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.     

Use of polymeric emeraldine salt for conductive adhesive applications

The wide range of electrical, electrochemical, and optical properties associated with Polyaniline (PANI) and its composites has made them attractive for many industrial applications. In this study, Emeraldine Salt (ES), which is a doped conducting form of PANI, was chemically prepared in situ using the oxidizing agent ammonium persulphate in the presence of aqueous HCl solution. In order to gain insight into the efficiency of electrical conduction in relation to the chemical and viscoelastic behaviors of ES in homogeneous powder and as filler in composite adhesive forms, the interrelationship between their electrical resistivity and morphology was studied. The pressure-dependent electrical conduction behavior of ES powder shows, among other factors, the dependence of electrical resistivity on the intrinsic chemical and viscoelastic properties of powders. In order to obtain electrically conductive composite adhesive forms, a nonconducting nitrocellulose solution based adhesive was filled with as-synthesized ES in the amount 30%, 40%, and 50% by volume, and the effects of filler concentration on the composite's electrical resistivity were investigated. The results of our investigation revealed a typical percolation threshold behavior with a critical concentration of approximately 30% by volume. Finally, single lap joints were made using aluminum and zinc (plated on copper) as well as silver substrates bonded using the ES filled nitrocellulose adhesive developed, and the corresponding electrical and mechanical properties of these bonded interconnections were investigated. A complex redox-reaction mechanism catalyzed by ES filler is thought to be occurring at the boundary layer between the adhesive and the substrate for conversion from semiconductor to insulator of the joints in the cases of aluminum and zinc (plated) substrates.