Corrosion restraint synergism evaluation of polyurethane duplex coating system: A case study for various anthropogenic and metropolitan sites of Karachi city

A polyurethane duplex coating system (electrogalvanized mild steel/etch primer/epoxy-polyamide primer/polyurethane topcoat system) was studied to ascertain preservation of electrogalvanized mild steel (egms) at various anthropogenic and metropolitan sites of karachi city while accelerated salt spray test was also carried out for reference. performance of coating system was examined by visual morphological inspection,gloss measurements,scanning electron microscopy (sem),energy dispersive x-ray (edx) analysis,fourier transform infrared (ftir) spectroscopy and by oxygen-carbon ratio techniques. measured data was statistically analyzed through principal component analysis and explained a variance of 99.59% when two components were considered. sem micrographs have depicted that anthropogenic and metropolitan sites testing had induced sever depletion of coating surface features as compared to accelerated salt spray testing which may be probably due to the salt-laden winds of karachi coastal city and corrosive constituents incorporated in atmospheres from industrial and automobiles exhaust. these results were also coinciding with other findings of edx and ftir spectroscopy techniques. comparison of these results on egms with our previous study of polyurethane coating system applied on mild steel,revealed earlier photodegradation of the polyurethane coating systems applied on mild steel in anthropogenic sites exposure testing i.e. oxygen/carbon ratios were higher for the coating systems applied on mild steel as established by energy dispersive x-ray analysis. © 2015,chemical society of pakistan. all rights reserved.