Hybrid Polyurethane/Polypyrrole Composite Coatings on Passivated 316L SS for Surface Protective Action against Corrosion in Saline Medium

Hybrid treatments consisting of surface modification and subsequent protective coatings have gained extensive attention among corrosion mitigation approaches for a wide variety of structural metallic materials. This study aims to review the enhancement of the corrosion protection performance of polyurethane (PU) coatings on 316L stainless steel (SS) specimens. This was achieved via a two-step strategic treatment, primarily by electrochemical passivation and subsequent deposition of PU composite coatings with the different feed ratio of synthesized polypyrrole (PPy) nanoparticles. The effect of different applied voltage on the surface features and the corrosion behavior of the passivated SS surfaces was systematically investigated using surface characterization techniques and a potentiodynamic polarization test in a NaCl solution. Surface morphological images revealed the porous structure on the passivated surface. It is inferred from the topographical surface results that homogeneous surface roughness was achieved with the applied voltage of 5 V. Infra-red spectroscopic results validate the formation of PU/PPy composite coatings and the intermolecular chemical interaction between the PU and PPy moieties. Furthermore, corrosion measurements corroborate the improved corrosion resistance of PU/30PPy coatings with higher values of charge transfer resistance, Rct (1.0869 × 107 Ω cm2), and film resistance, Rf (2.258 × 105 Ω cm2), with the lowest values of corrosion, icorr (4.7 × 10−3 µA cm−2) compared to that of the PU/Bare specimen. In conclusion, it is confirmed that the passivated surface enhances the corrosion resistance performance of PU coated SS, and this performance is further increased with the incorporation of PPy particles.