WO2022045916A1

WO2022045916A1 - Nanocomposite coatings to protect underwater and coastal infrastructure objects from biofouling

Info

Publication number: WO2022045916A1
Application number: PCT/RU2020/000451
Authority: WO
Inventors: Георгий Иванович ЛАЗОРЕНКО; Антон Сергеевич КАСПРЖИЦКИЙ
Original assignee: Общество С Ограниченной Ответственностью "Научно-Производственное Объединение "Минералика"
Priority date: 2020-08-25
Filing date: 2020-08-25
Publication date: 2022-03-03

Abstract

The invention relates to anti-fouling coatings intended to protect underwater and coastal infrastructure objects from biofouling, destruction and/or corrosion. Described is a bioactive polymer composition of a bioresorbable film coating with increased duration of effective coating action and a stable service life, in which composition a polymer of biogenic origin, chitosan, is used as the base and nanoparticles of Ag and/or ZnO are used as safe, environmentally nontoxic biocides which prior to inclusion into the biopolymer matrix are first precipitated onto the exterior surface and interior cavities of mineral nanotubes of halloysite which have been activated in a weak alkaline solution in order to ensure that the nanoparticles are evenly distributed in the biopolymer matrix, changes in their release are controlled, and the physical and mechanical properties of the coating are improved. The advantage of the coating is its environmental safety, biocompatibility, biodegradability, acceptable strength, expanded and increased ability to inhibit growth activity of microorganisms, and ability to not lose its properties during use and to retain them for a lengthy period.

Description

NANOCOMPOSITE COATINGS FOR THE PROTECTION OF UNDERWATER AND COASTAL INFRASTRUCTURE OBJECTS FROM BIOFOULING

Technical field

The invention relates to compositions for creating environmentally friendly anti-fouling film coatings designed to protect ships (ship hulls, ship devices, equipment and mechanisms) and underwater and coastal infrastructure (drilling rigs, water and oil and gas pipelines, port facilities, power plants, communication systems, navigation equipment and other engineering structures, products and structures) from biofouling, degradation and corrosion in the aquatic environment, and can be used in shipbuilding, as well as hydraulic engineering, transport and pipeline construction.

Prior Art

Marine and freshwater biofouling, caused by the accumulation of micro- and macroorganisms on underwater artificial surfaces, is a global problem affecting many sectors of the economy, including fishing, water transport, and hydrocarbon production [1–3]. Microbiological damage to underwater and coastal infrastructure causes significant damage to it and increases the risk of operating industrial and transport facilities. In conditions of changing environmental conditions, adaptation of aquatic microorganisms to new conditions, as well as the development of their resistance, this problem becomes even more acute.

The growth of colonies of microorganisms on surfaces of various morphologies is a global problem affecting many areas of human activity. In particular, at the enterprises of the fishery complex, biofouling leads to an approximately 20% increase in the cost of maintaining equipment for the reproduction of aquaculture [4]. According to estimates [5], fouling of ship hulls by marine organisms, contributing to an increase in hydrodynamic resistance, leads to an increase in fuel consumption by 41%. This leads to additional fuel consumption, estimated at about 300 million tons [6]. At present, the losses of the global economy associated with biofouling have already approached the mark of 150 billion dollars per year [7]. Fouling is also closely related to the development of corrosion of materials, which leads to their degradation and destruction of structures, greatly increasing the rate and degree of damage to marine equipment [8,9]. According to some estimates, biocorrosion and related damage amount to 30-50 billion dollars a year [10].

The most common and accessible methods of protection against biofouling and biocorrosion are currently paintwork materials (LKM) containing biocidal and anticorrosive additives. The composition of most antifouling LCMs includes copper-containing compounds [11], less often - compounds of tin, lead, arsenic [12], the use of which is based on the gradual erosion of the coating and the release of toxic biocides. In this case, depending on the mechanism of release of the active substance, existing solutions can be implemented either through contact leaching coatings (with an insoluble matrix) or through controlled depletion polymer coatings (with a soluble matrix) [11, 13].

An example of such solutions is an anti-fouling composition containing a copper-based biocide in an amount of less than 2 wt.% (in particular, copper (I) oxide, copper (I) thiocyanate, copper (I) sulfate or copper pyrithione), the basis of which is 20-100 wt.% film-forming polymer having an acrylic backbone (W02005075582 [14]).

A multilayer combined coating is known, consisting of a primer with anti-corrosion properties based on epoxy resin with targeted additives (bottom coating), antifouling enamel with an insoluble matrix based on a vinyl polymer modified with epoxy resin and containing copper oxide as a biocide (second coating), sparingly soluble or instant self-polishing paint based on rosin, in combination with polytetrafluoroethylene, containing a biocide in the form of copper compounds (third top coat) (RU2478114 C1 [15]).

Known anti-fouling and anti-corrosion coating, including 6.0-39.0 wt.% copper-containing biocide (spent copper-chromium-barium catalyst for the hydrogenation of synthetic fatty acids into higher fatty alcohols), 14.4-21.7 wt.% film-forming base (perchlorovinyl resin mixed with rosin and (or ) with pentaphthalic varnish) and the rest is a solvent (a mixture of solvent-naphtha and butyl acetate in a ratio of 1: 4 in the following ratio of components) (RU 96111452 A. [16]).

Similar coating systems are also described in W02004037933A1 ([17]), using copper oxide (CuO) from 22 to 75 wt.% and/or zinc pyrithione from 0.05 to 20 wt.%, resin from 5 to 20 wt.%, solvent from 3 to 30 wt.%, polyhexamethyleneguanidine salt from 0.05 to 20 wt.% and pigment from 1 to 50 wt.%, as well as in Chinese patent CN 101074331 B [18], describing a composite coating against biological fouling and corrosion in sea water , consisting of a ceramic oxide powder - 80-95 wt.% and 5-20 wt.% biocidal component - Cu, CuO OR CigO.

Patent RU 2114142 C1 [19] proposes an antifouling coating composition for application containing rosin, paraffin, and a biocide, which is used as arsenic sulfides obtained by sulfiding arsenic wastes from the processing of polymetallic ores, or arsenic trisulphide Arss(1). A significant drawback of the known biocides of antifouling coatings based on metal compounds (copper, lead, tin, mercury, etc.) and organometallic complexes is their toxicity to aquatic organisms. The ability of these compounds to bioaccumulate adversely affects the survival, growth, and reproduction of fish, crustaceans, invertebrates, and algae [20]. In [21], it was found that the effect of copper on the embryos of the sea urchin Paracentrotus lividus leads to disturbances in the differentiation of the bones of the skeleton and intestines of their larvae. After 96 hours of exposure, copper reduced the survival of red sea bream (Pagrus major) by 50% at a low concentration of 84.4 µg/L [22]. Copper can kill 50% of various crustacean populations after only 48 hours of exposure. The average lethal dose for the crabs Carcinus maenas is 109 mg/l, for the shrimp Crapdop shapdop - 29.5 mg/l, for the lobster larvae Homarus gammarus - 0.3 mg/l [23]. All this leads to the destabilization of marine ecosystems and very acutely poses the problem of the ecological situation in the waters of ports and areas of active human activity in the oceans.

At the same time, despite the high toxicity of heavy metal compounds for numerous aquatic communities, some algae exhibit a high degree of tolerance towards them and can easily attach to the surface treated with a coating containing metal-containing biocides [24]. This indicates a decrease in their effectiveness in some cases. In addition, this group of antifouling coatings are characterized by relatively high cost and low durability due to the uneven rate of biocide leaching from the coating.

These restrictions on the use of metal-based biocides have accelerated the development of non-toxic anti-fouling coatings.

The creation of new non-biocidal, non-biofouling surfaces is carried out in the following areas: preventing the attachment of polluting organisms to surfaces (fouling resistance of coatings); reduced adhesion between aquatic organisms and material surfaces (facilitated removal of contaminants); targeted destruction of polluting organisms (limitation of coating fouling) [25]. Existing non-biocidal coatings range from very hard, allowing for tough cleaning of contaminating organisms, to coatings with low energy surface properties that are easy to clean (self-cleaning). Self-cleaning coatings are based on materials with reduced adhesion between contaminants and the surface, resulting in easy removal of biofouling by simple mechanical cleaning or hydrodynamic stress during navigation [26,27]. Currently, the binders most used for non-biocidal coatings are poly(dimethylsiloxanes) (PDMS) and fluoropolymers (FP). Known coating composition based on vulcanized at room temperature a,w-dihydroxyesterified siloxane elastomers with different macromolecular chain lengths, containing oils, fillers (reinforcing silica and non-reinforcing carbonate), a hydrocarbon solvent for viscosity control, a hardener (in particular, tetraethoxysilane, methyl-tri - ethoxysilane or ethoxy-oligosiloxane) and a curing reaction catalyst (organometallic tetrafunctional compounds) (W02008074102A1 [28]).

Known composition for the preparation of coatings against biofouling based on polysiloxane, including a curing agent (vinyl triisopropeneoxysilane), multi-walled carbon nanotubes from 0.05 to 1 May. %, catalyst from 2 to 10 wt.%, consisting of a halogenated, fluorinated or chlorinated organic acid (US20120328554A1 [29]).

The invention EP1981659B1 [30] describes a non-toxic antifouling coating in the form of a microstructured and elastic surface, the microstructure of which contains a regular or random textured pattern with a height difference in the range of 40-450 µm, made of polydimethylsiloxane and silicone rubber.

However, the shortcomings of these binders do not allow to fully compensate for the absence of biocidal components in them. Thus, diatom biofilms formed are difficult to clean on these polymeric surfaces even at a high speed of 30 knots [31]. Polydimethylsiloxane is also susceptible to mechanical damage and has low adhesion to the substrate [32, 33]. In addition, leaching substances released by silicones during their fouling have a pronounced toxicological effect when interacting with enzymes involved in the curing of biological binders for crustaceans and affect the embryonic development of sea urchins and fish [34]. Thus, these coating materials not only do not inhibit biofouling, but also have side effects in the form of toxic decomposition products, which necessitates the search for environmentally friendly materials for antifouling coatings.

The solution to the above broad class of problems can be approaches based on the use of completely environmentally friendly materials that provide long-term and effective protection against biological fouling and destruction of engineering infrastructure in the aquatic environment.

One of the technical solutions closest to the claimed invention, based on this approach, is an environmentally friendly coating against marine biofouling, described in patent CN102010639B [35], consisting of a film-forming polymer, which is a modified organosilicon acrylic resin, a silane coupling agent and polyamide in as a hardener containing nanoparticles of silver (Ad), zinc oxide (ZnO) and pyrithione complexes (zinc, silver and copper) as biocidal agents.

The advantage of this solution is that the modified silicone acrylic resin has a low surface energy, making it difficult for microorganisms to attach to the treated surface. In turn, nanoparticles of silver, zinc oxide and pyrithione-metal compounds have a bacteriostatic and bactericidal effect, additionally preventing the adhesion of marine microorganisms to the treated surface.

However, this method of protection has serious limitations. First of all, this is that, despite the positioning by the authors of the invention CN102010639B [35] of the proposed coating as environmentally friendly, which is ensured by the replacement of traditional ecotoxic biocides with safe ZnO and nano-silver, this composition still involves the inclusion of copper pyrithione, the toxicity of which has been identified in relation to a number of marine organisms, including red pagra (Pagrus major) [22], shrimp Heptacarpus futilirostris [22], Artemia franciscana [36] and Artemia salina [37], algae Skeletonema costatum [38].

Another problem of this solution is that the direct introduction of Ad and ZnO nanoparticles into the polymer matrix does not ensure their uniform distribution in it due to the agglomeration of nanoparticles, which is due to the van der Waals and electrostatic interaction between them. Agglomeration of nanoparticles is the main obstacle to their use in such coatings, since it adversely affects their biological activity and does not provide effective and stable long-term protection against biofouling.

Another problem with this anti-fouling system is that although the low surface energy of the coating prevents the build-up of aquatic organisms, this protection mechanism requires relatively high vessel speeds to ensure the removal of contaminants.

Thus, despite the large number of different approaches, the problem of creating new non-biocidal non-biofouling coatings is still unresolved.

Disclosure of invention

The technical objective of the invention is to improve the efficiency of protection of underwater and coastal infrastructure from corrosion, degradation and/or biofouling, as well as the creation of an antifouling coating composition using environmentally friendly biocides that are effective for fouling suppression, but not toxic to marine and freshwater ecosystems, which helps to reduce anthropogenic impact on aquatic ecosystems and improve ecological situation in the water areas of ports and areas of active human activity in the oceans.

The technical results achieved by the proposed technical solution are:

- in the creation of a bioactive polymer composition of an environmentally friendly, biocompatible, bioresorbable film coating for the protection of underwater and coastal infrastructure in marine and freshwater reservoirs, with increased strength, duration of the effective action of the coating and a stable service life, which has a high ability to inhibit the growth activity of microorganisms, suitable for protection of various surfaces,

- in the development of a method for obtaining such a composition, as well as

- in developing a method for using such a composition in order to protect underwater and coastal infrastructure.

The task and the technical result are achieved by developing a polymer-based composition for protecting underwater and coastal infrastructure from biofouling, degradation and/or corrosion, containing biocidal additives and including the following components:

- as a polymer base - chitosan in an amount of 1.0-4.0 wt.% by weight of the entire composition, dissolved in a slightly acidic solution of an organic acid,

- as a biocidal additive - nanoparticles of silver (Ad) and / or zinc oxide (ZnO), deposited on the outer surface and internal cavities of halloysite mineral nanotubes (HNT), pre-treated with a 0.1-1.0 M alkali solution, the content of the biocidal additive in the composition is 1.0-10.0 wt.% in relation to the weight of the dry sample of chitosan,

- a weakly acidic solution of an organic acid used to dissolve chitosan, - the rest.

In some embodiments of the invention, the weakly acid solution of the organic acid is a 0.1-5.0% solution of a monobasic carboxylic acid.

In particular embodiments of the invention, the composition further comprises at least one pigment and/or at least one rheology regulator and/or at least one stabilizer and/or at least one structurant.

The task and the technical result are also achieved by implementing the method for obtaining the specified composition, which includes the following steps:

- processing of halloysite mineral nanotubes (HNT) with 0.1-1.0 M alkali solution; - deposition of nanoparticles Ad and/or ZnO on the outer surface and internal cavities of the GNT, and the processes of deposition of nanoparticles Ad and ZnO nanoparticles on the outer surface and internal cavities of the GNT are carried out separately from each other;

- dissolution of chitosan in a slightly acidic solution of an organic acid;

- adding Ad and/or ZnO nanoparticles deposited on GNT to the chitosan solution and their subsequent ultrasonic dispersion.

In some embodiments, the alkali is NaOH, KOH, LiOH, Ca(OH)g, or Ba(OH)g.

In some embodiments of the invention, the treatment of the GNT with a 0.1-1.0 M alkali solution is carried out to ensure an increase in the specific surface area and specific pore volume of the GNT by at least 5%.

In some embodiments of the invention, after the stage of GNT treatment with a 0.1-1.0 M alkali solution, the nanotubes are separated from the solution, washed with water to remove a possible alkali residue, and dried to constant weight at a temperature not exceeding 100 °C.

In some embodiments of the invention, the deposition of Ad nanoparticles on the outer surface and internal cavities of HNT is carried out by the method of liquid-phase chemical reduction in solutions, in which the precursor of silver nanoparticles is silver perchlorate, silver tetrafluoroborate or silver nitrate, and the reducing agent is sodium borohydride, glucose, ascorbic acid, tannin, formalin or hydrazine. In some particular embodiments of the invention, at the stage after adding the precursor of nanoparticles Ad and water, but before adding the reducing agent, the suspension is treated with ultrasound for at least 30 minutes, and the suspension is stirred on a magnetic stirrer for at least 24 hours, after which the resulting suspension placed in a vacuum chamber, where at least 3 cycles of evacuation of air from the vacuum chamber - filling of air to atmospheric pressure are carried out

In some embodiments of the invention, the deposition of Ad nanoparticles on the outer surface and internal cavities of HNT is carried out by thermal treatment of halloysite nanotubes saturated in an aqueous solution with silver ions, in which silver nitrate or silver acetate is used as a precursor of silver nanoparticles. In some embodiments of the invention, the deposition of ZnO nanoparticles on the outer surface and internal cavities of the GNT is carried out by thermal treatment of halloysite nanotubes saturated in an aqueous solution with zinc ions, in which zinc nitrate is used as a precursor of ZnO nanoparticles. In some particular embodiments of the invention, at the stage after the addition of the precursor and water, but before the heat treatment, the suspension is treated with ultrasound for at least 30 minutes, and the suspension is stirred on a magnetic stirrer for at least 24 hours, after which the resulting suspension is placed into a vacuum a chamber where at least 3 cycles of pumping air out of the vacuum chamber - filling air to atmospheric pressure are carried out.

In some embodiments of the invention, the deposition of ZnO nanoparticles on the outer surface and internal cavities of the GNT is carried out by the method of liquid-phase chemical reduction in solutions, in which the precursor of ZnO nanoparticles is zinc nitrate hexahydrate, and the reducing agent is sodium hydroxide. In some particular embodiments of the invention, at the stage after adding the precursor of ZnO nanoparticles and water, but before adding the reducing agent, the suspension is treated with ultrasound for at least 30 minutes, and the suspension is stirred on a magnetic stirrer for at least 24 hours, after which the resulting suspension placed in a vacuum chamber, where they carry out at least 3 cycles of pumping air from the vacuum chamber - filling air to atmospheric pressure.

In some embodiments of the invention, after the deposition of Ad and/or ZnO nanoparticles on the outer surface and internal cavities of the GNT, the resulting complexes are separated from the solution, washed with water to pH 6.5–7.5, dried to constant weight at a temperature of no more than 100 °C, and crushed. to the state of powder.

In some embodiments of the invention, at the stage of adding Ad and/or ZnO nanoparticles deposited on HNT to the chitosan solution, at least one pigment and/or at least one rheological properties regulator and/or at least one stabilizer and/or at least one structurant.

In some embodiments, the weakly acidic organic acid solution is a 0.1-5.0% carboxylic acid solution.

The task and the technical result are also achieved when implementing a method for protecting underwater and coastal infrastructure from biofouling, destruction and/or corrosion, which includes applying the specified composition to the surface to be protected, followed by keeping the solution on it until a film structure is reached.

In some embodiments of the invention, additional processing of the applied coating is carried out by washing with a 0.1 M alkali solution and drying at a temperature of 5-40 °C.

In some particular embodiments of the invention, the alkali is NaOH.

Detailed description of the invention

In the proposed compositions for the protection of underwater and coastal infrastructure from biofouling, degradation and / or corrosion, a polysaccharide of biogenic origin is used as the basis of a polymer film coating. - chitosan, and Ad and/or ZnO nanoparticles are used as safe non-ecotoxic biocides, which, before being included in the biopolymer matrix, are pre-deposited on the outer surface and internal cavities of alkali-activated halloysite mineral nanotubes (HNT) in order to ensure a uniform distribution of nanoparticles in the biopolymer matrix, controlling the dynamics of their release, ensuring the improvement of the physical and mechanical properties of the coating.

The use of biopolymers existing/created in living organisms has the prerequisites to become the basis for a highly effective and environmentally friendly antifouling coating due to their biocompatibility, antibacterial properties, low toxicity, environmental safety and relatively low cost. Many marine and freshwater organisms are resistant to colonization by other species. Their natural defenses involve a variety of mechanisms that inhibit sedimentation, secreted bioactive molecules, desquamated surface biolayers, mechanisms for biofilm formation, and release of hydrolytic enzymes. This opens up possibilities for using these natural mechanisms as the basis for "biomimetic" or "bioindustrialized" coatings.

The prerequisites for using chitosan, obtained from crustacean shell chitin, as the polymer matrix of the antifouling coating described in the present invention are that it has pronounced antibacterial and antifungal properties, as well as the absence of resistance to it in microorganisms. The cationic nature of chitosan determines its electrostatic interaction with the negatively charged components of the cell wall of microorganisms [39]. Chitosan and its derivatives have a high anticorrosion activity due to the presence of amine and hydroxyl groups in its structure [40, 41]. In addition, biogenicity, lack of toxicity, natural metabolic biodegradability, and biocompatibility for humans and the environment [42] make it potentially attractive to use chitosan and its derivatives as a “green” material for protective coatings.

The combination of the unique properties of chitosan with the valuable qualities of Ad and ZnO nanoparticles is the basis of the present invention, which involves the use of the positive properties of both: both the biopolymer base of the film coating and the biocidal nanoparticles included in it.

Ag nanoparticles, as the most reactive form of silver, exhibit high antibacterial activity against a wide range of bacterial and fungal species, including antibiotic-resistant strains [43]. They are low-toxic, thermostable and have a developed specific surface area. Inorganic zinc oxide nanoparticles are distinguished by such properties as low cytotoxicity, thermal stability, biocompatibility, and antimicrobial activity [44]. Among metal nanoparticles, ZnO occupies a dominant place in terms of safety and is certified as GRAS (Generally Recognized as Safe / generally accepted as safe) by the US Food and Drug Administration (FDA).

However, as noted above, the direct introduction of Ad and ZnO nanoparticles into the polymer matrix does not ensure their uniform distribution in it due to the agglomeration of nanoparticles, which is due to the van der Waals and electrostatic interactions between them. The agglomeration of nanoparticles is the main obstacle for their application in polymer-based coatings, which needs to be addressed.

Along with this, another problem of creating an environmentally friendly and effective antifouling coating in the context of the described invention is the low mechanical strength and structural stability of chitosan, which limits its use in "pure form" for protective coatings.

The solution of these problems in the present invention is provided by the use of the clay mineral halloysite, which is capable of being dispersed in liquid media to a nanoscale level, which acts as a nanocarrier for the deposition of biocidal nanoparticles used, as well as a reinforcing nanofiller that ensures the formation of a branched three-dimensional biopolymer-reinforced structure with improved physical and mechanical properties.

Halloysite is a natural aluminosilicate mineral representing multilayer nanotubes with an outer diameter of about 30–190 nm, an inner diameter of 10–100 nm, and a length of 0.7–30 μm [45]. The composition of halloysite nanotubes (HNTs) is similar to the clay minerals kaolinite, dickite, or nakrite with the chemical formula Al2Si2O5(OH) ₄ nH2O, where n = 0 and 2, which corresponds to the dehydrated and hydrated forms [45]. Halloysite, like many other clays, is widespread in the rocks of the sedimentary cover of the earth's crust. It is non-toxic to living organisms, which was confirmed in recent in vitro and in vivo experiments [46, 47], and does not pollute the environment, due to which, as well as its structural features, GNT seems to be a promising and cheaper alternative to synthetic analogues (in particular, , carbon nanotubes). In addition, halloysite nanotubes are characterized by a large specific surface area, high surface reactivity, and high mechanical strength.

Given the above features, according to the present invention, GNT are used to reduce the agglomeration of Ad and ZnO nanoparticles, which is ensured by their preliminary deposition on the outer surface and internal cavities of the GNT. This approach allows not only to ensure a uniform distribution nanoparticles of biocides on the coverage area, but also to increase the local concentration of biocides at the interface, bringing them closer to the cell membrane to improve the inhibition of microbial growth, as well as reduce the rapid release of nanoparticles Ad and ZnO. And due to the presence of a large number of hydroxyl and amino groups in chitosan, its strong binding to the surface oxygen functional groups of GNT is ensured, contributing to an increase in the mechanical strength of the nanocomposite film coating. Thus, preliminary deposition of Ad and ZnO nanoparticles on HNT provides not only better compatibility of biocide nanoparticles with the biopolymer matrix and the mechanical properties of the nanocomposite film coating, but also an increase in the biological activity of the antifouling coating composition.

To obtain a composition according to the invention, prior to the deposition of Ad and ZnO nanoparticles on HNT, preliminary alkaline treatment (activation) of halloysite nanotubes is carried out in order to increase the specific surface area and specific pore volume, as well as the reactivity of the mineral surface. In this case, the treatment is carried out with a relatively mild effect of alkali (preferably, but not limited to, 0.1-1.0 M solution of NaOH, KOH, LiOH, Ca(OH) ₂ , Ba(OH) ₂ ) in order to limit significant structural changes in halloysite , since exposure to a concentrated alkali solution can degrade the mechanical properties of the GNT due to the thinning of the walls. In preferred embodiments of the invention, the treatment of the GNT with an alkali solution is carried out to ensure an increase in the specific surface area and specific pore volume of the GNT by at least 5%. This process can be controlled by analytical methods (for example, transmission electron microscopy, scanning electron microscopy, X-ray diffraction, infrared spectroscopy) by recording structural and morphological signs of silica dissolution and an increase in the density of hydroxyl groups on the GNT surface. The amount of alkaline solution is chosen so as to ensure the processing of the entire mass of HNT, for example, effective processing can be achieved with a ratio of HNT and alkali from 1:10 to 1:30, but is not limited to this. For the purpose of more uniform mixing and activation of the processing process, during the processing, exposure to ultrasound for at least 30 minutes to homogenize the suspension and subsequent constant mixing at room temperature for no more than 24 hours can be carried out.

In some preferred embodiments of the invention, after the stage of processing halloysite mineral nanotubes with an alkali solution, they are separated (by filtration or centrifugation) from the solution, washed with water to remove a possible alkali residue, dried to constant weight at a temperature of not more than 100 ° C and, if necessary, crushed . Synthesis and deposition (loading) of Ad and ZnO nanoparticles on the outer surface and inner cavities of halloysite mineral nanotubes can be carried out by any known methods [48–50]. More preferable are methods that provide the most efficient deposition of Ad and ZnO nanoparticles on GNT. For example, in the case of Ad nanoparticles, the method of liquid-phase chemical reduction in solutions can be used, which consists in preparing a solution of an organic silver salt (in particular, silver perchlorate (AdSIO silver tetrafluoroborate (AdVB)) or silver nitrate (AdMO3), which are sources of silver ions, with subsequent addition of a strong reducing agent, which can be used, for example, but not limited to, sodium borohydride, glucose, ascorbic acid, tannin, formalin or hydrazine. in aqueous solutions of activated GNTs by reduction of silver ions with the help of reducing agents.Synthesis and precipitation (loading) of silver nanoparticles can also be carried out by thermal treatment (calcination) of halloysite nanotubes saturated in an aqueous solution with silver ions.In this case, as a precursor, nanoparticles silver particles can be used, for example, silver nitrate or silver acetate. The calcination of the treated halloysite nanotubes is typically carried out at a temperature of about 400° C. for about 1 hour to decompose the silver ion sources used and form silver nanoparticles.

In the case of ZnO nanoparticles, their synthesis and deposition (loading) on GNT can also be implemented, for example, by chemical deposition in solutions or heat treatment (calcination). Chemical precipitation in solution in the presence of halloysite nanotubes can be implemented using, for example, zinc nitrate hexahydrate as a precursor of ZnO nanoparticles, and sodium hydroxide as a reducing agent. In the case of calcination, for the synthesis of ZnO nanoparticles, for example, zinc nitrate can be used. The calcination of the treated halloysite nanotubes is typically carried out at a temperature of about 400° C. for about 1 hour to decompose the zinc ion sources used and form ZnO nanoparticles.

In some preferred embodiments, in order to obtain the best volumetric distribution of silver and zinc oxide nanoparticles in the GNT, after adding the precursor and deionized water to the activated GNT, the suspension is sonicated to homogenize it and saturate it with Ag (ZnO) ions (for at least 30 minutes ), as well as stirring the suspension on a magnetic stirrer for at least 24 hours at room temperature. To load the internal cavities at the stage of dispersion in the presence of a precursor, air is removed from the cavities of the nanotubes with its replacement with a solution of the loaded active substance by vacuum. To do this, the suspension is placed in a vacuum chamber, where at least 3 cycles of pumping air from the vacuum chamber - filling air to atmospheric pressure are carried out.

The resulting HNT/Ad nanoparticles or rHT/ZnO nanoparticles complexes are separated (by filtration or centrifugation) from the solution, washed with water to pH 6.5–7.5, dried to constant weight at a temperature of no more than 100°C, and ground to a powder. The obtained powders containing GNT/Ad nanoparticles and GNT/ZnO nanoparticles complexes can be (but not necessarily) mixed to obtain further compositions containing both silver nanoparticles and zinc oxide nanoparticles as biocidal additives. Mixing proportions can be absolutely any (0-100% in any direction) and are not limited in any way by the present invention.

To obtain the final composition (the so-called molding solution), chitosan is dissolved (in preferred embodiments of the invention, chitosan has a molecular weight of 10-2000 kDa) in a slightly acidic solution of organic acid (pH 4-6), with the addition and subsequent dispersion of precipitated (loaded) on halloysite nanotubes of Ad and/or ZnO nanoparticles until the aggregates of these particles are eliminated. In some embodiments of the invention, a slightly acidic solution of an organic acid is a 0.1-5.0% solution of a carboxylic acid (for example, acetic, lactic, citric, formic.

The concentration of the components in the final composition is chosen so that chitosan is 1-4 wt.% of the composition, and the content of the biocidal additive in the composition is 1.0-10.0 wt.% relative to the weight of the dry sample of chitosan.

The resulting composition is applied to the protected surface (substrate), followed by keeping the solution on the substrate until a film structure is achieved.

After applying the composition to the substrate, the resulting coating can be further processed by washing with a 0.1 M alkali solution and drying at a temperature of 5-40 °C. This procedure is not mandatory.

Additionally, the compositions for the protection of underwater and coastal infrastructure according to the invention may contain one or more pigments (such as, for example, natural or synthetic pigments) and/or additives, such as one or more agents for adjusting rheological properties (for example, polyethylene oxide, polyvinylpyrrolidone) , plasticizers (eg, glycerol, polyethylene glycol), stabilizers (eg, mannitol, sorbitol), structurants (eg, aldehydes), and other additives that impart specific properties to the composition as a whole and are well known to those skilled in the art. Such additives are introduced at the stage of preparation of the molding solution in the amount necessary to impart the required properties to the composition. Brief description of the drawings

The invention is illustrated by drawings, where in Fig. 1 shows a flow diagram of the procedure for preparing the described nanocomposite coating for the protection of underwater and coastal infrastructure from biofouling, degradation and/or corrosion.

Definitions and terms

Unless otherwise specified, all technical and scientific terms used in this application have the same meaning as understood by those skilled in the art. References to techniques used in the description of this invention refer to well-known methods, including modifications of these methods and replacing them with equivalent methods known to those skilled in the art.

In the description of the present invention, the terms "comprises" and "comprising" are interpreted to mean "includes, among other things." These terms are not intended to be construed as "consisting only of".

"Halloysite"("mineral halloysite nanotubes", "halloysite nanotubes", "GNT") is a natural clay mineral with a generalized chemical formula AI ₂ Si ₂ O5 (OH) ₄ nH ₂ O (where n = 0 and 2), having a tubular , spheroid or lamellar morphology of particles, formed mainly in the process of chemical weathering or hydrolysis of rocks, as well as by hydrothermal means. Halloysite of any deposit having a tubular particle morphology is suitable for carrying out the invention.

Chitosan is a linear polysaccharide obtained by deacetylation of chitin. There are no special requirements for chitosan used to carry out the invention. In some preferred embodiments of the invention, the molecular weight of chitosan is 10-2000 kDa.

"Nanocomposite" - a multicomponent composite material consisting of 2 or more separated phases, in which at least one of the phases has an average size of individual elements (particles, crystallites, fibers, plates, etc.) less than 100 nm at least in one dimension.

"Precursor" - a substance involved in the reaction leading to the formation of the target substance. In the context of the present invention, the precursor for the synthesis of silver nanoparticles can be silver nitrate or an organic silver salt, for the synthesis of zinc oxide nanoparticles - zinc nitrate or zinc nitrate hexahydrate, but not limited to them.

The possibility of an objective manifestation of the technical result when using the invention is confirmed by reliable data given in the examples, containing information of an experimental nature, obtained in the process of conducting research according to the methods adopted in this field.

It should be understood that the examples given in the application materials are not limiting and are provided only to illustrate the present invention.

Example 1

To prepare activated HNT, a sample of natural halloysite with a fraction of less than 2 μm is mixed with 0.2 M NaOH at a phase ratio of HNT and alkali from 1:20 and sonicated for at least 30 minutes to homogenize the suspension, followed by constant stirring at room temperature for not less than 5 hours, but not more than 24 hours. The solution is separated by filtration from the solid residue, which is washed with water to remove a possible NaOH residue (up to pH 7) and dried to constant weight at a temperature not exceeding 100 °C and crushed to a powder.

Silver nanoparticles were deposited on GNT by chemical reduction with sodium borohydride (NaBH) from an aqueous solution based on silver nitrate (AgN03). Activated HNTs (25 g) in a 5% solution of silver nitrate (AgNO3) in deionized water (500 ml) were sonicated for 30 minutes to homogenize the suspension and saturate with silver ions with stirring on a magnetic stirrer for 24 hours at room temperature. To load the internal cavities of the nanotubes, the vessel with the resulting suspension was placed in a vacuum chamber, where 3 cycles of evacuation of air from the vacuum chamber - filling of air to atmospheric pressure were carried out. After adding the reducing agent (100 ml of 0.1 M NaBH ₄ solution). stirring was continued for 30 minutes. After that, halloysite nanotubes with precipitated (loaded) Ad nanoparticles were separated from the solution by centrifugation at 7000 rpm and washed in deionized water until neutral pH. Then they were dried at 100°C for 5 h and ground to a powder state.

The film coating was prepared as follows. An air-dry sample of chitosan (20 g) was added to a 2% aqueous solution of acetic acid (1000 ml) and stirred for 24 h at room temperature. Further, the solution was filtered from impurities and clots. Then, a dispersion of Ad nanoparticles deposited on activated GNTs (5 wt.% with respect to solid chitosan) was introduced into the resulting solution, dispersed in ultrasound for 30 min, and stirred on a magnetic stirrer for 12 hours at room temperature.

The resulting molding solution was applied to the substrate and kept until the film structure was reached for 5 days at a temperature of 25°C and a relative air humidity of 50%. After drying, the coating was washed with neutralizing reagent, which was 0.1 M NaOH solution, and re-dried at 25 °C in air to obtain the resulting coating.

Example 2

It repeats the procedure of Example 1, except that ultrafine ZnO is used as biocidal nanoparticles, the deposition (loading) of which in GNT is carried out as follows.

Activated HNT (25 g) was added to a 0.1 M solution of zinc nitrate 6-aqueous (n(N03)2-6H2O) in deionized water (500 ml). The resulting suspension was sonicated for 30 minutes for homogenization and stirred on a magnetic stirrer for 8 hours at 60°C to saturate the HNT with Zn ^{2+ ions} . To load the internal cavities of the nanotubes, the vessel with the resulting suspension was placed in a vacuum chamber, where 3 cycles of evacuation-filling of air to atmospheric pressure were carried out. Chemical precipitation was carried out by adding 4 M NaOH solution. After adding the precipitant, stirring was continued for 30 minutes. After that, halloysite nanotubes with precipitated (loaded) ZnO nanoparticles were separated from the solution by centrifugation at 7000 rpm and washed in deionized water until neutral pH. Then they were dried at 100°C for 5 h and ground in a porcelain mortar to a powder state.

The film coating was prepared in the same manner as described in Example 1.

Example 3

The test results obtained in accordance with examples 1 and 2 samples of dried thin films with a thickness of 200-150 μm are shown in table 1. To illustrate the effects of adding Ad and ZnO nanoparticles deposited on the outer surface and internal cavities of the GNT on the properties of the initial chitosan, a control sample was prepared according to the method , set forth in examples 1 and 2, without the addition of HNT with nanoparticles Ad and ZnO.

The mechanical properties (tensile strength and Young's modulus) of the prepared films were measured using a universal testing machine according to ASTM E111-97 Standard Test Method for Young's Modulus, Tangent Modulus, and Chord Modulus.

The ability of nanocomposite films to inhibit the formation of a bacterial biofilm was studied on the example of gram-positive and gram-negative microorganisms - cultures of Staphylococcus aureus Staphylococcus aureus and Escherichia coli. Microorganisms were sown by "lawn seeding" on a nutrient agar medium, on which the tested films were placed. The exposure time was 24 hours. The bactericidal activity was controlled by the size of the zone diameter. delaying the growth of cultures of microorganisms seeded with "lawn" at the location of the test sample of the film.

Table 1.

Thus, preliminary deposition (loading) of Ad and ZnO nanoparticles on HNT provides not only better compatibility of biocide nanoparticles with the biopolymer matrix and improved mechanical properties of the nanocomposite film coating, but also an increase in the ability of the antifouling coating composition to inhibit the growth activity of microorganisms.

Uniform distribution of HNT with nanoparticles of Ad and/or ZnO biocides provided by the invention over the coverage area of the protected surface, increase in their local concentration at the interface, slowdown (up to complete absence) of the release of biocide nanoparticles loaded into HNT, in combination with the biocidal properties of the biopolymer base coating - chitosan makes it possible to achieve high biocidal activity of the composition according to the invention while maintaining the operational properties of the coating throughout the entire period of its use.

The combination of essential features of the proposed coating provides an increase in the effectiveness of protection of underwater and coastal infrastructure in the aquatic environment from corrosion and biofouling, as well as the protection of water resources from the negative environmental consequences of anthropogenic impact.

The advantage of the proposed antifouling nanocomposite coating is its environmental safety, biocompatibility, biodegradability, acceptable strength, extended and increased ability to inhibit the growth activity of microorganisms, the ability not to lose their properties during operation and retain them for a long period of time. The proposed nanocomposite coating is effective for protecting various surfaces, including, but not limited to, metal, polymer, concrete, wood surfaces.

While the invention has been described with reference to the disclosed embodiments, it should be apparent to those skilled in the art that the specific experiments described in detail are for the purpose of illustrating the present invention only and should not be construed as limiting the scope of the invention in any way. It should be clear that various modifications are possible without departing from the essence of the present invention.

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Claims

Claim

1. Polymer-based composition for protecting underwater and coastal infrastructure from biofouling, degradation and/or corrosion, containing biocidal additives and including the following components: as a polymer base - chitosan in an amount of 1.0-4.0 wt.% by weight of the composition, dissolved in weakly acid solution of organic acid, as a biocidal additive - nanoparticles of silver (Ad) and / or zinc oxide (ZnO), deposited on the outer surface and internal cavities of halloysite mineral nanotubes (HNT), pre-treated with 0.1 -1.0 M alkali solution , the content of the biocidal additive in the composition is 1.0-10.0 wt.% relative to the weight of the dry sample of chitosan, the weakly acidic solution of organic acid used to dissolve the chitosan is the rest.

2. Composition according to claim 1, in which a slightly acidic solution of an organic acid is a 0.1 -5.0% solution of a monobasic carboxylic acid.

3. The composition according to claim 1, further comprising at least one pigment and/or at least one rheology regulator and/or at least one stabilizer and/or at least one structurant.

4. A method for obtaining a composition according to any one of paragraphs 1-2, including the following steps:

- treatment of halloysite mineral nanotubes (HNT) with 0.1 -1.0 M alkali solution;

- deposition of Ad and/or ZnO nanoparticles on the outer surface and internal cavities of the HNT, and the process of deposition of the Ad nanoparticles on the outer surface and internal cavities of the HNT is carried out separately from the process of deposition of ZnO nanoparticles on the outer surface and internal cavities of the HNT;

- dissolution of chitosan in a slightly acidic solution of an organic acid;

5. The method according to claim 4, wherein the alkali is NaOH, KOH, LiOH, Ca(OH) ₂ or Ba(OH) ₂ .

6. The method according to claim 4, in which the treatment of the GNT with a 0.1 -1.0 M alkali solution is carried out to ensure an increase in the specific surface area and specific pore volume of the GNT by at least 5%.

7. The method according to claim 4, in which, after the stage of HNT treatment with a 0.1-1.0 M alkali solution, the nanotubes are separated from the solution, washed with water to remove a possible alkali residue, and dried to constant weight at a temperature not exceeding 100 °C.

8. The method according to claim 4, in which the deposition of nanoparticles Hell on the outer surface and internal cavities of the GNT is carried out by the method of liquid-phase chemical reduction in solutions, in which the precursor of silver nanoparticles is silver perchlorate, silver tetrafluoroborate or silver nitrate, and the reducing agent is sodium borohydride, glucose , ascorbic acid, tannin, formalin or hydrazine.

9. The method according to claim 4, in which the deposition of Ad nanoparticles on the outer surface and internal cavities of the HNT is carried out by thermal treatment of halloysite nanotubes saturated in an aqueous solution with silver ions, in which silver nitrate or silver acetate is used as a precursor of silver nanoparticles.

10. The method according to claim 4, in which the deposition of ZnO nanoparticles on the outer surface and internal cavities of the GNT is carried out by the method of liquid-phase chemical reduction in solutions, in which the precursor of ZnO nanoparticles is zinc nitrate hexahydrate, and the reducing agent is sodium hydroxide.

11. The method according to claim 4, in which the deposition of ZnO nanoparticles on the outer surface and internal cavities of the GNT is carried out by thermal treatment of halloysite nanotubes saturated in an aqueous solution with zinc ions, in which zinc nitrate is used as a precursor of ZnO nanoparticles.

12. The method according to any one of claims 8 or 10, in which, at the stage after adding the precursor of Ad or ZnO nanoparticles and water, but before adding the reducing agent, the suspension is treated with ultrasound for at least 30 minutes, and the suspension is stirred for magnetic stirrer for at least 24 hours, after which the resulting suspension is placed in a vacuum chamber, where at least 3 cycles of pumping air from the vacuum chamber-filling air to atmospheric pressure are carried out.

13. The method according to any one of claims 9 or 11, in which at the stage after adding the precursor and water, but before the heat treatment, the suspension is treated with ultrasound for at least 30 minutes, and the suspension is stirred on a magnetic stirrer in for at least 24 hours, after which the resulting suspension is placed in a vacuum chamber, where at least 3 cycles of pumping air from the vacuum chamber-filling air to atmospheric pressure are carried out.

14. The method according to claim 4, in which after the deposition of Ad and/or ZnO nanoparticles on the outer surface and internal cavities of the HNT, the resulting complexes are separated from the solution, washed with water to pH 6.5-7.5, dried to constant weight at a temperature not over 100 °C and crushed to a powder state.

15. The method according to claim 4, in which at the stage of adding Ad and/or ZnO nanoparticles deposited on HNT to the chitosan solution, at least one pigment and/or at least one rheological properties regulator and/or at least one stabilizer and/or at least one structurant.

16. The method according to claim 4, in which the weakly acidic solution of organic acid is a 0.1-5.0% solution of carboxylic acid.

17. A method for protecting underwater and coastal infrastructure from biofouling, degradation and / or corrosion, including applying the composition according to any of claims 1-3 to the surface to be protected, followed by keeping the solution on it until a film structure is reached.

18. The method according to claim 17, including additional processing of the applied coating by washing with a 0.1 M alkali solution and drying at a temperature of 5-40 ° C.

19. The method of claim 18 wherein the alkali is NaOH.