Corrosion performance of polyurethane hybrid coatings with encapsulated inhibitor

Direct incorporation of inhibitor molecules in hybrid coatings results in premature deterioration of coatings performance. The inhibitor molecules interfere with curing of the organic coating and cause delamination due to fast leaching. This challenge is overcome in this work by encapsulating an effective organic inhibitor, 2-mercaptobenzothiazole (MBT), in polylactic acid (PLA) nanoparticles produced via nanoprecipitation method for corrosion protection of 2024-T3 aluminum alloy. The nanoparticles are designed as function of polylactic acid concentration, solvent/antisolvent volume ratio, and the PLA/MBT mass ratio. Nanoparticle size distribution, inhibitor loading percentage, and encapsulation efficiency are studied. The PLA nanoparticles with encapsulated MBT are incorporated in a polyurethane/polysiloxane hybrid coating and its properties are evaluated using impact resistance, pull-off strength, cross-hatch adhesion, pencil and pendulum hardness, and solvent resistance. The corrosion performance of the hybrid coatings is investigated by electrochemical impedance spectroscope (EIS) and potentiostatic polarization. The polyurethane/polysiloxane hybrid coating shows a 200-fold increase in corrosion induction time due to incorporation of MBT-impregnated PLA nanoparticles.