Final Report: Copper-Free Antifouling CoatingsEPA Contract Number: 68D03016
Title: Copper-Free Antifouling Coatings
Investigators: Walsh, M. Alex
Small Business: E Paint Company
EPA Contact: Manager, SBIR Program
Project Period: April 1, 2003 through September 1, 2003
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2003) RFA Text | Recipients Lists
Research Category: Nanotechnology , SBIR - Nanotechnology , Small Business Innovation Research (SBIR)
This Phase I research project sought to develop novel copper-free antifouling coatings by creating bioactive polymers that prevent attachment of biofouling organisms through nontoxic means. An approach that mimics nature was proposed. Like the angiosperm Zostera marina (eelgrass), which produces effective concentrations of zosteric acid to deter settlement of biofouling larvae, the proposed coating releases analogous compounds by hydrolysis of the self-polishing surface.
The January 3, 2003, International Maritime Organization deadline for application of organotin coatings is now past, and the industry is shifting to the next generation of antifouling coatings. The most promising candidates are self-polishing coatings based on copper, zinc, and silyl acrylate polymers filled with cuprous oxide and U.S. Environmental Protection Agency-approved booster biocides. Unfortunately, these technologies are unproven and may not meet the demands of today's oceangoing fleet (more than 5 years of service life), 80 percent of which is coated with organotin antifouling coatings.
Copper has been the principal biocide in antifouling coatings for more than 150 years. The question is not if this is a problem, but where. Although proponents of the continued use of copper compounds as antifoulants cite the fact that copper is a naturally occurring micronutrient, there is concern about the long-term effects of copper when the concentrations from the combination of natural and anthropogenic sources greatly exceed required micronutrient levels. This Phase I research project sought to develop durable, biologically active antifouling coatings without the use of copper-based compounds or other toxicants that persist in the environment and affect nontarget species.
Novel zosteric acid analogs were identified in Phase I and used in coating formulation. Materials were blended with film-forming resins or grafted to acrylics and polymerized. Hard, durable films, with excellent adhesion to aluminum, steel, and polyester gel-coat, resulted from blending materials with epoxy and acrylate resins. Adhesion and hardness of the resulting coatings matched or exceeded that of the copper-based antifouling coating used as a comparative control, Ameron ABC#3. Surface imaging by tapping mode atomic force microscopy revealed that these coatings form nanocomposites when polymerized in situ on test surfaces. Laboratory testing with the most promising compound identified a dose-related response in cyprid settlement assays. As a result, an EC50 value of 0.205 was calculated. Initial fouling resistance (FR) results from field testing in high-fouling marine environments were promising. After 31 days of exposure in Florida waters, average FR of an epoxy-based coating with 10 percent by weight of the test material was comparable to the copper-based control, with 98 and 100 FR ratings, respectively, following ASTM D 3623. The untreated control panel rated 43 after the same period. Results from testing in New England waters were similar. After 39 days of exposure, FR of epoxy films with the test material rated 95, comparable to the copper-based control that rated 100.
Unfortunately, antifouling activity of coatings at both sites deteriorated rapidly and was not observed after 2 months of exposure. Results from field testing suggest that the biologically active moiety was available in sufficient concentrations at the coating surface after 1 month of exposure, but as the material degraded by hydrolysis, it left an insoluble layer of inert carrier resin that was readily fouled. Matching the solubility of the delivery system (resin) to the half-life and/or solubility of the bioactive material is crucial to the design of any effective antifouling coating. Unfortunately, E Paint Company's attempts to achieve this end were unsuccessful.
Copper-free coatings that are biologically active with antifouling properties were developed. Unfortunately, biological activity of these coatings is short-lived, with activity diminishing after only 1 month of exposure. Based on results from Phase I, and problems associated with synthesis of the proposed starting materials, E Paint Company does not intend to seek additional funding to support this research.