Poly(2,5-dimethoxy aniline)/fluoropolymer blend coatings to corrosion inhibition on stainless steel

Heterogeneous blends of a soluble substituted polyaniline, poly(2,5-dimethoxy aniline) (PDMA), and two fluoropolymers, poly(vinylidene fluoride) and poly(tetrafluoroethylene-co-vinylidene fluoride-co-propylene) were prepared by casting. The use of this ternary system allowed the compatibilization of the polymer mixture and the improvement of the adhesion to the substrate of stainless steel. Three compositions with increase content of PDMA were investigated and compared with PDMA coating behavior. The superficial composition of the coatings was characterized by wide-scan X-ray photoelectron spectroscopy, which indicated that the steel surface is totally covered by the polymers. Chronopotentiometry at zero current systematic study was used to determine the open circuit potential (OCP). After 7 days immersion in saline solution, PDMA and the three blends showed similar OCP values of −170 mV (reduced state), which is shifted to more positive values in relation to the bare steel. Electrochemical impedance spectroscopy was used to characterize the polymeric coatings in the absence of active corrosion at the metal/coating interface. The blends showed higher Rct compared to PDMA (102–103 times) and this result was interpreted as a contribution of barrier of fluoropolymers. Salt spray test was used to evaluate the corrosive resistance of coatings and blends in aggressive conditions during 1000 h. Energy dispersive spectrometer semi-quantitative chemical analysis was performed on the coatings after the test and indicated that blends show superior resistance to the fog test in relation to the PDMA coating. Therefore, the blends PDMA/fluoropolymer behave as an electrochemical barrier as well as a physical barrier showing superior corrosion inhibition in relation to PDMA.