Copper-Free Environmentally Friendly Next-Generation Anti-Fouling Paints

Abstract

Biofouling—microorganisms, plants and various organisms that attach to submerged portions of vessels operating in marine environments and surfaces in contact with seawater—causes reduced speed and increased fuel consumption in these vessels. Additionally, the cleaning of biofouling and the time spent on it increase costs. Coatings applied to prevent biofouling pollute the environment due to their constituent compounds. This study presents results from work on the development of next-generation paint with copper-free antifouling properties for a sustainable environment.

Introduction

Unwanted accumulations created by microorganisms, plants and organisms on surfaces in contact with seawater are termed biofouling. These cause reduced speed in maritime vessels, greater fuel consumption, increased cleaning expenses and time, and environmental pollution. For years, work has been conducted on protecting the surfaces of vessels and structures remaining in marine environments against biofouling [1-5]. In ancient times, ship hulls were painted with lime for antifouling purposes, later with arsenic, mercury and pesticides. In the 1960s, the chemical industry developed the effective and low-cost organotin compound tributyltin (TBT). In the 1970s, the vast majority of ships navigating the seas were painted with TBT. Soon after, it became apparent that effective antifouling paints containing TBT posed an environmental problem. Environmental studies demonstrated that the organotin compound did not dissolve in the sea, accumulated on the seabed and on organisms living on it, killed marine life that attached to places other than ship hulls, and presumably entered the food chain.

Between 1970 and 1980, high levels of TBT observed in shellfish (oysters) off the French coast caused the closure of commercial shellfish farms in at least one region, and the issue was taken up by the International Maritime Organization (IMO), which began imposing bans on TBT-containing paints.

In 1997, Japan banned TBT production. In 2008, the IMO banned the use of TBT-containing paint worldwide. After TBT was banned globally, copper-based antifouling paints took its place. Copper paints demonstrated antifouling effectiveness because they exhibited performance similar to TBT and are the paints that dominate the market today. In copper antifouling paints, although copper flakes or powder is also used, the primary component is copper oxide. Cu2O dissolves in seawater, creating the reactions shown in Equations 1 and 2. Both reactions are reversible. Since dissolved oxygen is present in seawater, copper ions are oxidized. Although copper is an element necessary for the growth of all plants and organisms, it is not lipophilic and its low solubility causes bioaccumulation [2]. 1/2Cu2O(s) + H++ 2Cl−= CuCl2 − + 1/2H2O(l) (1) CuCl2 − + Cl−= CuCl3 2− (2)

Copper oxide paints are divided into two categories: soft and self-polishing/ablating paints. In soft paints, the primary component is copper oxide, suspended in the paint matrix. The copper oxide in soft paints dissolves over time, preventing the attachment of biological organisms on the surface.

Soft paints leave behind a honeycomb-textured layer after performing their antifouling function, and this layer is cleaned and repainted every few years. Self-polishing paints ablate the antifouling layer in a controlled manner. When the paint adjacent to water ablates, it removes organisms attached to the paint and the newly exposed surface continues its antifouling properties. Movement in water reduces paint thickness in a controlled manner, and ship hulls are repainted every 2 or 3 years [6-10]. In recent years, copper has been found to have negative environmental effects. Copper has been shown to be toxic to aquatic organisms, causing harm to larvae and fish species. For this reason, Baltic countries such as Sweden and Denmark have imposed restrictions on copper oxide antifouling paints. Additionally, the U.S. Navy has requested reduction in copper oxide content in paints [11]. Accordingly, various research has been conducted on paints that do not contain biocides and contain less toxic substances [12-21]. Research includes the use of ZnO in antifouling paints [22-23], prevention of biofouling through biomimetic models and surface creation [24-27], and research related to the inclusion of tannin and organic compounds in antifouling paints [28-32]. Although research into environmentally friendly antifouling paints is currently being conducted intensively, results with the desired properties have not yet been achieved. The developed environmentally friendly copper-free antifouling paint is protected by Turkish patent no. 2013/10673 and EP3044266 (A2), and the results of the research are shared in this article.

Experimental Work

The antifouling paint matrix was composed of various resins and resin combinations. Non-toxic nanomaterials and copper-free compounds were added. The resulting mixtures were applied to steel plates previously primed with suitable primer at a dry film thickness of 100 microns. These plates were placed in a test apparatus (Image 1) designed according to ASTM D4938 standards and subjected to testing in the Sea of Marmara under dynamic conditions for 270 days. Each sample was placed at an average depth of 50–80 cm below the water surface. Dynamic tests were conducted in the Moravia test rig at an average speed of 15 knots with a 4-hour operation period per week. The surfaces of the tested samples were evaluated according to ASTM D6990-05 standards and their performance was determined.

Test Results

Dynamic tests were conducted using a test apparatus designed according to ASTM standards located at a marina in the Bakırköy district of Istanbul and belonging to Moravia. Dynamic test conditions were determined and implemented in light of ASTM standards, operating periods of yachts navigating current seas, and Moravia's experience. Dynamic tests were initiated during a period when fouling organism reproduction rates were very high, and plates were continuously monitored over 9 months with changes observed. Samples were photographed at regular intervals, changes in the antifouling coating surface were examined, and comparisons were made with their initial state and the control group. Image 2 shows the state before dynamic testing of the control group (Control Plate) and two of our antifouling coatings (samples 1 and 2). The surfaces of all coatings were found to be quite smooth and shiny.

The condition of the plates shown in a, b and c in Image 2 after 4 months is shown in Image 3.

Upon examination of the control group (Image 3a), a dense fouling layer was observed on the surface, with this fouling layer created by both macrofouler and microfouler organisms (algae, barnacles, tube worms, etc.). The fouling rate is greater than 90%. Upon examination of the antifouling coating in Image 3b, a layer created by both microfouler and macrofouler organisms was observed on the plate surface. It was determined that almost all macrofouler organisms consisted of a species belonging to the crustacean class (tube worm). Although there was dense fouling (greater than 90%) around the antifouling coating, the fouling rate on the surface of this coating was less than 40%. In Image 3c, a dense fouling layer (greater than 90%) was observed around the antifouling coating, with this fouling layer created by both macrofouler and microfouler organisms (algae, barnacles, tube worms, etc.). By contrast, only the initial phase of fouling (micro slime layer) was observed in this coating. Another noteworthy aspect is that fouling did not occur in some areas at the boundary where the antifouling coating was absent.

Image 4 shows the condition of these plates after 9 months. Upon examination of the control group (Image 4a), fouler larvae (algae, barnacles, tube worms, etc.) that had settled on the surface were observed to develop over time, increasing their population and covering the entire plate surface (fouling rate 100%).

Upon examination of the antifouling coating in Image 4b, tube worm organisms were found to have proliferated on the plate surface, with the surface covered by many types of algae. Additionally, barnacle formation was observed to be quite minimal with insufficient development (fouling rate 99%). With regard to the performance of the antifouling coating in Image 4c, it was observed to yield better results than all other tested coatings. On the surface of the antifouling coating, algal spores were formed in some areas over the micro slime layer, but no marine crustaceans or larvae were found on the surface. In parallel, it was observed that fouling organisms around the antifouling coating were at lower density compared to other groups. The area on the right side of the antifouling coating was tested experimentally, and this accumulation on the surface was wiped with a finger to examine adhesion strength. This wiping was found to occur very easily, and with the wiping, the antifouling coating came to light, and it was confirmed that it had the quality to continue antifouling performance.

Conclusions

This study aimed to remove copper oxide, which has highly toxic effects on marine organisms, from existing antifouling paints and examine the antifouling performance of paints produced in different types and compositions containing non-toxic nanomaterials or environmentally friendly compounds. The work performed is in its initial stages, and when compared with the performance of seasonal or one-year antifouling life paints available on the market, the results obtained appear highly promising. Zeynel Abidin Karabay / R&D Manager - Moravia Boya ve Kimya San. Tic. Ltd. Şti. Gökhan Fidan / Product Development Manager - Moravia Boya ve Kimya San. Tic. Ltd. Şti. Hakkı Kalafatlar / Technical Manager - Moravia Boya ve Kimya San. Tic. Ltd. Şti. Dr. Yapıncak Göncü / R&D Manager - Bortek Bor Teknolojileri ve Mekatronik A.Ş. Prof. Dr. Nuran Ay / Department of Materials Science and Engineering - Anadolu University

References / References

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