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Novel hybrid halloysite nanotubes (HHNTs) were developed and used as smart carriers for corrosion protection of steel. For this purpose, as-received halloysite nanotubes (HNTs) were loaded with a corrosion inhibitor, imidazole (IM), by vacuum encapsulation. In the next step, a layer by layer technique was employed to intercalate another inhibitor, dodecylamine (DDA), in the polyelectrolyte multilayers of polyethylenimine and sulfonated polyether ether ketone, leading to the formation of HHNTs. During this process, IM (5 wt %) was successfully encapsulated into the lumen of HNTs, while DDA (0.4 wt %) was effectively intercalated into the polyelectrolyte layers. Later, the HHNTs (3 wt %) were thoroughly dispersed into the epoxy matrix to develop smart hybrid self-healing polymeric coatings designated as hybrid coatings. For a precise evaluation, epoxy coatings containing as-received HNTs (3 wt %) without any loading denoted to as reference coatings and modified coatings containing HNTs loaded with IM-loaded HNTs (3 wt %) were also developed. A comparative analysis elucidates that the hybrid coatings demonstrate decent thermal stability, improved mechanical properties, and promising anticorrosion properties compared to the reference and modified coatings. The calculated corrosion inhibition efficiencies of the modified and hybrid coatings are 92 and 99.8%, respectively, when compared to the reference coatings. Noticeably, the superior anticorrosion properties of hybrid coatings can be attributed to the synergetic effect of both the inhibitors loaded into HHNTs and their efficient release in response to the localized pH change of the corrosive medium. Moreover, IM shows an active release in both acidic and basic media, which makes it suitable for the protection of steel at the early stages of damage, while DDA being efficiently released in the acidic medium may contribute to impeding the corrosion activity at the later stages of deterioration. The tempting properties of hybrid coatings demonstrate the beneficial role of the development of novel HHNTs and their use as smart carriers in the polymeric matrix for corrosion protection of steel.

The present research work focuses on the synthesis, characterization and properties of novel polyelectrolyte multilayered microcapsules used as smart additives in organic coatings for corrosion protection of steel parts. Urea formaldehyde microcapsules encapsulated with linalyl acetate (UFMCs), sensitive to mechanical stimulus, were synthesized by in situ emulsion polymerization technique. In the next step, dodecylamine, working as a pH stimulus corrosion inhibitor, was loaded into layers of polyelectrolyte molecules, polyethylenimine (PEI) and sulfonated polyether ether ketone (SPEEK). These were applied layer-by-layer over the microcapsules to form inhibitor containing multilayered urea formaldehyde microcapsules (MLUFMCs). In the next step, MLUFMCs (5.0 wt%) and UFMCs (5.0 wt%) were thoroughly dispersed into the epoxy resin and coated on cleaned steel. A comparison of the structural, thermal and anticorrosive properties indicates that coatings modified with multilayered capsules (PMLSCs) demonstrate good thermal stability, improved self-healing characteristics and higher corrosion resistance compared to the coating modified with urea formaldehyde microcapsules. The improved properties of PMLSCs can be attributed to efficient release of the encapsulated self-healing agent and corrosion inhibitor from the MLUFMCs. Therefore, epoxy coatings modified with the novel multilayered capsules may be attractive for corrosion protection of steel parts used in oil and gas and related industries.

Multifunctional nanocomposite coatings were synthesized by reinforcing a polymeric matrix with halloysite nanotubes (HNTs) loaded with corrosion inhibitor (NaNO3) and urea formaldehyde microcapsules (UFMCs) encapsulated with a self-healing agent (linseed oil (LO)). The developed polymeric nanocomposite coatings were applied on the polished mild steel substrate using the doctor’s blade technique. The structural (FTIR, XPS) and thermogravimetric (TGA) analyses reveal the loading of HNTs with NaNO3 and encapsulation of UFMCs with linseed oil. It was observed that self-release of the inhibitor from HNTs in response to pH change was a time dependent process. Nanocomposite coatings demonstrate decent self-healing effects in response to the external controlled mechanical damage. Electrochemical impedance spectroscopic analysis (EIS) indicates promising anticorrosive performance of novel nanocomposite coatings. Observed corrosion resistance of the developed smart coatings may be attributed to the efficient release of inhibitor and self-healing agent in response to the external stimuli. Polymeric nanocomposite coatings modified with multifunctional species may offer suitable corrosion protection of steel in the oil and gas industry.