This is a news headline. Invisibility Cloak for Ships

Evonik currently has effective solutions for anti-fouling (toxic) paints in its product portfolio. However, group researchers are now working on new raw materials for paints and coatings that use less biocide or eliminate biocide use entirely to effectively protect ship hulls against biofouling. Sea transport is the preferred choice for cargo shipping. Nearly 90 percent of all goods transported around the world are carried on more than 50,000 ships operating on the world's oceans. The continuity of global commercial fleets depends largely on the external hulls of ships. Biofouling, caused by the proliferation of plants and marine organisms in the submerged part of the hull, is a particular and specific problem. Proteins, carbohydrates and other micronutrients in the ocean attach to the hull just seconds after the ship's hull comes into contact with seawater. All these nutrients subsequently attract marine organisms that will attach to and settle on the hull. The biofilms formed by all this on the hull are extremely complex habitats where hundreds of species interact with each other positively or negatively. These habitats disrupt and prevent ships' passage through the world's oceans (Figure 1). Figure 1: Formation of biofilms - Microorganisms settle on the hull just seconds after the ship comes into contact with water. They serve as a food source for other organisms and a biofilm forms. Significant roughening of the hull surface due to biofouling causes a very serious increase in friction resistance during voyage. This results in a vicious cycle in which the ship requires more energy and fuel to maintain the same speed of travel and CO2 emissions increase. Current research shows that even light calcification increases fuel consumption by up to 30 percent. Additionally, the ships' maneuverability is reduced and corrosion risk increases. Consequently, ships need to spend more time in dry dock for cleaning and repairs. Frequently repeated maintenance cycles and increased fuel consumption result in higher costs for shipping companies. Beyond all this, global climate is also affected by this situation: Even a thin biofilm causes CO2 emissions of over 270 million tonnes per year. Therefore, there is high demand for paints that protect ship hulls from the effects of biofouling. These toxic (anti-fouling) paints prevent the settlement of marine organisms, eliminating the negative effects of biofouling. However, finding the right coating is a challenging and difficult task. The most effective method known to date for protecting ships' hulls is toxic paints containing biocides. These paints work through a leaching process in which active toxic substances dissolve from the paint structure and reach the surface of the ship hull. These toxic substances create a kind of biocide cloud around the ship, damaging microorganisms before they settle on the hull. The most well-known of the biocides is tributyltin hydride (TBT), an organometallic compound of tin. However, this application creates a problem: Research shows that the toxicity of biocides is not limited only to organisms on the hull surface, but also affects other living species in the sea. For example, even low concentrations of TBT inhibit shell growth in Pacific rock oysters. TBT increases imposex in snails and other species, a condition in which female marine organisms develop male reproductive organs and male marine organisms develop female reproductive organs, and consequently reproduction becomes impossible and species face extinction. For this reason, the use of TBT-based underwater paints to protect marine organisms has been banned worldwide. Furthermore, no biocides based on toxic tin, arsenic or mercury compounds can now be used. This has led to a search for other coating and paint options that are equally effective but also environmentally friendly. However, despite all notable efforts, a fully satisfactory solution to the problem has not yet been found. Due to the lack of suitable alternatives, biocides continue to be used in anti-fouling paints. Today, copper oxide is preferred instead of TBT as an active ingredient, considered more environmentally friendly than TBT and based on the same mechanism of action as TBT. However, this substance is also a heavy metal oxide. Copper ions dissolved from the paint can also be toxic at high concentrations. Therefore, the search for a better anti-fouling solution continues.

Biocide-free coatings

Evonik is stepping in to find just this solution. The Paints and Coatings Additives division is working to establish a "Smart Surface Solutions Center of Excellence" to solve problems awaiting resolution in paint technology. This team also plans to develop an alternative to existing anti-fouling solutions with a completely environmentally friendly product that contains no biocides. Researchers are transferring their existing expertise in utilizing silicone effectively to this area as well. The high non-stick properties of the SILIKOPON® EF silicone-epoxy hybrid resin system in Evonik's portfolio make it difficult for microorganisms to settle from the start. This is possible thanks to the smooth surface of the hybrid system and its very low surface tension. Organisms such as algae, bivalves and barnacles find it difficult to adhere to this surface. Even if they initially succeed in adhering, once the ship begins to move at low speeds, water currents detach them from the surface, making it easy to clean due to its smoothness. In addition to all this, SILIKOPON® EF also provides high mechanical and chemical resistance that prevents long-term corrosion damage. Researchers, while using these benefits, want to add another new property: The new binder of these paints should prevent organisms from noticing the hull, so that they do not adhere to it at all. For this purpose, scientists are combining hydrophobic silicone with hydrophilic polymer to produce a material known as amphiphilic polymers, in which hydrophilic and hydrophobic regions alternate (Figure 2). Hydrophilic regions form a water film around the polymer that masks the surface against organisms. Organisms become confused in this case, cannot identify the surface and prefer not to settle (Figure 3). Researchers are taking advantage of a known natural principle here: Living organisms always search for the most suitable habitat for reproduction.

Figure 2: Combining benefits - Scientists combine hydrophobic silicone with hydrophilic polymer using a hardening catalyst.

Figure 3: Biofouling prevention protection - In the new system, hydrophobic and hydrophilic regions alternate. Organisms become confused and cannot identify the surface.

Cost reduction

Researchers are moving forward with confident steps on the path to finding a solution. In tests conducted, they were able to demonstrate that the raw materials of this newly developed paint are non-toxic and more effective compared to binder systems currently used in the market. The goal is to work in close cooperation with customers to develop durable and protective paints based on these polymers. Researchers are optimistic that they will soon be able to extend the repainting intervals for ships. In this way, shipping companies will be able to reduce the maintenance costs of their ships while overcoming the damage caused by fouling. To achieve this, researchers use various test methods to improve the optimization of binder material systems. Through collaboration with Münster University, new screening tests have been developed that allow the anti-fouling performance of coatings to be predicted just six weeks after application. If a tested substance shows undesired toxic properties in the initial laboratory test, it is rejected or the formulation is reconsidered. On the other hand, if the substance shows promise, it is tested at sea. Experts immerse many coated test panels in the sea between March and October each year. In this process with high "growth pressure", the biofouling tendency proceeds at the highest level. The actual rate of growth development under real conditions becomes more apparent. Only then does it become possible for researchers to reliably evaluate the effectiveness of new formulations. The reason Evonik is not only developing a completely new solution but also working to further advance existing anti-fouling coatings is this. Researchers in the Paints and Coatings Additives division have developed a new AEROSIL® silica with hydrophilic modification that significantly improves the effectiveness and service life of anti-fouling paints. Paint manufacturers can use this product in their formulations together with copper oxide to extend the life and effect of the paint introduced to the market as VP 4200. VP 4200 reacts with copper oxide, fixing it to the film and making it harder and more resistant. Consequently, copper oxide can be used for longer. If 10 percent VP 4200 is added to the liquid paint formulation, effective protection against biofouling can be provided with approximately 6 percent copper oxide content. This means the paint contains 80 percent less copper oxide than conventional formulations that normally contain 30 percent or more copper oxide. AEROSIL VP 4200 dispersed in a system containing Cu2O.

Dispersion without VP 4200

Dispersion with 10% VP 4200

  Dr. Katrin Roland Evonik Research and Development Center Head of Anti-Fouling Division       Dr. Michael Fiedel Evonik Research and Development Synthesis Unit Head       Translation: Duygu Özgün Evonik Paints Additives Department Business Manager