Current understanding of antifouling materials is that the most effective copper-free fouling control systems are low surface energy coatings, namely silicone or fluoropolymer-based systems, that minimize the adhesion strength between fouling organisms and the specialized polymer surface. For extended performance life, these coating systems must have controlled and stable surface energy and composition, elastomeric properties, and good adhesion to the substrate. Several commercial fouling release (FR) coating systems based on silicone technology are on the market; however, none meet all of the desired performance characteristics. Many lack the toughness to withstand the rigorous physical demands of the marine environment, do not sufficiently and consistently selfclean, or due to polymer restructuring or other degradation pathways, lose many of the desirable surface properties with time and exposure to the marine environment.
The objective of this project was to develop non-toxic, copper-free, environmentally benign, antifouling polymer coatings for marine applications by blending styreneethylene/ butylene-styrene (SEBS) thermoplastic elastomers with surface-active block copolymers (SABC).
The objective was accomplished by (1) determining whether polar or non-polar SABCs offer the best materials for non-fouling coatings and optimizing these materials and (2) designing and synthesizing sufficient quantities of optimized SABC to provide samples for long-term testing. To determine the most effective non-fouling surface strategy, the SABC surfaces made from block copolymers were examined with three surface types including nonpolar, but stable, semifluorinated groups; mobile perfluoroethers; and polar ethylene oxide groups. An important piece of these studies was the assessment for biofouling behavior. Finally, the robustness of these materials was evaluated using mechanical deformation and simple wear tests. Surface analysis provided molecularlevel information about surface behavior and FR. Knowledge of fundamental processes was used to reengineer surfaces for improved FR.
This project completed synthetic design and scale-up of SABCs; developed a new spray coating method for SABC deposition; prepared large test structures and performed pseudobarnacle testing and marine evaluation; completed analysis of the issues associated with coating methods; and developed new strategies for improved coating preparation. It was clear from the surface characterization, as well as pseudobarnacle adhesion testing, that further process improvements (synthesis and processing) will be necessary before these coatings become suitable for commercial application. However, the results show that through proper molecular design of these bilayer coatings, a reduction in the pseudobarnacle adhesion force is possible. The semifluorinated bilayer coatings may be an economically feasible direction toward environmentally friendly marine fouling resistance/release coatings.
This project sought to create a copper-free, multilayer polymer coating for marine applications that exceeds the current performance of FR silicone coatings. Thermoplastic elastomers are readily available to provide the necessary mechanical, coating, and adhesion properties, while the SABCs provide the surface and FR behavior. Further process improvements will be pursued in SERDP project WP-1454 (SEED Project Completed – 2003)