Superhydrophobic Mn(II)-coordinated technical cashew nut shell liquid-based bactericidal and corrosion-resistant advanced polyurethane coatings

Abstract

A facile route has been reported to formulate mesoporous and covalently tethered superhydrophobic (160°) metal (Mn(II)) coordinated bio-polyurethane (PU) films/coatings. Technical cashew nut shell liquid-Formaldehyde (TCNSL-F) pre-polymer was used to prepare three different metal-coordinated polyurethane {Mn(II)TCNSL-F-PU20/25/30} films/coatings by using toluene diisocyanate (TDI) (20 %, 25 %, and 30 % w.r.t. polyol) as chain extender. Fourier transform infrared (FTIR) spectroscopy analyzes the chemical structures and changes in functional groups (-OH, >CO, -NCO), while X-ray diffraction (XRD) patterns reveal the amorphous nature of these films. The coordination with metal ions improves the chemical resistance, swelling ability (pH 4, 7.4, and 10), physicomechanical properties (scratch resistance (2.2 lb), impact resistance (150 lb/in.), bending (1/8 in.), adhesion, and gloss (98 GU) of the final coatings. Thermogravimetric analysis and its derivative (TGA and DTA) demonstrate the relatively high thermal stability (up to 200 ℃) and flame retardancy with a limited oxygen index value of 27.58. Optical microscopy, field emission scanning electron (FE-SEM), and transmission electron microscopy (TEM) images confirm the development of a well-patterned spherical nanostructure within the resin. The N2 adsorption/desorption studies reveal that Mn(II)TCNSL-F-PU25 has a Brunauer-Emmett-Teller surface area of 340.783 m2/g with a 3–3.2 nm pore diameter. Electrochemical impedance spectroscopy (EIS) demonstrates (3.5 wt% NaCl solution) a superior anticorrosion performance, protective capabilities, and compactness to a metal-coordinated substrate. The high impedance, solvent resistance, and low capacitance of coatings support the potential protective capabilities of the coating for the given immersion times. In addition, antibacterial activity ascertains the inhibition ability of the coordinated films against various bacterial strains i.e., E. coli, S. aureus, K. pneumonia, and B. subtilis. The formulated Mn(II)-coordinated PU has potential to become multi-functional surface-protective material.