Enzyme-based Antifouling Coatings
Chemical Product Design and Engineering (CPD&E)
Chemical Product Design & Engineering - I (CPD&E - 1)
Keywords: Antifouling, paints, coatings, enzymes
The accumulation of polymers and living species (i.e. fouling) on seawater-immersed constructions is connected with a variety of problems. On ship hulls, increased fuel consumption, due to higher drag resistance is the major problem, but promotion of corrosion, and the potential of introducing foreign species to new habitats are also of concern. Fouling has been fought for thousands of years, and the means, with which antifouling has been undertaken, have been plentiful and diverse [1]. Recently environmental considerations forced paint manufacturers to discard the more toxic of the compounds utilized. The primary substitute, cuprous oxide has a long residence time in seawater, and is therefore prone to bioaccumulation. In the near future, antifouling coatings based on controlled release of short-lived antifouling agents are likely to be introduced.
Enzymes are in general easily degradable proteins; therefore they can presumably be added to antifouling paints without harmful environmental consequences. They can be applied as antifouling agents either directly, meaning that the enzymes are used as a substitute to biocides; or indirectly, describing the use of enzymes to generate biocides in-situ.
Hydrogen peroxide is reported to have inhibiting effect on fouling organisms [2]. Its lifetime in seawater is however short, as it decompose to water and oxygen. The instability and high seawater solubility makes it virtually inapplicable in antifouling coatings as a common biocide. Application of hydrogen peroxide as antifouling agent can come about by production of the compound in-situ. Several enzymatic reactions produce hydrogen peroxide [3]. Some of these enzymes are found in the marine environment, where they are believed to contribute to antifouling properties of algae [4]. Hexose oxidase (HOx) oxidises hexose sugars under release of hydrogen peroxide.
The substrate as well as the enzyme must come from the coating, and as hexose sugars are water soluble, they are expected to leach from the coating rapidly, leaving the enzyme with no substrate. Therefore also the sugar must be produced in-situ. Amyloglucosidase (AMG) hydrolyses the water insoluble starch molecule to yield glucose.
The incorporation of enzymes into antifouling paints posses certain challenges. The enzymes must be stable in organic solvent, robust in the solvent free coating film, and have a controlled activity once activated. Making the enzyme compatible with paint is therefore one of the major challenges in developing an enzyme based antifouling paint. It can be done by a variety of known biotechnological methods (e.g. encapsulation, covalent immobilisation, etc.). Loss of enzyme activity during operation of the coating must be compensated by exposure of fresh coating layers (i.e. polishing) during operation. Polishing can be achieved by selection of coating constituents based on mathematical modelling [5]. This paper describes the obstacles when formulating an antifouling coating based on the activity of enzymes as antifoulants.
[1] D. M. Yebra, S. Kiil, K. Dam-Johansen, Progress in Organic Coatings (50). 2003. pp. 75-104.
[2] S. Ikuta, S. Ichikawa, Y. Wakao, K. Nishimura, T. Yasunaga, the American Society of Mechanical Engineers. 1988
[3] I. Schneider, K. Allermann, United States Patent Appication Publication, US2005/0147579A1
[4] C. H. Poulsen, K. M. Kragh, United States Patent Application Publication, US2002/0106361A1
[5] S. Kiil, K. Dam-Johansen, C. E. Weinell, M. S. Pedersen, Progress in organic coatings (45). 2002. pp 423-434.
Presented Wednesday 19, 12:26 to 12:45, in session Chemical Product Design & Engineering - I (CPD&E - 1).
