Answer
"Initially ships used highly toxic antifouling compounds, later TBT self-polishing paints became very successful, but due to severe environmental toxicity TBT was prohibited under the IMO AFS Convention. Industry then moved to TBT-free copper-based biocidal coatings, controlled-depletion and self-polishing copolymer paints. Modern development is toward silicone or fluoropolymer foul-release, hydrogel and low-friction coatings. A recent regulatory development is the prohibition on applying or reapplying anti-fouling systems containing cybutryne from 1 January 2023.
The evolution of marine anti-fouling coatings spans distinct technological generations driven by performance needs and environmental regulations:
[1] Biocide Leach (1950s-70s) --> [2] TBT Self-Polishing (1970s-2000s) --> [3] Copper/SRA Ablative (Modern) --> [4] Foul Release Systems (Latest)
- 1st Generation – Conventional Insoluble Matrix Coatings (Biocide Leaching): Hard matrix paints releasing cuprous oxide ($Cu_2O$) via leaching. Pores clogged quickly, leaving a rough hull shell.
- 2nd Generation – Organotin / Tributyltin (TBT) Self-Polishing Copolymer (SPC): Highly effective chemical bonding with organotin. The paint layer hydrolyzed and dissolved slowly under hydrodynamic action, self-polishing the hull surface. Banned globally in 2008 by the IMO AFS Convention due to severe eco-toxicity (shell deformation in oysters, imposex in whelks).
- 3rd Generation – TBT-Free Self-Polishing Copolymers: Replaced TBT with Copper-based compounds (Cuprous Oxide, Copper Pyrithione) and organic booster biocides (e.g., Zineb, Irgarol) bound to acrylic or silyl polymer bases.
- 4th Generation – Non-Biocidal Foul-Release Coatings (Silicone & Fluoropolymer): Modern ultra-smooth, low surface-energy silicone/fluoropolymer coatings. They contain no chemical biocides; instead, they create a slippery non-stick surface preventing organisms from adhering permanently—fouling detaches naturally as the ship navigates at speeds >12 knots.
- 5th Generation – Nano-Structured & Biomimetic Coatings: Current technological frontier utilizing nano-composite structures mimicking shark skin (denticles) to mechanically resist bio-attachment without environmental contamination.