Making ship hulls invisible for microorganisms
“Biofouling is one of the last unsolved problems in the coatings industry. Up to this point we had not succeeded in finding the optimal solution for ship coatings. This is why antifouling coatings are a core topic at our new ‘Smart Surface Solutions’ Competence Center,” says Stefan Silber, head of Innovation Management Coating Additives in Evonik’s Resource Efficiency Segment.
Forming amphiphilic polymers
To protect ship hulls against biofouling, scientists combine a hydrophobic silicone with a hydrophilic polymer. This results in the formation of amphiphilic polymers. The hydrophilic domains attract water to the ship’s hull. This builds a sort of water shell around the polymers, camouflaging the hull from the organisms. The alternation with water-repellent domains further confuses the organisms: They can no longer clearly recognise the surface, nor distinguish the hull from sea water. As a result of this uncertainty they usually stay away from the hull altogether.
If the microorganisms do nevertheless try to settle on the hull, the second defense mechanism of the hydrophobic domain – its anti-adherent action – should come into play: The base material for the new solution against biofouling, the “Silikopon EF” silicone hybrid resin, makes it difficult right from the start for the organisms to settle on the hull. This is because the low surface tension and smooth surface of the silicone give it easy-clean properties. The organisms cannot readily adhere to the hull, and the few that do succeed should be dislodged by the water stream, even at low ship speeds.
Field tests prove efficacy
Field tests under real conditions have already proven the basic efficacy of the new hybrid systems. The scientists are now working jointly with the industry on coatings based on the new systems. They are also confident of being able to increase the interval between successive applications of the coating in the future. This would enable shipping companies to reduce maintenance costs as well as the negative effects of biofouling, such as high fuel consumption.