Technical field of the invention

The present invention relates to cleaning compositions. More specifically, the invention relates to cleaning compositions with preservative effect for cleaning offshore wind turbines.

Background of the invention

Wind turbines are subject to continued pollution. These contaminants are partly due to assembly and transport dirt, but is also generated from oil leaks from the nacelle flowing down the tower. However, especially for offshore wind turbines, most of the contamination are airborne contaminants (including feces of birds). Microorganisms (including algae, fungi and lichens) then secondarily colonize the contaminants.

The contaminants excreted by the organisms of secondary colonization pose a considerable risk of corrosion for wind turbines, particularly in the offshore area, where the air is very moist and saline. Furthermore, the contamination increases the noise from the wind turbines, and result in a negative aesthetic impression.

For these reasons, it is necessary to clean the entire offshore wind turbine several times a year. The cleaning of offshore wind turbines is very expensive. The cleaning is performed manually, e.g. using lifts. This approach requires considerable labor, time and cost.

Summary of the invention

One object of the present invention is to reduce or retard the colonization of microorganisms on offshore wind turbines.

The inventor have found that a cleaning/coating composition comprising a combination of wax and a considerable amount of an organic acid will prolong the surface resistance to colonization of microorganisms onto an offshore wind turbine. The cleaning composition also comprises a surfactant for better cleaning of the surface, as well as for mixing the wax and the or- ganic acid. When applied to an offshore wind turbine, the mixture of wax and organic acid form a surface coating thereon. The organic acid then slowly diffuses out of the wax, thereby killing colonized microorganisms, and prevent new ones from settling. In the present context, the meaning of "microorganisms" includes, but is not limited to, bacteria, fungi, algae, and protozoans.

One aspect relates to the use of a cleaning composition comprising wax, surfactant, organic acid, and at least one solvent for cleaning a wind turbine, wherein the solvent is selected from the group consisting of water, an alcohol, or mixtures thereof.

A second aspect relates to the use of a cleaning composition comprising wax, surfactant, organic acid, and at least one solvent for cleaning an off- shore structure positioned above the sea level, wherein the solvent is selected from the group consisting of water, an alcohol, or mixtures thereof.

A third aspect relates to a cleaning composition comprising a wax, surfactant, organic acid, and at least one solvent, wherein the solvent is selected from the group consisting of water, an alcohol, or mixtures thereof.

Preferably, the solvent is water, since it aids in the forming of an emulsion of wax-organic acid-surfactant droplets. In one or more embodiments, the cleaning composition comprises solvent, preferably water, in an amount of 10-96% vol/vol, such as within the range of 15-90% vol/vol, e.g. within the range of 20-85% vol/vol, such as within the range of 25-80% vol/vol, such as within the range of 30-75% vol/vol, e.g. within the range of 35-70% vol/vol, such as within the range of 40-65% vol/vol, e.g. within the range of 45-60% vol/vol, such as within the range of 50-55% vol/vol.

Too much organic acid may damage the surface of the offshore structure due to its corrosive properties, and too little will not result in long-term protection from microorganisms. The use of inorganic acid did not result in in long-term protection from microorganisms. Without being bound by any theory, it is speculated that it is difficult to incorporate the inorganic acid in the surfactant droplets. Furthermore, the organic acid is thought in itself to be antimicrobial. In one or more embodiments, the cleaning composition comprises organic acid in an amount of 0.5-5% vol/vol, such as within the range of 0.75-4.75% vol/vol, e.g. within the range of 1.00-4.50% vol/vol, such as within the range of 1.25-4.75% vol/vol, e.g. within the range of 1.00-4.25% Vol/vol, such as within the range of 1.50-4.00% vol/vol, e.g. within the range of 1.75-3.75% vol/vol, such as within the range of 2.00-3.50% vol/vol, e.g. within the range of 2.25-3.25% vol/vol, such as within the range of 2.50-3.00% vol/vol.

In one or more embodiments, the cleaning composition comprises organic acid in an amount of 0.5-3% vol/vol, such as within the range of 0.75-2.75% vol/vol, e.g. within the range of 1.00-2.50% vol/vol, such as within the range of 1.25-1.75% vol/vol.

There seems to be a minimum limit to the amount of acid that can be present in the wax or wax containing droplet for the acid to diffuse to the sur- face of the coating. At the same time, there seems to be a maximum limit on how much acid that can be incorporated in the wax or wax containing droplet.

In one or more embodiments, the volume ratio between the organic acid and the wax is within the range of 1 :1-1 :20, e.g. within the range of 1 :1.5- 1 :15, such as within the range of 1 :1.75-1 :14, e.g. within the range of 1 :2- 1 :13, such as within the range of 1 :2.25-1 :12, e.g. within the range of 1 :2.5- 1 :11 , such as within the range of 1 :2.75-1 :10, e.g. within the range of 1 :3- 1 :9, such as within the range of 1 :3.25-1 :8, e.g. within the range of 1 :3.5- 1 :7, such as within the range of 1 :375-6, e.g. within the range of 1 :4-1 :5, preferably within the range of 1 :1 25-1 :5.

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Without being bound by any theory, it is speculated that the mode of action of an organic acid is that the non-dissociated acids penetrate the microorganism cell wall via passive diffusion and disrupt the normal physiology of the cell in two ways. The acids dissociate and therefore lower the internal pH, which is normally close to neutral, impairing the function of the microorganism. The anionic part of the acid, that is unable to leave the cell in its dissociated form, accumulates within the cell, disrupting metabolic functions and increasing osmotic pressure.

In one or more embodiments, the organic acid is selected from the group consisting of citric acid, benzoic acid, propionic acid, tartaric acid, acetic acid, oxalic acid, malic acid, salicylic acid, lactic acid, gluconic acid, hydroxyacetic acid, and mixtures thereof.

As used herein, the term "organic acid" is also referring to its salt.

It has been discovered that using combinations of at least two organic acids or their salts, provides synergistic microbial control.

In one or more embodiments, the organic acid is a mixture of at least two different organic acids selected from the group consisting of citric acid, benzoic acid, propionic acid, tartaric acid, acetic acid, oxalic acid, malic acid, salicylic acid, lactic acid, gluconic acid, hydroxyacetic acid, and mixtures thereof.

The selection of the organic acid may be dependent on the chosen type of wax and vice versa.

The wax

In one or more embodiments, the wax is selected from the group consisting of a vegetable wax, a mineral wax, a natural wax, an animal wax, a synthetic wax, and mixtures thereof.

Vegetable waxes may be candellila wax, ouricury wax, carnauba wax, orange-peel wax, japan wax, and bayberry wax

Mineral waxes may be montan wax, paraffin, and microcrystalline waxes.

Natural waxes may be beeswax, hydrogenated castor oil wax, and hydro- genated oils.

Animal waxes may be spermaceti wax.

Synthetic waxes may be polyethylene wax, polypropylene wax, polyamide wax, and silicone waxes. Synthetic waxes can provide a durable, protective coating that can equal or exceed the protection of the natural materials. The former include petroleum-derived and other synthetic materials such as ceresine, ozokerite, paraffin, microcrystalline, polyethylene waxes, Fischer- Tropsch waxes, fluorocarbons and silicones such as dimethiconol hydrox- ystearate. In one or more embodiments, the cleaning composition comprises wax in an amount of 0.5-50% vol/vol, such as within the range of 1-45% vol/vol, e.g. within the range of 5-40% vol/vol, such as within the range of 10-35% vol/vol, such as within the range of 15-30% vol/vol, e.g. within the range of 20-25% vol/vol.

Preferably, the cleaning composition comprises wax in an amount of 1-20% vol/vol, such as within the range of 2-19% vol/vol, e.g. within the range of 3- 18% vol/vol, such as within the range of 4-17% vol/vol; such as within the range of 5-16% vol/vol, e.g. within the range of 6-15% vol/vol, such as within the range of 7-14% vol/vol, e.g. within the range of 8-13% vol/vol, such as within the range of 9-12% vol/vol, e.g. within the range of 10-11 % vol/vol. The surfactant

The surfactant has been found to be important for the incorporation of the organic acid into the wax. A relatively large amount (at least 9 times the volume amount of surfactant compared to the amount of organic acid) was found to be necessary;

In one or more embodiments, the surfactant is selected from the group consisting of cationic surfactants, anionic surfactants, non-ionic surfactants, and mixtures thereof. Preferred anionic surfactants include an alkylcarboxylate, a polyalkoxycar- boxylate, an N-acylsarcosinate, a linear alkylbenzenesulfonate (LAS), an alpha-olefin sulfonate (AOS), a dialkylsulfosuccinate, an alcohol sulfate, and an ethoxyiated alcohol sulfate. Combinations of two or more of the aforementioned anionic surfactants are also useful the compositions of the present invention. Typical alkylcarboxylates include sodium, potassium or ammonium salts of C9-C21 fatty or rosin acids, such as la uric acid, palmitic acid, stearic acid, coconut fatty acids, hydrogenated coconut fatty acids, oleic acid, and the like.

Typical polyalkoxycarboxylates include alkoxylated alcohols, which have been end-capped with chloroacetate or acrylic acid. Polyalkoxycarboxylates are produced by reaction of ethylene oxide, propylene oxide, or mixtures thereof, with an alcohol, to produce an alkoxylated alcohol having about 2 to about 50 moles of oxyalkylene groups per mole of alcohol, followed by reaction of the free hydroxyl end group of the alkoxylate with chloroacetate or acrylate.

Typical N-acylsarcosinates are amidocarboxylates produced by the reaction of a fatty acid or rosin acid chloride with sodium sarcosinate. Commercial examples include sodium N-cocoylsarcosinate, sodium N-laurylsarcosinate, sodium N-oleoylsarcosinate and the like.

Typical commercial linear alkylbenzenesulfonates (LAS) include alkali metal or ammonium salts of alkylbenzenesulfonic acids, wherein the alkyl sub- stituent is a linear C9-C13 alkyl group such as sodium dodecylbenzene sulfonate (SDS).

Typical alpha-olefin sulfonates (AOS) are the products of sulfonation of alpha-olefins with sulfur trioxide and air, followed by neutralization of the intermediate sultones. Typical commercial examples include sulfonated Cioto Ci4 alpha-olefin, generally neutralized with an alkali metal hydroxide, an alkaline earth hydroxide, or an ammonium hydroxide.

Typical dialkylsulfosuccinates are alkali metal or ammonium salts of C5-C18 diesters of sulfosuccinic acid, such as sodium diamylsulfosuccinate, sodium dioctylsulfosuccinate, sodium di-(2-ethylhexyl)sulfosuccinate and the like. Typical commercial alcohol sulfates include alkali metal, alkaline earth metal or ammonium salts of sulfate esters of C ₈ -Ci2 alcohols such as sodium laurylsulfate, sodium 2-ethylhexylsulfate, lauryl triethanolammonium sulfate, sodium octylsulfate and the like. Typical ethoxylated alcohol sulfates are alkali metal or ammonium salts of sulfate esters of Ca-Cia alcohols ethoxylated with about 10 to about 40 weight percent of ethylene oxide, based on the weight of alcohol.

Preferred cationic surfactants include an amine, an aliphatic or rosin amine ethoxylate, an amidoamine, and a quaternary ammonium salt. Amphoteric surfactants that exhibit cationic properties below a pH of about 7 are also suitable for the present purposes, and are included herein under the term "cationic surfactant". Examples of such amphoteric surfactants are cocami- dopropyl betaine, carboxyalkyi imidazolines, and the like. Combinations of two or more of the aforementioned cationic surfactants can also be utilized in the compositions of the present invention.

Typical amine cationic surfactants include amines derived from fatty acids and rosins such as hydrogenated tallow amine, stearyl amine, lauryl amine, and the like, which are typically commercially available as acetate, oleate or naphthalenate salts. Other useful amine cationic surfactants include N-al- kyltrimethyleneamines having the general formula

wherein R ^* is an alkyl group derived from natural oils such as coconut, tallow and soybean oils and the like; 2-alkylimidazolines, such as 2-hep- tadecylimidazoline, 2-heptadeceny!imidazoline and the like! and 1-amino- ethyl-2-alkyl imidazolines. Typical commercially available aliphatic and rosin amine ethoxylate cationic surfactants include C ₆ -C ₂ o alkyl amines and rosin amines that have been ethoxylated with about 2 to about 50 moles of ethylene oxide per mole of amine, such as cocoamine, soyamine or stearylamine ethoxylated with 2 to 15 moles of ethylene oxide per mole of amine. Typical amidoamine cationic surfactants include condensation products of fatty carboxylic acids with di- and polyamines, such as condensates of diethylenetriamine with stearic, oleic, coconut, or tall oil fatty acids, and the like. Typical quaternary amine cationic surfactants include dialkyldimethyl- ammonium salts, such as dicocodimethylammonium chloride, distearyldi- methylammonium chloride, and the like; alkylbenzyldimethylammonium chlorides such as cocobenzyldimethylammonium chloride, tallowben- zyldimethylammonium chloride, stearylbenzyldimethylammonium chloride and the like; and alkyltrimethylammonium salts such as cetyltrimethyl- ammonium chloride, myristyltrimethylammonium bromide and the like; wherein the above alkyl groups are derived from fatty amines and rosin amines.

Particularly preferred cationic surfactants include fatty amines and rosin amines such as hydrogenated tallow amine, rosin amine ethoxylates, such as N,N-bis(2-hydroxyethyl)cocamine, N,N-bis(2-hydroxyethyl)soyamine; and salts thereof. Preferred salts are the acetates.

Preferred nonionic surfactants useful in the present invention include an alcohol alkoxylate, a polyol ester of a fatty acid, a polyoxyethylene ester of a fatty acid, a fatty acid amide, a polyoxyethylene fatty acid amide, a polyalkylene oxide block copolymer, an ethoxylated alkyl mercaptan, an ethoxylated anhydrosorbitol ester, and an alkyl polyglycoside. Also suitable are amine oxides prepared by hydrogen peroxide oxidation of tertiary aliphatic amines such as cetyldimethylamine oxide, stearyldimethylamine oxide, tallow-bis-(2-hydroxyethyl)amine oxide, stearyl-bis(2- hydroxyethyl)amine oxide, and the like. Combinations of two or more of the aforementioned nonionic surfactants are also useful in the compositions of the present invention . Typical alcohol alkoxylates include ethoxylated Ce-Cie linear and branched alcohols, ethoxylated with about 2 to about 80 moles of ethylene oxide, such as ethoxylated lauryl alcohol, ethoxylated stearyl alcohol, and ethoxylated mixtures of C ₆ -Ci ₈ alcohols, and alkoxylated natural alcohols such as ethoxylated propoxylated pine oil, ethoxylated soya sterol, and the like.

Typical polyol esters of fatty acids include saturated fatty acid mono- glycerides, such as glycerol monolaurate, glycerol monococo ester, glycerol monotallow ester, glycerol monostearate, and the like; saturated fatty acid diglycerides, such as glycerol distearate, glycerol dilaurate and the like; unsaturated fatty acid monoglycerides, such as glycerol monooleate, glycerol monoricinoleate, and the like; unsaturated fatty acid diglycerides, such as glycerol dioleate, glycerol dilinoleate, and the like; glycol esters of fatty acids, such as propylene glycol monostearate, ethylene glycol monostearate, ethylene glycol monolaurate, diethylene glycol monooleate, diethylene glycol monostearate, and the like; and anhydrosorbitol fatty acid esters, such as mono, di and tri esters of 1 ,4-sorbitan with fatty acids such as stearic acid, palmitic acid and oleic acid.

Typical polyoxyethylene esters of fatty acids are polyethylene glycol mono- and di-esters of fatty acids comprising a polyethylene glycol portion having from about 5 to about 30 ethyleneoxy units, esterified at one or both ends with fatty acids such as stearic acid, lauric acid, oleic acid, and mixed fatty acids derived from natural oils such as coconut oil, castor oil, tall oil, and the like. Typical fatty acid amides include diethanolamine fatty acid condensates such as coco diethanolamide, lauric diethanolamide, tall oil diethanolamide, and the like, and monoalkanolamine fatty acid condensates such as coco monoethanolamide, lauric monoethanolamide, stearic monoi- sopropanolamide, oleic monopropanolamide, and the like. Typical polyoxyethylene fatty acid amides are ethoxylated mono and dial- kanolamides having from about 2 to about 50 ethylene oxide groups, including ethoxylated lauric monoisopropanolamide, ethoxylated stearic diethanolamide, ethoxylated myristic monoethanolamide, ethoxylated oleic diethanolamide, and the like.

Typical polyalkylene oxide block copolymers include copolymers of ethylene oxide and propylene oxide initiated by ethylene glycol, propylene glycol, trimethylol propane, and the like, and have either linear or branched structures, depending on whether the initiator has two or three hydroxyl groups, respectively.

Typical ethoxylated alkyl mercaptans, include linear or branched alkyl mercapatans such as dodecylmercaptan, ethoxylated with 2 to 10 moles of ethylene oxide per mole of mercaptan.

Typical ethoxylated anhydrosorbitol esters are mono, di and tri esters of 1 ,4-sorbitan with fatty acids such as stearic acid, palmitic acid and oleic acid that have been ethoxylated with about 4 to about 20 moles of ethylene oxide per mole of anhydrosorbitol ester.

Typical alkyl polyglycosides are glycosides (acetals) of C ^' e-Cao alcohols with a monosaccharide such as glucose, fructose, lactose, mannose, xylose and the like or a polysaccharide or oligosaccharide such as isomaltose, maltose, cellobiose, mellobiose, maltotriose and the like.

Particularly preferred nonionic emulsifiers include fatty acid alkanolamides such as coconut diethanolamide, soya diethanolamide, and the like, and mixtures thereof. In one or more embodiments, the cleaning composition comprises a surfactant in an amount of 5-50% vol/vol, such as within the range of 6-45% vol/vol, e.g. within the range of 7-40% vol/vol, such as within the range of 8- 35% vol/vol, such as within the range of 9-30% vol/vol, e.g. within the range of 10-25% vol/vol, such as within the range of 12-23% vol/vol, e.g. within the range of 14-21 % vol/vol, such as within the range of 16-19% vol/vol.

In one or more embodiments, the cleaning composition comprises a non- ionic surfactant in an amount of 5-50% vol/vol, such as within the range of 6-45% vol/vol, e.g. within the range of 7-40% vol/vol, such as within the range of 8-35% vol/vol, such as within the range of 9-30% vol/vol, e.g. within the range of 10-25% vol/vol, such as within the range of 12-23% vol/vol, e.g. within the range of 14-21% vol/vol, such as within the range of 16-19% vol/vol. In one or more embodiments, the cleaning composition comprises a cationic surfactant in an amount of 5-50% vol/vol, such as within the range of 6-45% vol/vol, e.g. within the range of 7-40% vol/vol, such as within the range of 8-35% vol/vol, such as within the range of 9-30% vol/vol, e.g. within the range of 10-25% vol/vol, such as within the range of 12-23% vol/vol, e.g. within the range of 14-21% vol/vol, such as within the range of

16-19% vol/vol.

In one or more embodiments, the cleaning composition comprises a anionic surfactant in an amount of 5-50% vol/vol, such as within the range of 6-45% vol/vol, e.g. within the range of 7-40% vol/vol, such as within the range of 8- 35% vol/vol, such as within the range of 9-30% vol/vol, e.g. within the range of 10-25% vol/vol, such as within the range of 12-23% vol/vol, e.g. within the range of 14-21 % vol/vol, such as within the range of 16-19% vol/vol.

In one or more embodiments, the volume ratio between the organic acid and the surfactant is within the range of 1:9-1 :100, e.g. within the range of 1:10-1 :90, such as within the range of 1 :11-1 :85, e.g. within the range of

1 :12-1 :80, such as within the range of 1:13-1 :75, e.g. within the range of 1 :14-1 :70, such as within the range of 1:15-1 :65, e.g. within the range of 1 :20-1 :60, such as ithin the range of 1 :25-1 :55, e.g. within the range of 1 :30-1 :50, such as within the range of 1 :35-45, preferably within the range of 1 :9-1 :20.

Optimal components

In one or more embodiments, the cleaning composition comprises a UV absorber.

Examples of UV absorbers are benzotriazoles, benzophenones, and polymeric UV absorbers having a UV chromophore attached to a polymer backbone. In one or more embodiments, the cleaning composition comprises:

- organic acid in an amount of 0.5%-5% vol/vol;

- wax in an amount of 0.5-50% vol/vol;

- surfactant in an amount of 5-50% vol/vol; and

- solvent, preferably water, in an amount of 10-96% vol/vol;

wherein the volume ratio between the organic acid and the wax is within the range of 1 :1-1 :20.

In one or more embodiments, the cleaning composition comprises:

- organic acid in an amount of 1.75%-5% vol/vol;

- wax in an amount of 1.75-50% vol/vol;

- surfactant in an amount of 10-50% vol/vol; and

- solvent, preferably water, in an amount of 10-96% vol/vol;

wherein the volume ratio between the organic acid and the wax is within the range of 1 :1-1 :20.

It should be noted that embodiments and features described in the context of one of the aspects of the present invention also apply to the other aspects of the invention.

The invention will now be described in further details in the following non- limiting examples. Examples

The main object of this study was to test if the colonization of microorganisms on an offshore wind turbine could be retarded by treatment with a cleaning composition according to the present invention,

A series of tests were conducted with varying concentrations of wax and organic acids, as well as ratios between wax and organic acid. An exemplary cleaning composition is made by mixing 10% vol/vol nonionic surfactant (e.g. CAS number: 69011-36-5), 2.5% vol/vol cationic surfactant (e.g. CAS number: 863679-20-3), 4% vol/vol carnauba wax, 1.3% vol/vol glacial acetic acid, and 82.2% vol/vol water. Surfactants and wax are first mixed with about half of the water. Secondly, the glacial acetic acid is diluted in the remaining water, and the two solutions are then subsequently mixed. All components are easily commercially available.

When using organic acid in an amount of at least 0.5% vol/vol, surfactant in an amount of at least 9 times the amount of acid (1 :9 ratio or more), and where the volume ratio between the organic acid and the wax was within the range of 1 :1-1 :15, it was possible to retard the colonization of microorganisms on an offshore wind turbine with at least 30 months (testing still ongoing). Hence, the cleaning frequency of e.g. an offshore wind turbine can be extended from 12 months to at least 30 months,

The best results were obtained when using organic acid in an amount of at least 0.75-3% vol/vol, preferably 1.75-3% vol/vol, surfactant in an amount of at least 9 times the amount of acid (1 :9 ratio or more), and where the volume ratio between the organic acid and the wax was within the range of 1 :1-1 :5.