Antifouling paints
Definition of antifouling paints:
A marine paint containing poisonous ingredients which prevent or retard fouling or marine underwater growth on ship bottoms, hulls, nets, piles, etc.
This is the common definition for antifouling paints, other definitions can be discussed in the article
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Contents
Tributyltin
Previous antifouling paints contained the chemical tributyltin (TBT) that was banned in 2001 by the International Maritime Organization (IMO, Antifouling Convention). Tributyltin paint was widely used in the 1970s and 1980s as a highly efficient biocide in antifouling paints for ship and boat hulls. TBT was also used as a biocide in a range of other applications including refrigeration systems, wood pulp, leather processing, wood preservation processes and textile treatments. Ecotoxicologists discovered already in the 1970s strong endocrine disrupting effects on growth, development and reproduction (imposex) in sensitive species groups such as oysters, neogastropod snails (dogwhelk) and mud snails. TBT typically has a half-life of 1–5 years in well-oxygenated surficial sediments, but TBT accumulated in fine-grained anoxic marine sediments persists over several decades. Despite observations of reduced TBT concentrations in many marine sediments over the recent decades, contaminant hotspots are still prevalent worldwide around shipyards, fishery harbors and marinas[1].
Non-biodegradable antifouling paints
Today, antifouling paints often still contain non-degradable antibacterial compounds such as cuprous oxide (Cu2O) and/or zinc pyrithione embedded in self-polishing resin-based coatings. Hydrolytic reactions within the coating matrix gradually erode the coating on the hull surface, releasing the embedded toxic substances, while continuously exposing a fresh smooth surface in a layer-by-layer manner as the coating degrades. Released non-degradable toxic compounds can accumulate in marine biota and therefore pose a serious environmental risk. Of special concern are the antifouling paint particles generated during the maintenance of boats and shed from abandoned structures and grounded ships, which are highly detrimental to benthic organisms. [2][3]
Experiments are being conducted with nano-antifouling coatings. These coatings gradually release nanomaterials with antibacterial properties, such as nanosilver, which inhibit the growth of marine organisms. The nanoparticles penetrate microbial cells and disrupt microbial activity by generating reactive oxygen species (ROS). However, challenges such as aggregation and uncontrolled release of silver nanoparticles currently limit their broader applicability.[4]
Investigated antifouling paints with natural antibacterial substances embedded in a self-polishing polymeric matrix [5] Essays with positive results have been reported for the natural organic biocides capsaicin, indole derivatives, camphor, albofungin, ceramide, paenol, gallic acid persulfate and xanthone embedded in acrylic resin-based coatings, for the biocides furan, cholic acid, chalcone, camptothecin, diterpenoid, dipeptide in rosin-based coatings, for the biocides chalcone, butenolide and phidianidine in polyurethane coatings, for the biocides sodium salicylate and maleimide in epoxy resin coatings, for the biocide capsaicin in high-density polyethylene (HDPE) coatings, and for the biocides gallic acid persulfate and xanthone and methyl deoxycholate in epoxy resin coatings.
Natural biocidal additives
Natural antimicrobial agents (or synthetic derivatives) can be used instead of non-biodegradable additives. Many marine organisms (e.g. sponges, corals) protect themselves by producing secondary metabolites with biocidal activity. These organic compounds can also serve as antifouling agents and can be chemically synthesized. Natural organic biocides are actively investigated, as additives to self-polishing polymeric coatings (epoxy, rosin, acrylic, silicone, polyurethane, and others), see the textbox. The antifouling performance depends on the compatibility of the antimicrobial agent with the polymeric matrix. Although polymeric matrices are the essence of the coatings, other constituents, such as solvents or diluents, additives, pigments, crosslinkers, and extenders, are also essential for the coating formulation. Investigations are still ongoing to optimize the performance of these paints.[4]
Low surface-energy coatings
Silicone-based anti-fouling coatings are being studied as low surface-energy coatings. Low surface-energy anti-fouling coatings are a type of marine coating designed to prevent biofouling by reducing the adhesion between the coating surface and marine organisms. The molecular structure of the coating surface significantly diminishes van der Waals forces, hydrogen bonding, and other physicochemical interactions between the coating and the fouling organisms (such as bacteria, algae, and mollusks), thereby effectively delaying their attachment and preventing biofouling, thus enhancing surface cleanliness. Silicone oils, specifically linear polydimethylsiloxane products, migrate from within the coating to the surface during a vessel’s journey, creating a smooth oil film. This film helps in removing contaminants by water flow, thereby preventing fouling and decreasing cleaning and maintenance frequency. Compared with traditional coatings, these materials are non-toxic, environmentally friendly, and have a longer service time. However, achieving long-term stability in harsh marine environments and effectiveness against a broad spectrum of biofouling organisms are still challenging objectives.[4]
Zwitterionic polymer coatings[6] Zwitterionic polymers (also known as polybetaines) are an alternative class of hydrophilic antifouling materials. They form a dense hydration layer underwater, deterring the adhesion of fouling organisms by inhibiting protein adhesion. This is due to their specific chemical structure which has opposite charges in each repeating functional group. Good results were obtained when zwitterions were added to raw lacquer, a natural resin coating with Urushiol as the primary component. Urushiol formed a stable interface with the functional groups of zwitterionic compounds through covalent or non-covalent bonds. Urushiol polymer coatings have a smooth and compact texture, high hardness, good stability, and resistance to organic solvents and chemical corrosion. However, the costs of producing zwitterionic polymers limit their practical use.[7]
Bioinspired polymer matrices such as hydrogels, slipper liquid-infused porous surface (SLIPS), zwitterionic polymers, and other biodegradable matrices are also considered as candidates for antifouling coatings.[5] The principle of biodegradable coatings lies in the fact that a surface constructed from a biodegradable polymer would gradually decompose by erosion or by enzymatic action in seawater. The attached living organisms or inorganic substances are thereby polished, resulting in a self-renewing surface. Several research groups have developed coatings based on biodegradable polyurethanes with interesting antifouling potential and without a negative impact for the marine environment.
Biometric anti-fouling coatings
An alternative are the biometric anti-fouling coatings that mimic the microstructures observed in many marine animals (e.g. dolphins, sharks and shellfish). The micro- or nano-scale roughness of these surfaces reduces the contact area between water droplets and the solid surface, thereby decreasing the adhesion of fouling organisms. [8] These microstructures disrupt the physical adhesion of marine organisms such as barnacles, algae, and bacteria. Despite their environmental benefits, these low surface energy coatings face limitations due to the complexity of their surface microstructures, limited mechanical strength, and difficulties in repair.
Legal regulations
The regulatory policy for self-polishing coatings is primarily governed by the 2001 International Convention on the Control of Harmful Anti-fouling Systems on Ships (AFS Convention), which explicitly prohibits the use of toxic organotin compounds, such as tributyltin (TBT), as active ingredients in self-polishing anti-fouling coatings. The European Union’s Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) regulation imposes strict requirements for the registration, evaluation, and authorization of chemicals used in self-polishing anti-fouling coatings, to ensure that they do not cause irreversible damage to aquatic ecosystems.
Related articles
- TBT
- TBT and Imposex
- TBT and intersex in periwinkles
- Coastal pollution and impacts
- Endocrine disrupting compounds in the coastal environment
References
- ↑ Beyer, J., Song, Y., Tollefsen, K.E., Berge, J.A., Tveiten, L., Helland, A. Oxnevad, S and Schoyen, M. 2022. The ecotoxicology of marine tributyltin (TBT) hotspots: A review. Marine Environmental Research 179, 105689
- ↑ Soroldoni, S., Vieira da Silva, S., Braga Castro, I., de Martinez Gaspar Martins, C. and Lopes Leaes Pinho, G. 2020. Antifouling paint particles cause toxicity to benthic organisms: Effect on two species with different feeding modes. Chemosphere 238, 124610
- ↑ Muller-Karanassos, C., Arundel, W., Lindeque, P.K., Vance, T., Turner, A. and Cole, M. 2021. Environmental concentrations of antifouling paint particles are toxic to sediment-dwelling invertebrates. Environ. Poll. 268, 115754
- ↑ 4.0 4.1 4.2 Wu, S., Wu, S., Xing, S., Wang, T., Hou, J., Zhao, Y. and Li, W. 2024. Research Progress of Marine Anti- Fouling Coatings. Coatings 14, 1227
- ↑ 5.0 5.1 Pereira, D., Almeida, J.R., Cidade, H. and Correia-da-Silva, M. 2024. Proof of Concept of Natural and Synthetic Antifouling Agents in Coatings. Mar. Drugs 22, 291
- ↑ Xu, K., Xie, H., Sun, C., Lin,W., You, Z., Zheng, G., Zheng, X., Xu, Y., Chen, J. and Lin, F. 2023. Sustainable Coating Based on Zwitterionic Functionalized Polyurushiol with Antifouling and Antibacterial Properties. Molecules 28, 8040
- ↑ Murali, S., Agirre, A., Arrizabalaga, J., Rafaniello, I., Schaefer, T. and Tomovska, R. 2024. Zwitterionic stabilized water-borne polymer colloids for antifouling coatings. Reactive and Functional Polymers 196, 105843
- ↑ Król, B., Król, P., Byczynski, L. and Szalanski, P. 2017. Methods of increasing hydrophobicity of polyurethane materials: Important applications of coatings with low surface free energy. Colloid. Polym. Sci. 295: 2309–2321
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