Ship hull protection from marine fouling organisms is essential for efficient fleet operation and energy conservation. The standard naval antifouling coatings contain copper as a toxicant. The copper leaching from these coatings represents an environmental hazard and is the subject of increasing regulations that will impact normal fleet operations.
The goal of this project was to develop non-polluting, easy fouling release hull coatings based on flexible, low surface energy polymers. In contrast to coatings which function by releasing toxicants (e.g., organotins and copper), coatings with minimally adhesive surfaces work through the physical and mechanic al properties of the polymer surface. The ultimate goal of this work is to produce polymer surfaces which will be self-cleaning at normally attainable ship speeds.
The approach took advantage of the weak adhesion of an adherent to materials that have low surface free energy. The critical technical issues included fixing the surface orientation of the molecules and flourinated side chains and determining the degree of polymer flexibility which can be achieved without sacrificing toughness and durability.
Fouling organisms employ a number of mechanisms for adhesion to solid surfaces. However, the lower the surface energy of the solid is, the weaker the adhesive bond. Previous research demonstrated that coating flexibility and other parameters also are important to achieving easy fouling release. The approach to generating the ideal surface involved binding perflourinated side chains onto a polymeric backbone to create a comb-type polymer with the desired physical and chemical parameters. Candidate backbone structures included acrylate-based copolymers polymerized from varying ratios of acrylate/methacrylate monomers, silicone polyether-urethanes, and silicone network systems
The fouling release community has recognized that an important "first" has been achieved, namely, the demonstration that fluoropolymer elastomers demonstrate fouling release. Second and third generation fluoropolymer elastomers (fluorinated oxetanes) are being developed toward the goal of "leap-frogging" silicones and providing the "ultimate" fouling release coating. Through a systematic study of surface wettability and stability in water, cure chemistry has been discovered which greatly stabilizes coatings to chemical degradation in water. Preliminary panel testing has been carried out to correlate fouling adhesion quantitatively with surface parameters measured in the laboratory. This project was completed in FY 1997.
A tough, non-polluting, easily cleaned coating would have a major impact on decreasing maintenance of energy generation facilities which utilize water from sensitive estuarine environments, including saline (e.g., Chesapeake Bay, MD, Delaware Bay, DE, San Diego Bay, CA, etc.) and Great Lake (zebra mussel) sources. Fouling release coatings would be applicable to Navy, commercial, and private sector vessels and would decrease maintenance and life-cycle costs while also decreasing the threat to non-target organisms by toxicant release coatings.