Synthesis and assessment of novel anticorrosive polyurethane coatings containing an amine-functionalized nanoclay additive prepared by the cathodic electrophoretic deposition method

Abstract

Cathodic electrophoretic deposition (CEPD) was utilized to cover a mild steel cathode in an aqueous solution consisting of a newly synthesized two-component one-pack waterborne polyurethane resin. The resin mixture was composed of a hydroxyl terminated polyurethane prepolymer and a blocked isocyanate cross-linker, both contain build-in tertiary amine groups to provide the condition for formation of quaternary ammonium centers under acidic pH. Thermal treatment of the electrodeposited components led to formation of crosslinked polyurethane coatings with high gel content (80%). The coating was also modified by incorporation of a clay additive. For this purpose, Cloisite 30B, a quaternary ammonium modified clay was surface modified with (3-aminopropyl)trimethoxysilane and co-electrodeposited with base polyurethane components under optimized condition. All of the prepared coatings showed promising physico-mechanical properties including very good adhesion to the mild steel surface, excellent flexibility, high impact resistance as well as high pendulum hardness. Evaluation of the corrosion inhibition properties of the coatings with and without co-electrodeposited clay nanoparticles by the Electrochemical Impedance Spectroscopy (EIS) method revealed good corrosion protection of neat polyurethane coatings when exposed to 3.5% NaCl solution for 7 days. EIS assessment on the nanocomposite coating containing 0.5 wt% of modified clay showed corrosion resistance up to 8 GΩ after 2 h immersion in NaCl 3.5%. The time needed for the failing of the coating resistance was extended to 17 days for this sample. Also, results of the salt spray test revealed a lower sign of corrosion on the mild steel plate coated with the nanocomposite sample during 17 day exposure to NaCl 5% fog.