Influence of Surface Topography and Curing Chemistry on Fouling-Release Performance of Self-Stratified Siloxane-Polyurethane Coatings
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Biofouling, the attachment and growth of microorganisms and aquatic animals on submerged surfaces, poses many economic and environmental challenges like increase in frictional drag, fuel consumption, and cost of maintenance of ships. Coatings containing harmful biocides, called anti-fouling (AF) coatings, are used to combat fouling. But, the biocides proved toxic to the aquatic environment, which led to replacement of AF coatings by non-toxic fouling-release (FR) coatings. FR coatings do not contain toxic biocides and allow formation of a weak bond between the surface and the organisms, which can be easily broken through light grooming or hydrodynamic forces. Current research is aimed at developing robust coatings that can exhibit similar or superior FR performance as compared to commercial FR coatings. Previously, self-stratified FR coating systems were developed using siloxane and polyurethane (SiPU) in the Webster research group. Although the SiPU coatings exhibited comparable FR performance to the commercial standards, previous experiments did not show effect of surface grooming or cleaning on the FR performance. In the first part of the work, an SiPU formulation was abraded using two different Scotch Brite pads with varying roughness. Surface analysis experiments showed retention of hydrophobicity even after abrasions. The abraded coatings were characterized for FR performance against common fouling organisms. Improvement in FR performance of the abraded coatings compared to the smooth SiPU coating and the commercial standards against macrofoulants, like barnacles, was attributed to dimensions of the features formed on the coatings after abrasions. Recent concerns regarding hazards associated with using isocyanates to make polyurethanes necessitated the need to find “safer” alternatives in FR marine applications. Therefore, novel isocyanatefree glycidyl carbamate (GC) technologies were explored as potential substitutes for regular polyurethanes to make FR marine coatings. GC resins were modified using siloxanes and polyethylene glycols to make hydrophobic and amphiphilic coatings with varying surface chemistries. The resultant coatings were characterized for mechanical properties, thermal behavior, and finally, FR performance against common fouling organisms. Although GC coatings showed subpar overall FR performance as compared to the commercial standards, GC technologies show potential for use in marine applications.
Doctor of Philosophy