Accurate adhesion measurements of silicone-based marine coatings: an optimized pull-off method procedure

The interlayer adhesion of multilayer fouling release coating (FRC) systems is crucial for their durability and long-term performance. However, characterizing the adhesion of such systems, particularly the silicone-based topcoats, represents unique challenges due to their nonstick surface properties, low mechanical strength, and comparatively weak interlayer adhesion. Consequently, common adhesion test methods often fail to provide consistent and reliable measurements, leading industry to adopt more unconventional methods, which, however, require a high examiner expertise and do not provide quantitative adhesion values. In the present study, the well-known pull-off adhesion method was optimized for the quantitative adhesion measurements of multilayer FRC systems. Key optimizations comprised the selection of a suitable glue, the correct preparation of the test area and the bonding of the dolly, the pull-off rate, and a more accurate failure pattern assessment using digital image analysis. The reported pull-off method procedure allowed reproducible adhesion characterization and differentiation of the tested FRC systems. Additionally, changes in the adhesion properties and the weak spots due to altered overcoating intervals and seawater immersion were detected. By following the procedure and guidelines provided in this study, the pull-off method can be effectively applied as an objective and quantitative adhesion test for multilayer FRC systems.