Performance of polymer blends on phosphated steel substrate

Polymer blends are used to protect mild steel structures from corrosive environment. Multi-coat protective coating systems are substituted by single coat polymer blend, which will protect the surface equally for long duration when compared to the multi-coat system. In our studies, we have prepared three polymer blends, viz. silicone-acrylic, silicone-titanate and epoxy-acrylic blends. These polymer blends are applied over sandblasted as well as phosphated mild steel panels by brush. The mechanical properties like hardness and adhesion of these blends are measured and found that nearly 2 Vickers Pyramid Number (VPN) has been increased for phosphate surface. The accelerated salt spray chamber exposure also confirms that the phosphate gives additional protection to the steel substrate. The electrochemical impedance spectroscopy measurements are carried out periodically for all the three blends for 7 days. The impedance observation of acrylic silicone and silicone titanate blends on phosphate surface gives resistance values above 106 Ω cm2 after 7 days, whereas the same blends on sand blasted surface exerted resistance values below 106 Ω cm2 after the same duration, the epoxy acrylic blends are found to give resistance values above 109 Ω cm2 irrespective of the surface modification. Thus, this study concludes that the polymer blends of organic to organic binders protect the phosphate steel surface for longer duration than that of the blend composed of organic and inorganic system.