Natural products for antifouling coatings

Chambers, L.D., Wood, R.J.K., Walsh, F.C. and Stokes, K.R. (2007) Natural products for antifouling coatings. Marine Corrosion Forum, London, UK. 10 Oct 2007.

Abstract

Biofouling of marine structures and platforms results in both economical and environmental penalties. Current approaches to marine antifouling increasingly adopt strategies to minimise their environmental impact. One approach is to successfully mimic nature’s methods to control biological growth. A key biomimetic development for marine antifouling coatings is the isolation and use of marine natural products. Such chemicals are needed for secondary metabolic requirements of plants and animals, including defence chemicals. Recent work has focused on isolation and bioassaying techniques but few studies have trialed natural product compounds in a functional coating system.
A recent project in our laboratories has used a multidisciplinary approach to develop an antifouling coating system using environmentally acceptable and naturally occurring products. A red algal natural product extract from Chondrus crispus has been evaluated as a potential antifoulant. The ethanol extract was successfully screened with a bioassay which included a range of biofouling organisms; marine bacteria, microalgae and macroalgae. The natural product extract was directly incorporated into a proprietary coating mixture to assess its activity through a realistic delivery mechanism and to test if its addition affected the coating matrix. The latter was tested in 3.5 % NaCl solutions using electrochemical impedance spectroscopy (EIS) and open-circuit potential (OCP) electrochemical techniques.
The incorporation of the algal extract into the coating resulted in a slightly more negative corrosion potential of the coated mild steel by 30 mV (Ag/AgCl reference), and did not affect the impedance characteristics when compared to the control coating with no antifoulant. This suggests that the direct use of the natural product extract in the coating is an effective way to test antifouling activity for future compounds. The antifouling activity of the experimental coating was tested in seawater. Biofilm growth on the coating surfaces was examined using a bacterial viability nucleic acid stain and an episcopic differential interference contrast (EDIC) microscope. This proved to be a rapid tool for the examination of growth patterns and distribution of bacteria in-situ. Field trials were used in the Solent, England and showed a visual antifouling delay of 6 weeks in comparison to the negative control. The development of a functional antifouling coating should be possible using an aqueous phase solution such as a marine natural product.

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Contributors

Author: R.J.K. Wood

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