Determination of solvent induced changes in the mechanical properties of polymer coatings
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Polymer coatings are used as barrier layers to avoid or delay corrosion of a steel substrate. These organic coatings show good mechanical properties, chemical and thermal resistance and good moisture barrier qualities due to the cross-linked polymer network. Nevertheless, various environmental influences such as moisture, oxygen and/or aggressive ions can cause defects in the polymer coating and act as promotors for the corrosion processes. The aim of the study is to investigate the influence of water uptake of two commercially available polymer coatings, a basic coating without any additives and a coating with polyamide additives.
Different characterization methods are used to determine moisture uptake. Gravimetric analysis is performed to determine the water adsorption based on weighing. Scanning force microscopy (SFM) is used to measure the surface roughness and the swelling of the organic coating caused by water uptake. Additionally, nano-mechanical measurements are performed under controlled humidity with SFM because it is more likely that the coatings are exposed to high humidity. The systems used in this study are not designed for applications in which the coating is covered by water.
Both methods show that the coatings adsorb water. Gravimetric analysis shows that thin films of the organic coatings absorb proportionally more water than thicker layers. As a result corrosion of the steel substrate occurs faster. Furthermore, the water uptake of the coatings is investigated via the swelling of the layer. This becomes particularly obvious in the height increase of the polyamide particles added in the coating.