WO2008009067A1

WO2008009067A1 - Antifouling coating

Info

Publication number: WO2008009067A1
Application number: PCT/AU2007/001013
Authority: WO
Inventors: Peter David Steinberg; Timothy Charlton; Anisul Afsar
Original assignee: Newsouth Innovations Pty Limited
Priority date: 2006-07-20
Filing date: 2007-07-20
Publication date: 2008-01-24
Also published as: AU2007276712B2; AU2007276712A1

Abstract

Disclosed herein is a method for treating a surface to inhibit fouling of the surface. The method comprises the steps of forming a coating on the surface and exposing the coating to conditions whereby the surface topography of the coating changes to a surface topography that inhibits the fouling of the surface. Also disclosed are antifouling compositions.

Description

ANTIFOULING COATING

TECHNICAL FIELD

The present invention relates to methods for treating a surface to inhibit fouling of the surface, for example, by aquatic organisms. The invention also relates to antifouling and self-cleaning coating compositions.

BACKGROUND ART Many industries suffer from problems associated with the fouling of surfaces. For example, in the maritime industry, when artificial surfaces (such as ships' hulls, aquaculture cages or pens, wharf pilings, filters, cooling pipes, etc.) are exposed to seawater, they are rapidly colonised ("fouled") by marine organisms. Such fouling can result in substantial costs to the maritime industry, for example, because of loss of hydrodynamic efficiency of ships resulting in increased fuel costs, blockage of flow of water in pipes, a'ήd cόrros'άέJn. Similarly, in aquatic (freshwater) environments', fouling on boats, water pipes, wharves, and infrastructure generally is a major problem. Microbial fouling on the walls of buildings can also cause major damage to structures.

A common way of combating fouling is to coat surfaces with antifouling coatings such as paints that release a toxin or inhibitor which kills fouling organisms as they settle on the surface, or soon after. However, many of these coatings are very toxic and have undesirable environmental effects.

Another way of combating fouling is to coat surfaces with "non-stick" coatings based on ■silicone elastomers, which reduce the ability of'" fouling- organisms to initially stick to a surface and, if^' attached, prevent strong attachment. In the maritime industry, such coatings are primarily suited for ships or other surfaces which are exposed to fast flowing water, for example, vessels which spend relatively little time in port and operate at speeds of greater than 15 knots. These coatings are therefore not suitable for use in many contexts, for example, on stationary underwater structures, aquaculture, and most recreational and coastal commercial vessels.

DISCLOSURE OF THE INVENTION ,^• >^;

In a first aspect, the ^' present invention provides a method for treating a surface to inhibit fouling of the surface. The method comprises the steps of forming a coating on the surface and exposing the coating to conditions whereby the surface topography of the coating changes to a surface topography that inhibits the fouling of the surface.

In the context of the present invention, the term "fouling" refers to the attachment of biological organisms (e.g. aquatic organisms) or organic or inorganic materials (e.g. dirt or grease) to a surface.

The phrase "inhibit fouling of the surface", and the like, refers to inhibiting .the attachment of biological organisms or organic⁽*"br inorganic materials to the surface. This encompasses both 'inhibiting biological organisms or organic or inorganic materials from becoming attached to the surface, as well as inhibiting or reducing the adherence of any biological organisms or organic or inorganic materials that do become attached to the surface. By . inhibiting or reducing the adherence of biological organisms or organic or inorganic materials to the surface, any biological organisms or organic or inorganic materials attached to the surface are relatively easily removed (this is referred to as a foul release effect) .

In a second aspect, the present invention provides a method for treating a surface to inhibit fouling of the surface by aquatic organisms. The method comprises the step of forming a coating on the surface wherein the surface topography of the coating changes after immersion in water to a surface topography that inhibits the fouling of the surface by aquatic organisms .

In some embodiments of the method of the first or second aspect, the coating comprises a polymeric substance having two or more phases. In such embodiments, the change in surface topography may be caused by degradation of an exposed phase of the coating. .

For example, the coating may comprise a polymeric substance having an amorphous phase and a crystalline phase) . In such embodiments, the change in surface topography may be caused by the preferential degradation of the amorphous phase over the crystalline phase. The degradation may, for example, be caused by bacteria present in water to which the coating is exposed (e.g. immersed) .

In some embodiments, the polymeric substance is a macrocrystalline wax, for example, a paraffin wax. In some embodiments, the paraffin wax is a paraffin wax with a melting point within the range of about 48 °C to about 65⁰C.

In some embodiments, the coating comprises a mixture of polymeric substances, for example, a mixture of paraffin waxes or a mixture of paraffin wax(es) and a silicone oil.

In a third aspect, the present invention provides a method for treating a surface to inhibit fouling of the surface. The method comprises the steps of (a) forming a coating on the surface, the coating comprising a polymeric substance having two or more phases, and (b) treating the coating such that the coating is capable of inhibiting fouling of - A - the surface .

Typically, the surface is treated to inhibit fouling by aquatic organisms when the surface is submerged in water. However, in some embodiments, surfaces such as building walls, which are only occasionally wetted or which are merely moist, can also be treated.

In some embodiments, the treatment in step (b) comprises exposing the coating to conditions that change the surface topography of the coating to a surface topography that inhibits fouling of the surface (e.g. by aquatic organisms) .

In some embodiments, the polymeric substance has an amorphous phase and a crystalline phase. In such embodiments, step (b) may. comprise immersing the coated surface in water, wherein a change in the surface topography of the coating is caused by the preferential biodegradation of the amorphous phase over the crystalline phase. The biodegradation may, for example, be caused by bacteria in the water.

In a fourth aspect, the present invention . provides a method for inhibiting the fouling of a surface by aquatic organisms. The method comprises the step of forming a coating on the surface, the coating comprising a polymeric substance having an amorphous phase and a crystalline phase, wherein, after immersion in water, the surface of the coating changes to form a coating that inhibits fouling by aquatic organisms .^'•••

The methods of the present invention may be used to inhibit the fouling of submerged surfaces by marine organisms. The surface may, for example, be a surface of an underwater pylon, pipe or pen, or a submerged surface of a buoy or boat . Alternatively, the methods of the present invention may be used to inhibit the fouling of medical devices, heat exchanger systems or buildings, by biological, organic or inorganic foulants.

In a fifth aspect, the present invention provides an antifouling coating composition comprising a polymeric substance capable of forming two or more phases when the composition is applied to a surface to form a coating on the surface.

Typically, the polymeric substance is capable of forming an amorphous phase and a crystalline phase. When the antifouling coating composition comprising such a polymeric substance is applied to a surface to form a coating on the surface, the polymeric substance has an amorphous phase and a crystalline phase in the resultant coating. ^■ • • N ^' . ^•

The antifouling coating composition of the fifth aspect of the present invention may, for example, be used to form a coating on a surface in accordance with the method of the first, second, third or fourth aspect of the present invention.

In a sixth aspect, the present invention provides an article having a surface which has been coated by an antifouling coating composition of the fifth aspect of the present invention.

BRIEF DESCRIPTION OF THE FIGURES

Preferred embodiments of the present invention are described below, by way of example only, with reference to the following Figures, in which:

Figure 1 shows a graph depicting the results of experiments described in Example 1, the graph showing the percentage of the surface of various samples that was fouled (mean ± SE) after 2, 4 and 6 months immersion;

Figure 2 shows a graph depicting the results of experiments described in Example 1, the graph showing the percentage of the surface of the samples of Figure 1 that was fouled (mean ± SE) after 6 months immersion, both before and after washing the- surface with a waterjet;

Figure 3 shows a graph depicting the results of experiments described in Example 1, the graph showing the percentage of the surface of the samples of Figure 1 that was fouled (mean ± SE) after 12 months immersion, both before and after washing the surface with a waterjet;

Figure 4 shows a graph depicting the results of experiments described in Example 1 (at Port Stephens) , the graph showing the percentage of the surface of various samples that was fouled (mean ± SE) after 8 weeks immersion following washing of the surface with a waterjet;

Figure 5 shows a graph depicting the results of experiments described -in Example 1 (at ^' Kirribilli, Sydney Harbour) , the graph showing¹ the percentage of the surface of various samples that was fouled (mean ± SE) after 8 weeks immersion following washing of the surface with a waterjet ;

Figure 6 shows a graph depicting the results of experiments described in Example 2, the graph showing the percentage of the bryozoan larvae (Bugula neritina) that had settled on the surface of various samples after 24 hours ;

Figure 7 shows an image obtained from confocal scanning laser microscopy, which depicts the initial surface topography of a cross section of the paraffin wax sample described in Example 1;

Figure 8 shows an image obtained from confocal scanning laser microscopy, which depicts the surface topography of the paraffin wax sample of Figure 7 after 9 weeks immersion in seawater;

Figure 9 shows the spectra obtained from X-Ray Diffraction (glancing angle) analysis of a sample of paraffin wax which has not been exposed to seawater;

Figure 10 shows the, spectra obtained from X-Ray Diffraction (glancing angle) . analysis of a sample of paraffin wax following immersion in seawater for 8 weeks,-

Figure 11 shows the spectra obtained from X-Ray Diffraction (glancing angle) analysis of a sample of paraffin wax which has not been exposed to seawater;

Figure 12 shows the spectra obtained from X-Ray Diffraction (glancing angle) analysis of a sample of paraffin wax which has been exposed to seawater containing antibiotics; and

Figure 13 shows the spectra obtained from X-Ray Diffraction (glancing angle) analysis of a sample of paraffin wax which has which-has been exposed to seawater.

DETAILED DESCRIPTION OP THE INVENTION

As discussed above, the first aspect of the present invention provides a method for treating a surface to inhibit fouling of the surface. The method comprises the steps of forming a coating on the surface and exposing the coating to conditions that change the surface topography of the coating to a surface topography that inhibits the fouling of the surface. Once the coating is formed, .the coating is exposed to conditions such that the surface topography changes to a surface topography that inhibits fouling of the surface. The change in surface topography may be caused by any process that results in the surface having an appropriate topography. Typically, the process is a degradative process (e.g. in which the coating is degraded such that it has a surface topography that inhibits fouling of the surface) . The degradative process can be biological (e.g. biodegradation) , chemical (e.g. etching) or physical (e.g. erosion through currents and flow or wind) . The coating may, for example, be subjected to enzymatic degradation, photo-degradation, or chemical degradation to change the surface topography of the coating to a surface topography that inhibits fouling of the surface. Combinations of biological, chemical 'and 'physical- degradative processes can occur (e.g. where a physical process aids the process of biological or chemical degradation by removing the degradation products from the surface thereby exposing non-degraded material for subsequent biological or chemical degradation) . Typically, the surface topography that inhibits fouling is a surface topography having a roughness on a micro- and/or nano-scale, that is, a roughness at the microscale (i.e. between 1 and 1000 microns) and/or at the nanoscale (i.e. between 1 and 1000 nanometres) .

In some embodiments, the coating is exposed to conditions whereby the surface topography changes to a surface topography that inhibits fouling of the surface by exposing the coating to an artificial environment, or by a person applying a chemical (e.g. a solvent or enzyme) or biological organism to the coating. In other embodiments, the coating is exposed to ambient conditions (e.g. the atmosphere or immersion in an aquatic environment) whereby the surface topography changes to a surface topography that inhibits fouling of the surface.

The second aspect of the present invention provides a method for treating a surface, to inhibit fouling of the surface by aquatic organisms^:..v > The method comprises the step of forming a coating¹ on. the surface wherein the surface topography of the coating changes after immersion in water to a surface topography that inhibits the fouling of the surface by aquatic organisms.

These methods of the first and second aspects of the present invention advantageously achieve their antifouling properties by virtue of the surface topography of the coated surface changing after the coating is formed (e.g. after the surface has been immersed in water) . As the antifouling property is provided by the surface topography, it is not necessary to include toxins in the composition which may leach into the environment, which makes this method especially useful in applications where the surface is in close proxϋmiiiy^' to food, for example, in aquaculture. ■ ^{: ' :'}

The surface topography of the coating may be changed upon immersion in water via any mechanism which causes the surface topography to change to form a surface topography that inhibits the attachment of aquatic organisms to the surface (i.e. which inhibits fouling) . The change in surface topography need not be instantaneous upon immersion in water but, in some embodiments, may occur over a period of time. For example, the surface topography of the coating may change when exposed to environmental micro-organisms present in water which biodegrade the coating to change its surface topography.

The coating may, for "-example, ''comprise a mixture of phases (such as a crystalline and amorphous phase, as is discussed in detail below) or a mixture of different components, where the different phases or components differentially degrade (e.g. when immersed in water) such that the surface topography of the coating changes. For example, the surface topography of the coating may change when exposed to a solvent because of factors such as the different solubilities, reactivity or melting points of phases or components of the coating.

In the second aspect ',pf the _; present invention, the change in surface topography occurs. after immersion of the coating in water. Without wishing to be bound by theory, whilst the mechanism by which the change in surface topography upon immersion in water inhibits fouling has not yet been completely ascertained, the inventors consider that the antifouling property occurs because the coating is degraded upon immersion in the water (e.g. biodegraded by bacteria present in the water) such that the topography of the coating has a roughness on a number of scales, including a roughness on at least micro- and/or nano-scale.

A coating having a roughness on micro- and/or nano-scales provides an extremely uneven surface which deters aquatic organisms with a lar-g.e ^■■range * o£_\ sizes from attaching to the surface. Further, even should the organisms become attached to the surface, the roughness results in the attachment being weaker than would be the case on a smooth surface, and the organisms can therefore be relatively easily removed from the surface (e.g. by movement of the water past the surface or by other organisms) , thus providing a coated surface having both antifouling and foul release properties.

For example, a surface having a micro-scale roughness may deter a barnacle larva with a diameter of ~0.5 mm from binding to the surface, however, such a level of roughness is unlikely to deter algal spores with a diameter of -0.005 mm from binding to the surface. However, a nano- scale roughness overlaying a micro-scale roughness inhibits binding of both the barnacle larva and algal spores to the surface.

The inventors also note it is at least possible that, in embodiments where the coating is degraded by bacteria, the bacteria may persist on the surface of the coating and contribute to the antifouling effect (i.e. in addition to the surface roughness) by secreting chemical substances which inhibit the subsequent colonisation by aquatic organisms, or the bacteria may leave a residue on the surface which inhibits subsequent colonisation by aquatic organisms. Other factors, which the inventors note might contribute to the antifouling effect include changes in the wettability and hydrophobic!ty of the coating.

Typically, the coating comprises a polymeric substance having an amorphous phase and a crystalline phase, as described below. In such embodiments, the change in surface topography is typically caused by the preferential degradation (e.g. biodegradation) of the amorphous phase over the crystalline phase, resulting in a surface topography that has a roughness on both micro- and nano- scales.

The third aspect of the present invention provides a method for treating a surface¹ to inhibit fouling of the surface. The method comprises ■^' the steps of (a) forming a coating on the surface, the coating comprising a polymeric substance having two or more phases, and (b) treating the coating such that the coating is capable of inhibiting fouling of the surface.

In this aspect, the coating is treated in such a way that the physical or physicochemical properties of the • surface have an antifouling effect. Typically, the treatment in step (b) changes the surface topography of the coating to a surface topography that inhibits fouling of the surface, as discussed above. It is envisaged that the surface could be treated, for example, by enzymatic degradation, photo-degradation or chemical degradation to change the surface topography of the coating to a surface topography that inhibits fouling of the surface. However, the coated surface may alternatively, or in addition, be treated in other ways to provide an antifouling effect. For example, the surface may be treated by exposing the surface to bacteria which colonise the surface and act as a deterrent "living layer" against subsequent colonisation by aquatic organisms by secreting natural antifouling substances. The coated surface may also be treated in a manner whereby the wettability or hydrophobicity of the surface is changed in a way to inhibit fouling.

The method of the third aspect may be performed in order to treat the surface to inhibit fouling by aquatic organisms when the surface is* submerged in water. In such embodiments, the treatment -in step (b) typically changes the surface topography of the coating to a surface topography that inhibits fouling of the surface by aquatic organisms. In such cases, the treatment in step (b) may, for example, comprise immersing the coating in water, wherein the surface topography of the coating changes to a surface topography that inhibits fouling as referred to above in relation to ' the second. aspect of the present invention. However/ ^' step' (b) of the third aspect need not involve immersion in water, and it is envisaged that the surface could be treated, for example, by exposing the coated surface to enzymatic degradation prior to immersing the surface in water. As such, antifouling properties may be imparted to the surface prior to the surface ever making contact with water. For^' example, step (b) may comprise treating the coating to enzymatic degradation, photo-degradation, or chemical degradation to change the surface topography of the coating to a surface topography that inhibits fouling of the surface by aquatic organisms.

In some embodiments, the coating comprises a polymeric substance that has an amorphous phase and a crystalline phase. The resultant surface may inhibit fouling because the treatment in step (b) causes the surface topography to change because of the preferential degradation of the amorphous phase over the crystalline phase (or vice versa) . The amorphous and crystalline phases may differentially degrade because of differing biological, chemical (e.g. pH, solubility, reactivity) or physical (e.g. melting point) characteristics of the phases.

The rates of degradation may be affected by the phases of the polymeric substance (e .g. ^■ crystalline/amorphous/semi- crystalline) and arrangements '■ within each of these phases (e.g. type of crystal, structure) . ^• Typically, amorphous regions degrade at a faster irate than crystalline regions.

In preferred embodiments of this aspect of the invention, the treatment in step (b) involves immersing the surface in water such that bacteria in the water preferentially biodegrade the amorphous phase of the coating over the crystalline phase.

The polymeric substance is preferably a macrocrystalline wax such as a paraffin wax. However, there are many examples of polymeric substances which have amorphous and crystalline phases and that could be used as a coating for use in the methods of the present invention.

Examples of biodegradable, polymeric substances which have amorphous and crystalline 'phases are listed below: - polyhydroxyalkanoates (PHAs) , such as PHA co-polymers and blends, and polyhydroxy alkanoates;

- poly-hydroxy butyrate and epichlorhydrin elastomer blends; - poly (lactic acid) and related polymers, such as poly- lactic acid and polyglycolic acid co-polymers, poly (L-lactide) -TiO2 composites, blends of poly(lactic acid) and poly (ethylene glycol), poly lactic acid and microcrystalline cellulose (MCC) , multiblock copolymers of L-lactide and trimethylene carbonate, blends of polylactide and poly (methyl methacrylate) , poly( (L) -lactide-co-RS-beta-malic acid) , poly (ethylene oxide) /poly (L-lactic acid) (PELA) multiblock, and poly (ether-ester-urethane) s; - poly (caprolactone) , such as multiblock copolyesters prepared from epsilon-caprolactone, L-lactide, and trimethylene carbonate, poly (pentadecalactone-co-oxo- crown ether) , multiblock copolymer consisting of poly (propylene fumarate) and poly (epsilon- caprolactone), and poly (epsilon-caprolactone) ;

- poly (terephthalate/alkylene and succinate/adipate)

, ' ^' , ' ' ' and related copolyesters, such as poly (butylene succinate) (PBS) and its copolyesters, poly (butylene adipate) , poly (alkylene succinate) blends, poly (butylene terephthalate/succinate/adipate) , poly (butylene terephthalate) /poly (butylene adipate- co-terephthalate) , poly (butylene adipate-co-butylene terephthalate) ,, poly (butylene adipate) , poly (ethylene succinate) , and poly (butylene succinate) ; - block-copolyesterurethanes, such as poly (ester urethanes) based on levoglucosan monoacetate; 2

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- chitosan/chitin, such as poly (epsilon-caprolactone) with alpha-chitin and chitosan, and chitosan/ synthetic polymer;

- polyvinyl alcohol, such as poly (vinyl butyral) / poly(vinyl alcohol) /nylonδ (N6) , poly (L-lactide) and poly (vinyl alcohol) blends; and

- cellulose, such as cellulose diacetate-graft-poly (L- lactide) s .

It is expected that any of these polymers could be used in the methods of the present . invention.

In embodiments where the polymeric substance is one or more paraffin waxes, the coating may further comprise silicone oil. Experiments conducted by the inventors have shown that the addition of silicone oil can enhance the foul release properties of the resultant coating.

The fourth aspect of the present invention provides a method for inhibiting the fouling of a surface by aquatic organisms. The method comprises the step of forming a coating on the surface, the coating comprising a polymeric substance having an amorphous phase and a crystalline phase, wherein, after immersion in water, the surface of the coating changes to form a coating that inhibits fouling by aquatic organisms.' •

Whilst this invention¹ is primarily intended for use in marine applications, it will be appreciated that fouling also occurs in other aquatic systems and the present invention may therefore also be used in such systems. For example, the methods of the present invention could be used to inhibit fouling in freshwater systems (e.g. lakes or rivers) or to coat medical devices to prevent the build-up of harmful bacteria, for example, on catheters or in dialysis machines. The methods of the invention could also be used, for example, to coat air-conditioners or cooling heat exchangers in power plants to prevent the build-up of biofilm etc.

Examples of marine applications of the invention include on ships' hulls, aguaculture cages, nets or pens, buoys, wharf pilings, underwater pylons, pipes, filters, etc.

Examples of non-marine applications include in medical devices (e.g. catheters, stents, dialysis machines), heat exchanger systems in cooling plants, water piping in general, cooling towers and other water storage systems, freshwater boats, pilings, wharves and other infrastructure or on buildings exposed to conditions where fouling is common.

The present invention also provides an antifouling coating composition. The antifouling coating composition comprises a polymeric substance capable of forming two or more phases (e.g. an amorphous phase and a crystalline phase) when the composition is applied to a surface to form a coating on the surface. When the antifouling coating is applied to a surface to form a coating on the surface, the polymeric substance has two or more phases in the resultant coating. For example, the coating may have crystalline/amorphous/semi-crystalline phases .

The polymeric substance in the antifouling composition may be any of the polymeric substances described above. The antifouling composition may additionally comprise other components which facilitate the application of the polymeric substance (s) to^;the surface. For example, the composition may also include an adherent or preservant.

The invention also provides an article, such as any of those described above, which has been coated by an antifouling coating composition of the invention. Coating the surface

In the methods of the present invention, a coating is formed on the surface. Typically, the entire surface is coated, however, in some circumstances it may only be necessary to coat a portion of the surface to achieve an acceptable level of antifouling. For marine applications, the coating may be applied to a surface or part of the surface intended to be submerged in water.

The coating may be formed on the surface by methods known in the art for applying coating compositions to a surface to form a coating on the surface. The coating may be formed by applying a coating composition of the present invention to the surface. In some embodiments, the coating composition is sprayed or painted onto the surface to form a coating on the surface. Alternatively, the coating composition could be applied to the surface by dip coating.

The methods of the present invention may also involve additional steps, for example, in some embodiments the coating may be heated prior to application to the surface (as is the case for the embodiments described below where the coating comprises paraffin waxes) .

When the coating comprises a polymeric substance, the coating composition may further comprise additional compounds, for example, an adherent to increase the adhesion of the coating to the surface, or a preserving compound to prolong the life of the coating.

The coating may be applied directly to the surface on its own, or as a top coat on, for example, a sealant coat or an anticorrosion coat.^' i r .

Preferred embodiments of the present invention will now be described below. In these embodiments, a coating is formed on a surface by applying to the surface a composition comprising a paraffin wax, or a mixture of paraffin waxes, and the antifouling properties occur because of the changed surface topography of the coating following immersion of the coated surface in water.

Any paraffin wax that biodegrades when placed in water which contains a normal contingent of aquatic/marine bacteria may be used. The inventors have found that coatings comprising fully refined paraffin waxes have excellent antifouling characteristics, are well suited as coatings for a wide range of surfaces, persist on surfaces in typical aquatic environments, are very economical, and are not toxic or otherwise environmentally unsound. Fully refined paraffin waxes are, for example, used in candle making and in food applications such as sealants for the top of jams and other preserves.

Paraffin waxes are composed of straight-chain saturated hydrocarbons (n-alkanes) . Fully refined paraffin waxes include a mixture of n-alkanes and the melting point ranges of the fully refined paraffin waxes indicates which n-alkanes are present'' in the wax. Although n-alkanes make-up the bulk of fully! refined paraffin waxes, fully refined paraffin waxes may also contain other hydrocarbons such as branched chain, cyclic and polyaromatic hydrocarbons or other compounds usually found in paraffinic fractions from crude petroleum. These impurities may contribute to the antifoul effect as they can mediate crystallization (i.e. the rate of crystallisation and the size of crystals formed) of the n- alkanes .

Suitable paraffin waxes typically have melting points between about 48⁰C and about 70⁰C, preferably between about 55⁰C and about 65⁰C. If the melting point is lower than 48⁰C, then coatings formed from the waxes are not durable, and may not set properly upon application to a surface. If the melting point is higher than 70⁰C, then the wax may be more difficult for bacteria to biodegrade. Preferably, the paraffin wax has a melting point of about 60⁰C, for example, a melting point range of about 58 to about 62⁰C.

In preferred embodiments, the composition comprises one or more paraffin waxes (eg. a fully refined paraffin wax containing a range of n-alkanes) .

The antifouling coating may be^' formed on the surface by applying the paraffin wax' to the surface in a liquid (i.e. hot) form. As the wax cools to form a solid coating on the surface, two phases are formed; an amorphous phase and a crystalline phase. The amorphous phase forms preferentially on the exposed surface of the coating because the wax cools most rapidly at the surface. The inventors believe, however, that the wax cools more slowly underneath the surface and the wax molecules underneath the surface are able to become more ordered such that a more crystalline phase is formed.

Without wishing to be bound by theory, the inventors believe that, when such coating is exposed to water, the outer layer (i.e. the amorphous phase) of the coating is removed relatively quickly and easily by bacteria in the water, thereby exposing the crystalline phase. The crystalline phase, however, is either unaffected by bacterial action, or is more slowly degraded than the amorphous phase. The exposed surface of the crystalline phase present at the biodegraded surface consists of crystals having various shapes and sizes, and provides a surface topography with a roughness in both the micro- and nano-scales. For the reasons discussed above, this topography inhibits the fouling of the coated surface by a broad range of fouling organisms.

The inventors have also performed experiments which show that antifouling coatings comprising waxes prepared according to the methods of the present invention are effective for a considerable length of time (exceeding 1 year) . The inventors believe that even the crystalline phase of the waxes is biodegraded, albeit at a slower rate. Thus, the surface topography of the coating formed from waxes is continually changing, even after the rough crystalline phase has been exposed. As such, the roughness of the surface is maintained throughout the lifetime of the coating, and the roughness does not become overlaid by other components in the water over time, which would decrease the effectiveness of the coating as an antifoulant. ^{' '}}^■ ■^•, ^;- ■'^■.^'■' ■

In' some embodiments, the composition may comprise a mixture of a paraffin wax and silicone oil. The inventors have found that coating compositions comprising about 1% w/w silicone oil and a paraffin wax result in antifouling coatings with enhanced properties over coatings formed from only paraffin wax. The inventors postulate that the silicone oil may contribute to the surface roughness of the degraded coating, as well as providing a degree of hydrophobicity to the surface.

EXAMPLES

Examples of preferred embodiments of the invention in which the coating comprises ^■ a fully refined paraffin wax will now be described^'. It will be appreciated that these examples are merely illustrative of the present invention and are not intended to be limiting in any respect.

Example 1 - Preparation and antifouling activity of coatings comprising paraffin waxes

The effects of paraffin wax based antifouling coatings on initial settlement/colonisation by a number of fouling organisms were investigated in both the laboratory and the sea. Two invertebrate species (one barnacle, Balanus amphitrite and one, bryozoan, Bugula neritina) and one algal species (Polysiphonda sp. ) were chosen as representative test organisms for the laboratory fouling trials .

Antifouling waxes The antifouling properties of the fully refined paraffin waxes listed below were tested in the experiments described below. The paraffin waxes are distinguished by the range of melting points of the waxes and the nomenclature used to identify these waxes in the experiments described below is as follows:

(Pl) - Paraffin wax: MP 58-60⁰C

(P2) - Paraffin wax: MP 55-57°C

(P3) - Paraffin wax:-' ,MP '61-63,⁹C (P4) - Paraffin wax: <VMP 57-59'⁰C

(P5) - Paraffin wax: MP 56-58°C

(P6) - Paraffin wax: MP 60-62⁰C

(P7) - Paraffin wax: MP 68-71°C

(P8) - Paraffin wax: MP 52-54°C (P9) - Paraffin wax: MP 47-49°C

The antifouling activity of a number of non-paraffin waxes having similar melting points were also tested. The nomenclature used to identify these waxes in the experiments described below is as follows:

B(IO) - Beeswax: MP 64-66°C

M(Il) - Microcrystalline wax: MP 64-67°C

Pal (12) - Palm wax: MP 50-52⁰C- ; . , ^■ > ^•

Method for preparing sample surfaces

Wax disks (5.4 cm diameter) were prepared using plastic Petri dishes. The sides of the Petri dishes were cut down to a height of 1.8 mm and prior to addition of the wax they were placed on a heated metal tray or oven (ca. 80⁰C) to facilitate an even spread of the wax. The wax was melted and 12 ml was transferred to the Petri dish with a heated plastic syringe. This resulted in an even film of wax with a depth of about 2 mm in the Petri dish.

Field test sites The field trials were conducted in Sydney Harbour, at

Kirribilli (New South Wales, Australia) and Port Stephens (New South Wales, Australia) . Tidal action, water currents and wave energy were minimal at both sites.

At Kirribilli, the cages were suspended in the sea at a fixed depth (with the top of the cage 0.4 m underwater) . At Port Stephens, the trays were fixed to the seafloor.

Cages Cages were used for all trials at Kirribilli to protect any settled propagules from predator and grazers. The cages were approximately 90 x 75 x 30 cm³ in size and made from 2 cm² plastic mesh. A _.total of 30 wax disks were placed in randomly assigned positions within each cage. '

The Port Stephens trial used an enclosed oyster tray with the wax disks fixed to the underside of the tray tops. The wax surfaces were face down and immersed for other than the lowest tides.

Fouling assessment

Photos of each sample disk were taken using a digital camera (every fortnight for the field trial in Sydney Harbour and less frequently for the field trial at Port Stevens) . Fouling cover was measured as a proportion of the disk area (% fouling cover) . The percent of fouling cover on the disks was assessed by analysing the images W

- 23 - using the 'Image J' software (National Institutes of Health, USA) .

The relative adhesion strength of soft fouling organisms (slime, algae, bryozoans etc.) was measured by exposing the test disks to a waterjet (with a head pressure of about 50 kPa) .

Sample disks were prepared with each of the paraffin waxes P(I) to P (9), and the other waxes B(IO), M(Il) and

Pal (12) . A 5.4 cm disk of Perspex with no coating was also included in all of the experiments as a control sample (this is referred to as "Plastic" in the figures) .

The samples were immersed in the sea and the % fouling was measured at periodic intervals, as described above.

Figure 1 shows the proportion of three sample disks (the control sample and samples M(Il) and P(I)) which was covered after 2, 4 and 6 months immersion. As can clearly be seen, the paraffin wax coating has significantly less fouling than the control and the microcrystalline wax coating.

Figure 2 shows the same three samples after 6 months immersion, both before and after the surfaces were sprayed with a waterjet to remove any loosely bound foulants. Again, the paraffin wax coating has significantly less fouling than the control and the microcrystalline wax coating, both before and after the surfaces were sprayed with a waterjet. The results indicate that even when fouling organisms do colonise the surface of the paraffin wax coating, they are bound more weakly than when bound to a normal plastic surface or an alternate wax coating.

Figure 3 shows the same three samples after 12 months immersion, both before and after the surfaces were sprayed with a waterjet to remove any loosely bound foulants . Again, the paraffin wax coating has significantly less fouling than the control and microcrystalline wax coating. Further, even after 12 months, the foulants are more readily removed from the paraffin wax surfaces than for control and microcrystalline wax surfaces.

Figures 4 and 5 show the results of similar experiments using the other waxes referred to above (P(2) to PO)) following immersion for 8 weeks at Port Stephens (Figure 4) and Kirribilli (Figure 5) and after the surfaces were sprayed with a waterjet to remove any loosely bound foulants. As can clearly be seen, all of the paraffin wax coatings have significantly less fouling than the controls or the other wax coatings.

These experiments suggest that' not only are paraffin waxes excellent antifoulants for stationary objects, being resistant to initial fouling, they would also be effective for use an as antifoulant on moving objects, as any foulants which do colonise the surface are readily removed from the paraffin wax surface.

The other waxes, which are not macrocrystalline waxes, are clearly less effective at inhibiting antifouling than the paraffin waxes.

Additional experiments performed by the inventors (results not shown) in which the paraffin wax samples contained 1% silicone oil demonstrated that the presence of the silicone oil enhances the¹ foul release properties of the resultant coating. ^{' ■} •^■

Example 2 - Effect of antibiotics on antifouling activity The role that bacteria play in enhancing the antifouling activity of compositions comprising paraffin waxes was tested by immersing paraffin wax coatings in the seawater systems described below.

Seawater treatment involved immersion of samples for 4 or 8 weeks in flow or static conditions. Antibiotics were added to one of the static seawater treatments so bacteria would not be present in this system. The antifouling activity of surfaces treated in systems where the seawater contained an antibiotic was compared with the activity of surfaces in systems containing just seawater.

Samples in the form of Petri dishes coated with paraffin wax (P(I)) were immersed in the laboratory systems described below for 4 and 8 weeks. An uncoated control Petri dish (referred to as "Plastic" in Figure 6) was not immersed in the seawater.

Once removed from the system, the samples (i.e. the coated Petri dishes) were dried and later used for settlement inhibition bioassaysl 'These assays were conducted under static flow condition's 'by adding 15 - 25 bryozoan larvae

(Bugula neritina) in each¹ Petri dishes with 5ml of 0.2μm filtered sea water. After 24 hours the numbers and percentage of settled (metamorphosed) larvae was determined using a stereo microscope.

Replicates of the samples were exposed to one of the following kinds of seawater treatment:

(Flow) : Recirculating seawater: 8 L, replaced every ~2.7 minutes (flow rate ~50 ml/ second) ;

(Stat. -AB) : Static seawater: 8 L, replaced every 7 days ; and (Stat. +AB): Static filtered seawater (0.2 μm) plus antibiotics ■ (a'mpicillin, 300 ppm, polymixin B sulphate, 30 ppm, and gentamicin sulphate, 60 ppm) : 8 L, replaced every 7 days. A control experiment, in which the samples were not subjected to any seawater treatment, but were stored in air for 4 and 8 weeks, was also conducted. All treatments were aerated with filtered (0.2 μm) air.

The results are shown in Figure 6 and demonstrate that the presence of antibiotics in the seawater significantly reduces the antifouling properties of the paraffin wax. These results indicate that bacteria present in seawater plays a significant role in enhancing the antifouling property of the surface coating formed from paraffin wax.

These results also show that there appears to be little difference in the activity of .bacteria in degrading the paraffin wax under either flow or static conditions.

Example 3 - Characterisation of topography of a paraffin wax surface The surface topography of a paraffin wax coating P(I) was imaged by a Leica Inverted Confocal Microscope (magnified 63Ox) and analysed using Leica Confocal Software both before immersion in the sea ' and . after 9 weeks immersion.

The surface topography of a cross section of the non- immersed P(I) wax coating" and the surface topography of a cross section of the same wax coating after 9 weeks immersion is shown in Figures 7 and 8 respectively. As can clearly be seen, the surface topography of the paraffin wax coating that has been exposed to seawater is significantly rougher than that of the surface before immersion. These results demonstrate that the surface topography of coatings formed from paraffin waxes do change upon immersion in seawater and are consistent with the postulation that bacteria degrade the wax to expose the rough crystalline phase.

Figures 9 and 10 show the spectra obtained from X-Ray Diffraction (glancing angle) experiments conducted on nonaged P (6) paraffin wax (i.e. paraffin wax which has not been exposed to seawater) and aged paraffin wax (i.e. paraffin wax which has been exposed to seawater for 8 weeks in the laboratory seawater aquarium) , respectively.

Amorphous surfaces are known to attenuate x-ray intensity, and at small angles the degree of attenuation increases. The surfaces of the wax samples were therefore analysed by grazing incidence X-ray diffraction configured for 2θ scan. Intensity of the (Θ-2Θ) • beam in. the range (15-30 degrees, arc) was recorded for incident angles of 0.4, 0.5, 0.8 and 1.2 degrees (non-aged wax) and 0.2, 0.5 and 1.2 degrees (aged wax) . Penetration depth of the x-ray is estimated to^' be about 15 μm.

A low intensity, broad peak was detected in the spectrum shown in Figure 9 (non-aged wax) , which is characteristic of an amorphous phase. The intensity the peaks for the non-aged wax is also less than the peaks for the aged wax.

The greater signal intensity for the peaks in the spectrum shown in Figure 10 (aged wax) indicates a much greater proportion of crystalline phase paraffin at the surface than for the non-aged wax. '^■ Signal intensity is known to be proportional to crysta'llinity using this technique.

Referring now to^* Figures 11 to 13, these spectra show XRD data from three treatments; non-aged wax (Figure 11), aged wax treated with antibiotics (Figure 12, i.e. no bacteria present), and aged wax without antibiotics (Figure 13, i.e. bacteria may be present) . The crystalline signal from the later sample (i.e. Figure 13) is much stronger than either of the first two, which supports the hypothesis that aging removes the amorphous layer, and the presence or not of antibiotics implies that bacteria are responsible for aging the paraffin wax samples. In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as

"comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Claims

CLAIMS :

1. A method for treating.a surface to inhibit fouling of the surface, the method comprising the steps of forming a coating on the surface and exposing the coating to conditions whereby the surface topography of the coating changes to a surface topography that inhibits the fouling of the surface.

2. The method as claimed in claim 1, wherein the coating is exposed to conditions whereby a degradative process changes the surface topography of the coating to a surface topography that inhibits the fouling of the surface .

3. The method as claimed in claim 2, wherein the degradative process^1' is...a physical, chemical or biological process. ^1; '^■

4. A method for treating a surface to inhibit fouling of the surface by aquatic organisms, the method comprising the step of forming a coating on the surface wherein the surface topography of the coating changes after immersion in water to a surface topography that inhibits the fouling of the surface by aquatic organisms.

5. The method as claimed in any one of claims 1 to 4, wherein the coating comprises a polymeric substance having two or more phases .

6. The method as claimed in claim 5, wherein the change in surface topography is caused by degradation of an exposed phase of the coating.

7. The method as claimed in any one of claims 1 to 6, wherein the coating comprises a polymeric substance having an amorphous phase and a crystalline phase.

8. The method as claimed in claim 7, wherein the change in surface topography is caused by the preferential degradation of the amorphous phase over the crystalline phase.

9. The method as claimed in claim 8, wherein the degradation is caused by bacteria present in water to which the coating is exposed.

10. The method as claimed in any one of claims 5 to 9, wherein the polymeric substance is macrocrystalline wax.

11. The method as claimed in any one of claims 5 to 10, wherein the polymeric substance is a paraffin wax.

12. The method as claimed in claim 11, wherein the paraffin wax has a melting point within the range of about 48 "C to about 65⁰C.

13. The method as claimed in any one of claims 1 to 12, wherein the coating comprises a mixture of paraffin waxes.

14. The method as claimed in any one of claims 1 to 13, wherein the coating comprises a mixture of one or more paraffin wax(es) and a silicone oil.

15. A method for treating a surface to inhibit fouling of the surface, the method comprising the steps of:

(a) forming a coating on the surface, the coating comprising a polymeric substance having two or more phases, and

(b) treating the coating such that the coating is capable of inhibiting the fouling of the surface.

16. The method as claimed in claim 15, wherein the surface is treated to inhibit fouling by aquatic organisms when the surface is submerged in water.

17. The method as claimed in claim 15 or claim 16, wherein step (b) comprises exposing the coating to conditions that change the surface topography of the coating to a surface topography that inhibits fouling of the surface . .

18. The method as claimed in any one of claims 15 to 17, wherein the polymeric substance has an amorphous phase and a crystalline phase.

19. The method as claimed in claim 18, wherein step (b) comprises immersing the coated surface in water, and wherein a change in the surface topography of the coating is caused by the preferential biodegradation of the amorphous phase over the crystalline phase.

20. The method as claimed in claim 19, wherein the biodegradation is caused by bacteria in the water.

21. The method as claimed in any one of claims 15 to 20, wherein the polymeric substance is a macrocrystalline wax.

22. The method as claimed in any one of claims 15 to 21, wherein the coating comprises a mixture of paraffin waxes.

23. The method as claimed in any one of claims 15 to 21, wherein the coating comprises a mixture of one or more paraffin wax(es) and a silicon oil.

24. A method for inhibiting the fouling of a surface by aquatic organisms, the method comprising the step of forming a coating on the surface, the coating comprising a polymeric substance having an amorphous phase and a crystalline phase, wherein, after immersion in water, the surface of the coating changes to form a coating that inhibits fouling by aquatic organisms.

25. The method as claimed in any one of the preceding claims, when used for inhibiting the fouling of a submerged surface by marine organisms.

26. The method as claimed in any one of the preceding claims, wherein the surface is a surface of a pylon, pipe, pen, buoy, boat, medical device, heat exchanger system or building.

27. An antifouling coating composition comprising a polymeric substance capable of forming two or more phases when the composition is applied to a surface to form a coating on the surface.

28. The antifouling coating composition as claimed in claim 27, wherein the polymeric substance is capable of forming an amorphous phase and a crystalline phase .

29. The antifouling coating composition as claimed in claim 27 or 28, when used to form a coating on a surface in accordance with the method of any one of claims 1 to 26.

30. An article having a surface which has been coated by an antifouling coating composition of claim 27 or claim 28.