(96d) Modeling of Conductive Antifouling Paints for Marine Applications

Protection from fouling organisms (biofouling) is a key function of coatings on marine hydrokinetic (MHK) devices. Accumulation of biomass on devices risks performance degradation and possible failure. At the present there are no proven reliable options for prevention of fouling in the marine environment with applications to match device lifetimes expected to be on the order of 10-20 years. Removal, cleaning, and re-application of short-lived antifouling paints is an expensive prospect. Long term solutions for antifouling protection need to be identified and tested for reliability. Electrified conductive paints have been shown to be effective in the prevention of marine biofouling and may be a viable solution for long term antifouling performance[1] . The present work seeks to further the understanding of the mechanism of action and to develop the engineering knowledge needed to enable application.

The mechanism of action has been proposed variously to be direct electron transport[1], electromagnetic field repulsion[2], and electrochemical reaction[3, 4]. Evidence suggests that electrochemical oxidation of chloride and bromide present in seawater produces strongly oxidizing agents which sanitize the surface being protected. These oxidizing agents are short lived in the environment with end states being the original chloride and bromide. Comparison of the experimentally determined minimum potential needed for biofouling protection with Tafel plots in sterilized and newly acquired seawater support this hypothesis, as does cyclic voltammetry.

Chloride oxidation at graphitic anodes has been studied in highly saline water at high over-potential for the chloralkali process. The salinity, current density, product concentration, and pH conditions of the chloralkali process are vastly different from the conditions at a protected surface in the natural marine environment with current density on the order of 20µA/cm². Determination of reaction products and reaction selectivity under the applicable conditions is necessary to allow design of electrochemical antifouling systems. The present work utilizes a well characterized millimeter scale laminar flow electrochemical reactor and amperometric methods to determine reaction products, which yields reaction selectivity.

In order to evaluate the longevity of conductive antifouling coatings in marine applications accelerated aging methods are required. Standard procedures for rapid aging of marine paints involve exposure to ultraviolet light, moisture, temperature swings, and salt fog[5]. The two primary concerns for MHK applications are adhesion and electrochemical performance. The existing test regimens do not address electrochemical performance; therefore in addition to the standard tests accelerated aging methods using high over-potentials and current density have been developed. The electrode selectivity is characterized throughout the aging process, which enables prediction of performance losses.

Aged coatings have also been deployed in the marine environment to validate performance after aging. A standard procedure for washing test coupons to remove loosely adhered debris using consistent shear stress followed by visual and microscopic inspection has been developed as a means to standardize determination of antifouling efficacy.

[1]          T. Matsunaga, T. Nakayama, H. Wake, M. Takahashi, M. Okochi, and N. Nakamura, "Prevention of marine biofouling using a conductive paint electrode," Biotechnol. Bioeng., vol. 59, pp. 374-378, // 1998.

[2]          T. Nakayama, H. Wake, K. Ozawa, N. Nakamura, and T. Matsunaga, "Electrochemical prevention of marine biofouling on a novel titanium-nitride-coated plate formed by radio-frequency arc spraying," Appl. Microbiol. Biotechnol., vol. 50, pp. 502-508, // 1998.

[3]          R. E. Perez-Roa, M. A. Anderson, D. Rittschof, C. G. Hunt, and D. R. Noguera, "Involvement of reactive oxygen species in the electrochemical inhibition of barnacle (Amphibalanus amphitrite) settlement," Biofouling, vol. 25, pp. 563-71, // 2009.

[4]          J.-R. Huang, W.-T. Lin, R. Huang, C.-Y. Lin, and J.-K. Wu, "Marine biofouling inhibition by polyurethane conductive coatings used for fishing net," J. Coat. Technol. Res., vol. 7, pp. 111-117, // 2010.

[5]          Paint and Coating Testing Manual : 15th edition of the Gardner-Sward handbook: ASTM International, 2012.