Semiconductive polyaniline melamine–formaldehyde blend electronic barrier to corrosion

Abstract

Polyaniline (PANI) is one of the intrinsic semiconductive polymers and shows some useful properties: high conductivity, transparency for the red and violet domain of spectrum, good elasticity and processability, superficial tension and chemical, photochemical and electrochemical behaviour. A PANI primer coat has been developed to act as an active electronic barrier to corrosion. When overlaid with a conventional durable topcoat, the coating has been shown to protect steel against salt, pollutants and other harsh environments.

Dry blends were prepared by blending the powders of doped PANI and the host polymer, a commercial melamine–formaldehyde resin AZAMIN M514 in a mixer. The hardness, elasticity, resistance and protective behaviour of melamine–formaldehyde resin films were determined. The protective behaviour of obtained melamine–formaldehyde resin blend was evaluated from quantity of Fe (II) released by the coated carbon steel samples (exposed area 1·0 cm^–2) immersed for 1 month in 50 mL 3·5%NaCl solutions. The prepared coatings protect substrate from corrosion by stabilising the oxide layer formed on the metal surface and thus prevent the metal dissolution process. An optimum formulation of melamine–formaldehyde resin coatings with 5 wt-% doped PANI exhibits good protective behaviour.