Marine biofouling and antifouling coatings

1. Environment and Mitigation Marine biofouling and antifouling coatings L. Goodes1, M. Salta1, S. Werwinski1, S. Dennington1, J.A. Wharton1, R.J.K. Wood1, K.R. Stokes1,2 1 national Centre for Advanced Tribology at Southampton (nCATS), School of Engineering Sciences, University of Southampton, Highfield, SO17 1BJ, UK. 2 Physical Sciences Department (Dstl), Dstl Porton Down, Salisbury, Wiltshire, SP4 0JQ, UK. Introduction and background Marine biofouling is defined as the undesirable accumulation of microorganisms, plants, and animals on artificial surfaces immersed in sea water. In the case of the underwater hull of a ship, the adverse effects caused by this biological settlement include: • High frictional resistance, due to generated roughness, which leads to an increase of weight and subsequent potential speed reduction and loss of manoeuvrability. To compensate for this, higher fuel consumption is needed, which causes increased greenhouse gas emissions. • It may also necessitate heavier and less energy efficient machinery. The increase in fuel consumption can be up to 40%. • An increase in the frequency of dry-docking operations, i.e. time is lost and resources are wasted when remedial measures are applied. Potentially harmful waste is also generated during this process. • Deterioration of marine polymeric coatings so that corrosion, discolouration, and changes in the electrical conductivity can occur. • Introduction of marine species into environments where they were not naturally present (invasive or non-native species). Research impact The fundamental underpinning science derived from the work has led to a very successful and recognised international collaborative programme between the United Kingdom, France and the Netherlands. The project will develop a greater understanding of the influence of biofouling and the impact natural product antifouling coatings for ships. Although the incorporation of tributyl tin (TBT) into coating systems has been widely used for its anti-fouling capacity, recently the use of TBT has been banned due to its toxic affects in the wider marine environment. Furthermore, fresh concerns about the long-term effects of copper pollution in environmentally important estuaries and offshore areas are providing an incentive to study new antifouling solutions. Therefore, the need for new, effective and environmentally friendly coating systems has been the focus and challenge for the scientific community. The ideal antifouling coating would prevent marine growth as well as maintain a long performance life while keeping within increasingly strict environmental regulations. • Project objectives • Evaluation of emerging technologies to obtain environmentally friendly antifouling coatings with projected long term performance (6-10 years); • Development of advanced accelerated test methods for assessing new natural products, including biocide free coatings, within a short period (< 1 year) which is representative of long-term in-service performance. Discussion In the marine environment, a wide variety of species illustrate antifouling abilities by several means, e.g. the use of chemical and physical defences, symbiotic relationships between host (e.g. algae) and epibionts (e.g. bacteria) that prevent fouling. The impediment of biofouling in a natural way, as observed in marine organisms, has triggered the scientific interest and led to the examination of marine natural products as a possible route for a novel antifouling technology. Nearly 20,000 natural products have so far been described that originate from marine organisms. Since the early 1980s, a great number of marine natural products have been assayed against organisms implied in the biofouling process and several reviews dealing with their potential use as novel antifouling biocides have been realised. Marine polymeric coatings, like most paint compositions, are made up from a binder and a series of pigments which include additives, colour and extenders. The antifouling additives are included in the top-coat or final coating layer of the multi-coat marine antifouling system. Thus, the binder and solvent selection need to be carefully tailored to the chemical properties of any new potential biocide molecule. This collaborative research programme between the University of Southampton, the Institut des Sciences de l’Ingénieur de Toulon et du Var (France) and TNO (Netherlands) will investigate: Survey and screen new types of emerging binders for effectiveness as a self-polishing copolymer, e.g. block silylated binders, see Fig. 2. Survey and screen new specific (natural product) biocides for antifouling efficacy and toxicological properties. Extracts of algae such as:(a) Chondrus crispus and (b)Bifurcaria bifurcata. Characterisation of antifouling paint formulations byerosion, adhesion and mechanical properties. Fig. 2: Chemical structure of the silylated binder Fig. 3: Examples of Chrondrus crispus and Bifurcaria bifurcata. Fig. 1: Hull foulinf by (Top) brown algae and (Above) the green algae ‘Ulva enteromorpha’. Worked sponsored by