Improving the Protection Performance of Waterborne Coatings with a Corrosion Inhibitor Encapsulated in Polyaniline-Modified Halloysite Nanotubes

Abstract

Organic coatings provide an effective way to improve the corrosion resistance of metals. Traditional organic varnishes, however, either contain highly polluting or toxic components or lack self-healing ability. In this article, we report a feasible method of preparing polyaniline-modified halloysite nanotubes (PANI@HNTs). They were loaded with a corrosion inhibitor, benzotriazole (BTA), and were tested as multifunctional anticorrosion additives for environmentally friendly epoxy waterborne coatings. The PANI@HNTs were formed via the in situ polymerization of aniline in the presence of halloysites. The BTA loading was then carried out and reached up to 14.5 wt.%. The BTA retention ability of the PANI@HNTs was significantly improved in comparison to that of pure HNT. Electrochemical impedance spectroscopy (EIS) tests of the coatings immersed in a 3.5 wt.% NaCl solution showed that the barrier and corrosion inhibition effects were enhanced by two to four orders of magnitude with the incorporation of BTA-loaded PANI@HNTs. The salt spray tests on artificially scratched coatings revealed that the surfaces protected by varnishes doped with the BTA-loaded PANI@HNTs exhibited the lowest degree of corrosion compared to the control samples, illustrating the self-healing potential of the modified coatings.

Corrosion Protection of Q235 Steel Using Epoxy Coatings Based on Polyaniline Loaded with Benzotriazole

“…BTA forms a thin protective film on the substrate beneath the coating, preventing the undamaged area from being damaged [73]. The formation mechanism of BTA forming complex is shown in Equations ( 3) and (4) [29].…”

“…These hydrogen ions are then adsorbed on the surface of the complex or combined to form meteorological hydrogen molecules [74]. In addition to the formation of complex [BTA-Fe-BTA] n , another protective mechanism of BTA is that BTA migrates to the substrate surface and reacts with Fe to form a protective layer, blocking the channel of water diffusion [29].…”

“…Vimalanandan [28] proposed a conducting polymer-based nanocapsule system, which comprises a redox-sensitive PANI shell decorated with gold nanoparticles and a self-healing agent encapsulated in the core. Liu [29] reported PANI-modified halloysite nanotubes to load the inhibitor BTA. Hao [30] obtained a mesoporous PANI hollow sphere and the corrosion inhibitor entered the cavity of hollow sphere through the large pores of the mesoporous PANI.…”

Enzymes in “Green” Synthetic Chemistry: Laccase and Lipase

“…Biopolymers—chitosan [ 43 ], collagen [ 44 ], and cellulose [ 45 ]—and magnetic particles [ 46 ] have also been used. Halloysite nanotubes/polymer combinations, often used in protective coatings [ 47 , 48 ], have been increasingly evaluated as solid enzyme scaffolds [ 49 , 50 ]. The covalent immobilization of enzymes to solid supports is most favorable for costly enzymes due to the stability and enzyme retention it facilitates.…”