Specialty Coatings @ MMI
Environmentally Benign Antifouling Coatings for Marine Applications
IN A NUTSHELL: A new type of antifouling coatings for application in both fresh water and marine environments has been developed at MMI utilizing dendritic polymer nanotechnology. The resulting coatings are capable of encapsulating and strongly binding electrophilic biocides in their dendritic nano-cells, where biocides retain their antifouling activity while being prevented from leaching and polluting the aquatic environment. These coatings for the first time successfully combine the best properties of non-stick and biocide-containing coatings providing an environmentally benign solution for the protection of man-made objects.
THE PROBLEM: Adhesion of aquatic organisms (including microorganisms, plants and animals, such as zebra or quagga mussels, barnacles and the like) represents the major component of biological fouling (biofouling), a highly undesirable phenomenon occurring on numerous man-made surfaces that are either submerged or in prolonged contact with fresh or sea water. Such surfaces include the hulls of boats and ships, architectural objects such as piers and shore defenses, ship ballast water tanks, components of water purification and production plants, storage containers, pipes and turbines in hydroelectric plants, as well as various objects used in transportation, fishing, underwater drilling, pearl harvesting, defense and numerous other water-based industries. Although the total cost of biofouling to governments, industry and individuals is impossible to estimate, it certainly ranges in the tens of billions of dollars since the current global market for antifouling paints for the protection of ship hulls alone is around $1 billion annually.
THE STATE OF TECHNOLOGY: The main way of antifouling protection is the application of antifouling coatings to endangered surfaces, and there are two main types of such coatings that are presently used, including: (a) antifouling paints containing dispersed biocides, such as organo-copper compounds, which kill the fouling organisms on contact, and (b) non-stick, low surface energy coatings, such as silicones or perfluorinated polymers, which create very smooth and slippery surfaces that make it more difficult for aquatic organisms to attach. However, while the former are generally more effective, they also release biocides into the surrounding water where even in concentrations of only parts per billion they have serious toxic effects on a wide range of other aquatic species, including mollusks, such as oysters and whelks, fish, vegetation and even mammals (including dolphins). Because of this, such coatings are being gradually abandoned and in many countries, including the United States, some are even legally prohibited. On the other hand, although the low surface energy coatings make it more difficult for aquatic organisms to attach, in order to be truly effective they often need added repellents that must be “unpleasant” to the fouling organisms but either completely natural, or synthetic but biodegradable, non-toxic and not dangerous in any other way.
OUR NOVELTY: Recently, we developed a completely new type of antifouling coating, combining the best of the two traditional approaches while eliminating the pollution problem by utilizing dendritic polymer-based nanotechnology. As shown in the following figure, these coatings combine two main features: (a) a 3D honeycomb-like structure consisting of regular nano-scaled dendritic cells which are capable of chemically binding and physically encapsulating guest species, such as antifouling active biocides, with (b) silicone-like low energy surfaces. In such a construction, the encapsulated antifoulants are positioned right at the outside coating surface (within nanometer thin layers from the water interface) and are fully capable of exerting their activity across the interface to effectively repel aquatic nuisance organisms. However, they are also firmly bound (i.e., chemically complexed)and physically entrapped (i.e., sterically hindered) inside the highly branched dendritic nano-cells, so that they remain fixed in place within the coating structure and not able to migrate across the interface into the surrounding water. As a consequence, these unique dendritic polymer nano-structured coatings provide effective antifouling protection without pollution of the environment and they do so by employing proven antifouling agents in combination with smooth, non-stick silicone-based surfaces. This is the first type of coating that has this unique combination of the most desirable properties for antifouling applications.