*Part of a series of articles from Sciencia Analytica on the importance of surface treatments and coatings to industry. See also The Importance of Surface Engineering and Coatings to UK Industry and Wealth
A large deep sea super tanker with a 550,000 tons dwt, (total weight of cargo that can be safely carried), cost millions to construct and commission. The vessels are equipped with the latest navigational and communications technology and entire nations are dependent on such vessels for trade and food security. It will therefore be surprising to many that the performance and profitability of this business is critically dependent on an outermost paint layer on the ship hull which is less than 100 microns thick.
This is because the hull of a ship can be rapidly colonised initially by a bacterial biofilm and subsequently by larger aquatic organisms such as barnacles and mussels which adhere to the hull and create a hydrodynamic drag in the water. This reduces the efficiency of the vessel and requires more energy in the form of fuel to reach a destination. The annual fuel bill for a 250,000-dwt tanker is $1.8m which can increase by $720,000 due to fouling. When considered across entire global fleets of 100,000 vessels this is a major concern. Also in addition to the fuel efficiency considerations, modern legislation on the Translocation of Species forbids the transport of certain marine species on ship hulls to other waters where they are not native to those waters.
The problem is not new and early adventurers in wooden sail boats experienced the problems of drag and reduced maneuverability. Christopher Columbus noted that such boats were coated in pitch or tallow to limit the attachment of barnacles, mussels and tube worms.
Modern marine paint coatings are therefore applied to ship hulls to limit or prevent the attachment of aquatic organisms. Originally all marine coatings relied on a biocidal effect at the surface of the paint layer. Biocides such as Tributyltin (TBT) were added to the bulk coating which then migrated out to the surface or were dependent on sacrificial layers being continuously eroded away on the voyage revealing a biocide rich surface. Such compounds have been replaced for environmental reasons by copper based materials which are effective in preventing hydrodynamic drag. Research continues into new alternatives and recent publications describe enzyme based coatings where an enzyme is incorporated into a paint system with a nutrient which when digested releases a biocide or generates a biocidal effect.
However increasing legislation and potential concerns on the environmental effects of biocides has led to the development of foul release coatings which are non-biocidal and rely on physical effects to limit or prevent attachment.
It has been found that when paint binders, composed largely of silicone polymers or silicone and fluoropolymer blends, are formulated into marine paints they have a highly hydrophobic surface finish or sometimes an amphiphilic effect. These formulations make it difficult for aquatic organisms to use secreted protein compounds to adhere to the surface and those that do so are quickly sloughed off the surface by the force of water during the voyage. Many foul release coatings perform well in dynamic conditions at sea but less well in harbour and in warm tropical waters. There is a great deal of ongoing research to try to maximise the performance of foul release marine coatings.
X-Ray Photoelectron Spectroscopy (XPS) is a powerful surface analysis technique which is capable of detecting and mapping the distribution of additives such as biocides at the surface, subsurface or through a cross section of a paint film.
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Marine paints are an excellent example of the importance of surface coatings. The total Marine Coatings Market size will surpass USD 15 billion by 2024, at approximately 7% CAGR from 2016 to 2024. There is a growing need for low fuel consumption will enhance the demand for regular coating by anti-fouling agents, propelling the overall marine coatings market. Moreover, stringent regulatory norms impel the usage the usage of high cost and environment friendly marine coatings. The marine coatings market has been segmented into coastal, deep sea, containers, offshore vessels, leisure boats, and others on the basis of application. Coastal application includes dredgers, fishing vessels, tugs, passenger/cargo ferries, offshore supply vessels, defence ships, and coasters. This segment generated more than $3bn in 2016. and will likely rise owing to growing disposable income of the population of North America and Western Europe. High maintenance of leisure boats, yachts, cruise ships, etc. will characterize the marine coatings market demand in this segment. This segment generated over USD 1bn at a CAGR of 7% up to 2024. Source Global Market Insights Jan 2017.