Synthesis and characterisation of sulphonamide (Schiff base) ligand and its copper metal complex and their efficiency in polyurethane varnish as flame retardant and antimicrobial surface coating additives

Sulphonamide compounds are present in many bioactive compounds owing to their multiple biological applications, even their metal complexes. The study reported in this paper focused on the synthesis of a sulphonamide ligand (Schiff base) and its Cu metal complex and their possible applications as antimicrobial and flame retardant additives in polyurethane formulations for surface coating application. Thus, selected divalent (Cu II) metal complex of 4-((E)-(4-hydroxy-3-((E)-(p-tolylimino)methyl) phenyl) diazenyl)-N-(5-methylisoxazol-3-yl) benzenesulphonamide was prepared and characterised using a combination of elemental analysis, Fourier Transform Infrared, Proton Nuclear Magnetic Resonance and mass spectroscopy. The prepared Schiff base ligand and its Cu metal complex were physically added to polyurethane varnish to give varnish coating formulations at a laboratory scale and then applied onto pretreated wood and steel panels using a brush. The oxygen index, Gram negative bacteria; Gram positive bacteria and fungi values obtained indicated that the polyurethane varnish that contained the prepared ligand and its Cu metal complex as additives exhibited very good flame retardant and antimicrobial properties, respectively. It was also found that the metal complex had outperformed the ligand. The physical and mechanical resistance of the coatings was also studied, in order to assess any disadvantages owing to the incorporation of the additives. It was found that the additives did not influence the flexibility, hardness and adhesion of coating films prepared using the polyurethane varnish. The gloss of the polyurethane varnish film was improved due to the incorporation of the aromatic ring into the formulation.