A methodology for evaluating biocide release rate, surface roughness and leach layer formation in a TBT-free, self-polishing antifouling coating

Abstract

Due to the forthcoming IMO ban on the use of tributyltin (TBT) antifouling paints, a new generation of TBT-free coatings has been developed that typically contain cuprous oxide and an organic co-biocide. Accurate and reproducible test methods are needed to evaluate the performance and environmental impact of these new coatings. This study investigated a methodology for evaluating TBT-free, AF coatings containing cuprous oxide. A commercially available AF coating underwent rotary immersion testing at 0, 0.51 and 2.05 m s⁻¹. Scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) analysis were used to assess leach layer formation, percentage cuprous oxide by weight and particle size distribution (PSD). Biocide release rates and surface roughness were also measured. An increase in rotary speed caused a spike in Cu²⁺ release rate after which the release rate stabilised to previous levels. An increase in leach layer thickness was also observed after the rotary speed increase. A model is suggested to account for the observations.

Keywords:

• Antifouling
• SEM
• EDX
• biocide release rate
• leach layer
• copper

Acknowledgements

Work was done as part of a PhD funded by NERC and the EU project ECODOCK (www. ecodock.net). The authors would also like to thank the two anonymous reviewers for their comments on this paper.