Any object immersed in seawater will rapidly attract the attention of marine fouling from bacteria, algae (seaweeds) and animals such as barnacles, molluscs and tubeworms. Bacteria start to attach to this surface, forming a biofilm, which is a gel matrix made up of microorganisms.
This biofilm can induce corrosion, particularly due to the production of sulfides by bacteria. Once the biofilm is established, unicellular algae, barnacle larvae and spores of macroalgae attach and grow. They bind themselves to the surface, using proteins or other natural adhesives. There are 1,746 species of marine organisms which attach to marine constructions in seawater. The fouling of ships' hulls by marine organisms, even by slime, reduces speed and increases fuel consumption.
The effects of antifouling agents are usually obtained as a result of the slow leaching of compounds with biocidal effect from the coating. After using metallic compounds for hundreds of years, it was found in the 1970s that tributyltin (TBT) was an extremely effective antifouling agent, and by the end of the 1970s it was being used by 80% of the world's merchant shipping fleet. In the 1980s it was discovered that TBT contamination was adversely affecting other marine life, leading the International Maritime Organisation (IMO) to impose a global prohibition by January 1, 2008. In general, coatings are expected to have a lifetime of at least 3-5 years, preferably up to 7 years, since the cost of taking a large ship out of service for repainting is very high.
Today, three major types of antifouling paints are applied in the marine industry:
Self-Polishing Copolymer (SPC) coatings:
The polymer dissolves in a controlled manner in contact with seawater to release the enclosed biocide (typically CuO2) in a controlled way.
Hydrating or ablative coatings:
The biocide is leached from the pores of the polymer, which wears off slowly. Biocide release decreases over time and a leach layer is built up.
Fouling Release Coatings (FRC):
Biocide-free antifouling paint, in which silicone elastomers create a low-energy surface, preventing the marine life from attaching. No paint consumption.
Evonik's chemical tool box contributes to the
future development and performance of SPC and FRC coatings:
AEROSIL® fumed silica is mainly used to control rheological characteristics, as a thixotroping agent, as an anti-settling agent and to help in the prevention of rust and corrosion. Depending on your application, several hydrophilic or hydrophobic AEROSIL® fumed silica grades are available.
Dynasylan® SIVO 630 has been developed as a building block for the synthesis of silyl acrylate antifouling coating polymers.
Siloxane building blocks can be used in the backbone of FRC coatings.
Silane building blocks have been developed to improve the chemistry of SPC coatings .
The Silicone Epoxy Hybrid technology – like the SILIKOPON® EF – can be used for foul-release coatings in the maritime sector. With the Silicone Epoxy Hybrid technology robust, long lasting foul-release coatings can be formulated even as ultra-high solid coatings (below 100 g/l VOC). On top this technology provides outstanding anti-corrosion properties.