Matcha-modified clay polyurethane coating: improving thermal, mechanical, antimicrobial, and anticorrosion performance

In this study, matcha was introduced into the structure of sodium montmorillonite (Na⁺-MMT), then these new nanoparticles (M-MMT) were added to the polyurethane (PU) and nanocomposites were prepared. The results of the M-MMT investigation by Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) confirmed the presence of matcha in the structure. The results of electrochemical impedance spectroscopy (EIS) and salt spray tests showed that the presence of M-MMT in the matrix improves corrosion resistance. The EIS results showed that nanocomposite containing 3% (by weight) of G-MMT has 6.68 × 10¹¹ Ω.cm² resistance after 70 days of immersion in the electrolyte solution, while this value was 1.62 × 10¹¹ Ω.cm² for the neat PU. Also, the effect of M-MMT on the thermal resistance was up to 52 °C. Moreover, the results obtained from tensile tests showed that the strength and elastic modulus increased up to 19 and 180 MPa, respectively. This improvement in mechanical properties is due to the fact that the polymer chains are able to penetrate into the MMT galleries and also the distribution of nanoparticles in the matrix is uniform, which makes the nanocomposite easily eliminate stress without destruction. In addition, the presence of matcha in the structure created antimicrobial properties. Matcha contains phenolic compounds that have the ability to suppress by membrane perturbation, reduction of host ligands adhesion, and neutralizing bacterial toxins. Hence, M-MMT showed inhibitory and killing effects against Streptococcus pyogenes (Gram-positive bacteria) and Klebsiella pneumonia (Gram-negative bacteria).

Graphical abstract