RIASSUNTO
ABSTRACT
Self-polishing coatings (SPC) are widely being used in marine structures to protect metals from fouling. After restrictions on using toxic metals, coating industry are seeking environmentally-friendly SPC coatings that maintain their performance over extended periods. Unfortunately, most of the commercial SPC coatings contain different toxic materials, besides their performance is inadequate to prevent fouling under adverse conditions. The main mechanism of SPC coating is to facilitate the continuous renewal of the surface and the release of active compound via a hydrolysis reaction or an ion exchange reaction with seawater. In this study, polyurethane (PU) SPC coatings were synthesized by in-situ polymerization using biodegradable polyol. The polishing rate of coating was determined from the reduction in dry film thickness after artificial seawater immersion under a dynamic condition. The fouling resistance of coatings was considered after certain interval.
INTRODUCTION
Most of the marine coatings are prepared using toxic solvents, inhibitors, biocides and pigments. The harmful impact of VOC has led to substitution of solvent-borne coatings by waterborne coatings. It has been already proved that the biocides are excellent protecting agents when used properly in coatings. But it is also true that the effectiveness of biocides in coatings also depends on the overall synthesis criteria, the interaction between the doped biocide and coating matrices as well as the final deposited coating (thickness, adhesion, hydrophobicity, etc.) on substrates. Excess amount of biocide has detrimental effect on overall coating properties. The most important is to continuously leaching of biocide during whole coating life cycle.1–3
Epoxy and acrylate coatings are dominant in marine coating. Recently, polyurethane (PU) coatings have also attracted attention in antifouling coating due to super mechanical strength, good barrier resistance and hydrophobic properties.4–6 PU is composed of polyol (called soft segment) and diisocyanate (called hard segment). The soft segment contributes to the elastomeric properties, and the hard segment controls the coating's mechanical properties. A proper stoichiometric balance of monomers can make a long lasting coating.4–5