Sustainable Laboratory- and Pilot-Scale Dyeing and Antimicrobial Finishing of Polyamide 66 Fabrics Using Pyrazolone-Based Metal-Complex Dyes

Abstract Two pyrazolone metal-complex dyes of the general formula [M(L)(H 2 O)]· x H 2 O (where M = Zn(II), x = 0, or Ni(II), x = 2; and H 2 ₂L = 3-methyl-5-oxo-4-(phenylhydrazono)-4,5-dihydropyrazole-1-carbothioic acid amide) were successfully synthesized. The prepared complexes were characterized by FTIR, 1 H-NMR, and UV–visible spectroscopy, as well as elemental analysis, mass spectrometry, and thermogravimetric analysis. The combined results indicate that the H 2 L ligand coordinates in a di-anionic bidentate manner through the azo nitrogen and enolic oxygen atoms after deprotonation. However, a coordinated water molecule occupies an additional coordination site, resulting in a tetrahedral geometry around the metal (II) center in both complexes. Polyamide 66 fabrics were dyed using both the ligand and zinc metal dyestuff under supercritical carbon dioxide. However, nickel exhibits negligible solubility in supercritical carbon dioxide. The dyeing process was studied under varying conditions: The temperature ranged from 100 to 120 °C, the pressure ranged from 15 to 25 MPa, and the dyeing time ranged from 1 to 2 h. A pilot-scale experiment was conducted using the prepared dyestuff, demonstrating its potential for large-scale application on polyamide 66 fabric. The color uptake, expressed as color strength ( K / S ), was assessed, and the values obtained showed that the dyed polyamide 66 fabrics were significantly better. The color fastness properties of all the dyed fabrics were evaluated, yielding good results that demonstrated durability after 10 washing cycles. A notable enhancement in antimicrobial activity has been detected for both novel dyes and dyed fabrics. The results obtained in this study highlight the potential of metal-based dyes in supercritical laboratory- and pilot-scale dyeing of polyamide 66 fabric, highlighting the feasibility of scaling up the process.