Mechanically robust bifunctional hydrophobic polycarbazole-decorated multiwall carbon nanotube-Pithecellobium dulce oil polyester amide nanocomposite coatings: fabrication, characterization, anticorrosive and antimicrobial studies

Abstract

The processing and application of commercial polymer coatings involving the use of organic solvents yield volatile organic compounds (VOCs), causing severe health hazards and depletion of fossil fuels, which need to be managed through stringent environmental regulations. Thus, to overcome these problems, coating technologists and researchers have put enormous efforts into developing VOC-free sustainable oleo-polymer coatings. Herein, we report the preparation of polycarbazole (PCz), PCz-enwrapped MWCNT hybrid (PCz@CNT) nanofillers and Pithecellobium dulce oil polyester amide (PDPEtA) matrix. PDPEtA and its nanocomposite (PCz–PDPEtA, CNT–PDPEtA, and PCz@CNT–PDPEtA) coatings were applied on polished CS specimens. Subsequently, their structural, thermal, morphological, and hydrophobic characteristics were analyzed through ASTM laboratory standards and other laboratory methods such as Fourier-transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and contact angle techniques. Furthermore, their corrosion protection [under saline (5 wt% NaCl) environment] abilities were investigated using PDP, EIS, and salt spray techniques. The antimicrobial and anti-biofilm activities of the coatings against P. aeruginosa, E. coli, B. subtilis, and S. aureus bacteria were investigated using the agar well diffusion method, light microscopy (LM) and confocal laser scanning microscopy (CLSM) techniques. The PCz@CNT–PDPEtA nanocomposite coating exhibited superior corrosion protective abilities (I_corr: 9.46 × 10⁻⁹ A cm⁻², E_corr: −0.0443 V, corrosion rate: 1.09 × 10⁻⁴ mpy, R_p: 1.50 × 10⁷, and η_i: 99.97) and higher antimicrobial ZOIs (14.67 ± 0.9, 15.33 ± 0.5, 15 ± 0.8, and 14.67 ± 0.9) than other similar reported coating systems. Moreover, it showed better physicochemical (acid value, refractive index, and specific-gravity), structural, superior physicomechanical (impact resistance, scratch hardness, bend test, etc.), and thermal properties.