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Environmental Research Background What's New


Background:
Introduction
TBT Paint Types
Definitions
Environmental Research:
Introduction
Marine Mammals
Sea Otters
Sea Birds
Seafood
Endocrine Effects
Analytical
References

Types Of Tributyltin Paints

Tributyltin Free Association Paints
Historically, tributyltin (TBT)-free association paints were used. Free association paints are where the active ingredients are dispersed in a resinous matrix and from which they can slowly ‘leach’. This type of paint system has been the basis of most traditional antifouling paints, which have been in use since the last century. It is difficult to control the rate of release of biocides from a free association paint system so as to provide a constant leaching level. Paints containing freely associated biocides such as copper compounds and TBT, can give rise to high initial concentrations of biocides in the marine environment.

Free Association Paint Diagram

TBT Self Polishing Copolymer Paints
TBT self polishing copolymer (SPC) paints are currently used. Copolymer systems are based on a combination of biologically active resins and other active ingredients, typically TBT copolymer resins and copper compounds. The TBT biocide is chemically bonded within and throughout a copolymer resin system. The coating on a ship that has been painted with a TBT-SPC paint system will react, by hydrolysis with sea water, resulting in the slow release of TBT which combats fouling. The remaining surface of the paint system is mechanically weak and is eroded by moving seawater, resulting in the exposure of a fresh surface of TBT polymer.

Self Polishing Copolymer System diagram

This hydrolysis/erosion process is repeated until no paint is left on the surface and all of the triorganotin biocide is exhausted. The hydrolysis/erosion process confers two key properties on TBT copolymer paint system:

  • The ability to control/regulate biocide leaching rate
  • The erosion process results in ‘smoother’ surfaces, that is that the paint polishes - i.e., self-polishing copolymer or "SPC" antifoulings.


Figures reproduced from Bennett, R.F. 1996. Industrial manufacture and applications of tributyltin compounds. In: Tributyltin: Case Study of an Environmental Contaminant, editor S.J. de Mora. Cambridge University Press, Cambridge, 21 - 61 pp.



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