pH-sensitive microcapsules based on biopolymers for active corrosion protection of carbon steel at different pH

Dual-functional poly(urea-formaldehyde) microcapsules, containing the healing agent linseed oil in the core and the corrosion inhibitor benzotriazole (BTA) in the multilayer shell, were synthesized by in situ polymerization. A layer-by-layer assembly technique was applied using the biopolymers alginate and chitosan as oppositely charged polyelectrolytes. The microcapsules were characterized concerning their composition, surface charge, and morphology, using FTIR, TG, zeta potential measurements and SEM. The capsules are spherical, with an average diameter of 0.99 ± 0.15 μm. The encapsulation of linseed oil was confirmed by FTIR and TG. The adsorption of the multilayers was monitored by zeta potential measurements. The release of BTA, in a solution of NaCl and at different pH values, was studied by UV–Vis spectrophotometry, showing the stimulus-responsive behavior of the microcapsules. The corrosion protection performance was investigated by electrochemical impedance spectroscopy (EIS), using a carbon steel substrate coated with epoxy resin loaded with 5 wt% microcapsules. The EIS results showed that the presence of microcapsules provided better protection compared to the pure resin coating, with average RP three times higher. •The smart coating showed better anticorrosive effect attributed to two active agents.•The smart coating showed the best corrosion protection performance at acidic medium.•EIS demonstrated the important actuation of linseed oil on the corrosion resistance.