceding claims further comprising between 11 and 12% hydrogen peroxide

8. Gel according to any one of the preceding claims further comprising between 4 and 5% hydrogen peroxide

9. Gel according to any one of the preceding claims further comprising between 1 and 3% urea

10. Gel according to any one of the preceding claims further comprising acetic acid and magnesium oxide

11. Gel according to any one of the preceding claims further comprising up to 4% boehmite

12. Gel according to any one of the preceding claims further comprising between 0.1 and 1% of a non-ionic surfactant.

13. Gel according to any one of the preceding claims further comprising up to 10% organic solvent.

14.

15.

16.

17.

18. Method for adjusting the pH of a gel according to one of the preceding claims with a base A fitting method according to claim 14 with a base comprising basic magnesium hydroxide Use of the gels described in claims 1 to 15 for the biocidal treatment of a surface Use of the gels described in any one of claims 1 to 15 for the treatment of stone surfaces. Use of the gels described in any one of claims 1 to 15 for the treatment of limestone or marble surfaces.

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