RECENT ADVANCES IN CATIONIC AQUEOUS EPOXY NANOCOMPOSITIONS CONTAINING ALUMINA AND TH EIR ELECTRODEPOSITION

Presently the researchers have focussed their attention on polymer nano-composites that show enhanced physico-mechanical and electrical properties compared to their conventional polymer composite counterparts. Electrophoretic deposition (EPD) of organic polymers and composite coatings on metal substrates is an important technique that finds wide application in industry. The process in essence involves application of DC voltage between the conducting anode and cathode suspended in the polyelectrolyte emulsion resulting in the electrodeposition of the polymer composite coating on theelectrode.This paper deals with the conversion of bifunctional epoxide resin into a water dispersible cationic emulsion, dispersion of nanoparticles, alumina powder and cathodic EPD of these nano composite coatings for application as dielectric and corrosion resistant coatings. Epoxy resin is chemically modified by reacting with a secondary amine to obtain an epoxy-amine adduct. The process was monitored by observing exotherm and the rise in epoxy equivalent weight using the standard volumetric method and supported by FTIR spectroscopy. IR spectrum of the adduct shows a very weak or nearly absence of typical absorption band of epoxy group at 914 cm-1 and appearance of sharp bands of tertiary amino group at 1361 and 1379 cm-1 . Neutralisation of adduct with an acid results in the formation of quaternary ammonium salt that disperses in water forming a stable cationic emulsion at a pH of 6.0 - 6.5. conventional Alumina and Natural montmorillonite (MMT) nanoclay was incorporated in aqueous epoxy emulsion using ultrasonication at 20 kHz to ensure intercalation of polymer in between the nanoclay platelets. Adherent nanocoatings were electrodeposited on Copper metal cathode and were rinsed, dried and cured at 150°C. Effect of bath parameters viz., resin content, Alumina content, nanoclay content, pH, conductivity, and the deposition parameters viz., dc voltage, interelectrode spacing and voltage application time were studied. The neat epoxy coatingand Epoxy clay alumina coatingss SEM and XRD analysis confirmed the nanostructure of the clay particles in the composite. Salt fog Corrosion resistance of EPD epoxy Alumina-MMT nanocoatings is superior to neat epoxy coating.Epoxy- Resin content of the bath emulsion studied in the range 6 – 16% by weight, have direct impact on the mass of the deposited coating or thickness. MMT nanoclay content were varied from 3 to 7% by weight of resin, Alumina from 2 to 8%. beyond which it posed processing difficulty due to viscosity rise after ultrasonication. Thermogravimetric analysis (TGA) of the cured coating in air has shown thermal stability upto 175°C when the weight loss due to decomposition begins. There is remarkable increase in electrical strength of the cured nanocoatings i.e. 29 kV/mm at 5% MMT by wt., against 18 kV/mm for neat epoxy coating. There is a improvement in impact strength of the epoxy alumina -MMT coating than pure epoxy coating.