Marine paints: These are the challenges they have to overcome
Some 60% of a ship’s driving power is expended on overcoming frictional resistance. Manufacturers of marine coatings have a great opportunity here to help their customers to substantially reduce frictional resistance by developing innovative coating systems. That would have the effect of reducing two E’s, namely emissions and energy.
Multifunctional – not again!
Such coatings would be expected of course to exert outstanding antifouling and anticorrosion effects. Oh, as well as that, they should be environmentally friendly to ensure that emissions – in other words, bisphenol A from epoxy coatings – should be minimised when end-of-life ships are dismantled in scrap yards. Can a coating system really do all this? Sounds to me (again) as if we want to have our cake and eat it.
How things stand
The IMO (International Maritime Organisation) estimated in 2009 that, in the absence of corrective action and the introduction of new technologies, fuel-related air emissions from the global shipping fleet could rise by 38% to 72% by 2020. Antifouling coatings can save $ 60 bn annually on fuel and reduce CO2 emissions by 384 million tonnes.
No wonder there are so many projects investigating this topic. These range from studies of self-polishing surfaces to fouling-release through to omniphobic surfaces. All of them seek to avoid colonisation by marine organisms as a way of reducing the frictional resistance. Many projects that looked for or are still looking for alternatives were spawned after the total ban on organozinc-based biocides in 2008 .
I am particularly drawn to an EU-funded project on “Low Emission Antifouling” (LEAF), which has developed an environmentally friendly antifouling paint that is based neither on biocide emissions nor on low adhesion. Instead, this prototype exerts its antifouling effect through direct contact between a fouling organism and biocides contained in the coating. This approach has the added benefit of extending the service life and lowering maintenance costs (leaf-antifouling.eu). The project has concluded in the meanwhile, but the project partners continue to work together to commercialize the product.
Potential BPA emissions from epoxy applications
After epichlorohydrin (ECH), bisphenol-A (BPA) is a key constituent of epoxy resins. It is estimated that some 85% of the global production of epoxy resin is made by the chemical reaction of ECH and BPA.
The Epoxy Resin Committee (ECR; www.epoxy-europe.eu) believes that up to 20% of the epoxy used for marine coatings could be lost during paint application (e.g. through dripping) or as paint wastage (e.g. unused paint after the coating process), end up incinerated or enter the sewerage system. Of the 51,000 tonne of epoxy used annually for marine coatings, it is estimated that about 398 kg of residual BPA could be thermally degraded, while about 96 kg could be released into water bodies. During service life, the biggest source of release is decks coated with epoxy-based topcoats which are susceptible to UV radiation. The number of ships with epoxy-coated decks is not known. Waste handling of end-of-life ships would pose the highest possibility of BPA release for marine coatings. Up to 95% of European ships are dismantled in Asian countries by unclear practices. The European Commission regulation on handling end-of-life ships does not come fully into force until 2020, and will only apply to ships with EU flags. Thus some ships may change flag to avoid the new requirements. In total, the degradation of 8,000 tonnes of epoxy resins in marine coatings from the 350 European ships could lead to 388 kg of residual BPA being released into the environment annually.
BPA-free epoxies: sooner or later!
I believe it is only a matter of time before freedom from BPA becomes mandatory for marine coatings as well. Sooner or later, Asian countries, too, will tighten up their laws and regulations – they are already showing signs of doing so. Furthermore, numerous projects and studies on the development of BPA-free epoxies are also available. For example, an interesting study (Technical Report No. 66) dating from 2013 by Robert J. Romano and Daniel F. Schmidt, University of Massachusetts Lowell, USA, looks at the synthesis of high-performance BPA-free epoxy resins. There are numerous products for coating applications in the food industry (e.g. beverage cans) already on the market. Yet for heavy-duty corrosion protection – needed for coating ships – there are no products currently available. So anyone planning for the future needs to address this issue now.