Scope:

ASTM D6903-07 method covers the released rate of organic biocide from an antifouling coating exposed in substitute ocean water. Biocide release rates vary over the life of the coating system depending on the formulation and the physical and chemical properties of the environment. Analytical procedures determine the release rate of 4,5-dichloro-2-n-Octylisothiazolin-3-one (DCOIT), zinc and copper Pyrithione (ZPT and CuPT), and N-cyclopropyl-N’-(1, 1-Dimethylethyl)-6-(Methylthio)-1,3,5-triazine-2,4-diamine (CDMTD). The most strongly recommended that the relationship between laboratory release rates and actual environment inputs be taken into account to allow a more accurate approximation of the biocide release rate from antifouling coatings under real-life conditions.

Test Procedure:

ASTM D6903-07 method use four or more coated cylindrical specimens placed in a holding tank of substitute ocean water in which the levels of organic biocide and copper maintain below 100 μg L-1. Circulate the substitute ocean water through a suitable filtration system (activated carbon filter and an absorbent filter). Each specimen is placed in 1500 mL of substitute ocean water and rotated at 60 rpm for 1 hour. The concentration of the biocide release in the substitute ocean water is recorded.

Specimen size:

A nominal 2-L (1⁄2-gal) container made of an inert material, approximately 13.5 cm (5.3 in.) in diameter and 19 cm (7.5 in.) high, is fitted with three rods also made of an inert material, approximately 6 mm (nominal 1⁄4 in.) in diameter.

Data:

Calculate the release rate (μg cm-2 d-1) for each individual test cylinder.
Rcyl=(Cbiocide×V ×D)/(T ×A)
=(Cbiocide×1.5×24)/(1 ×200)
=Cbiocide×0.18 (for 200 cm² paint area)
where:
Cbiocide = concentration of biocide in substitute ocean water, μg L-1,
V = substitute ocean water volume in measuring container, L,
D = hours per day (24),
T = rotation period, h, and
A = area of paint, cm².