Indigo dyeing of cellulose electrospun nanofibrous mats

This work was aimed to color cellulose electrospun nanofibrous mats (ENMs) with synthetic indigo dyes through the process of pad dyeing. The industrial-scale dyeing procedure, which involved pre-wetting the mats, dyeing them and finally washing them off, was adopted for the study. Dyeing parameters of dyebath pH and temperature, and concentrations of sodium hydrosulphite and indigo dyes were optimized for the color yield (K/S) of the dyed mats. The dyed cellulose ENMs produced excellent K/S values up to 13 with good colorfastness properties. The cellulose ENM was also dyed with aniline-free synthetic indigo dyes for comparing the results with the conventional synthetic indigo dye. The dyeing effluents were tested for pH, TDS (Total Dissolved Solids) and COD (Chemical Oxygen Demand) contents. The dyeing effluent of aniline-free synthetic indigo dyes had considerably reduced values in comparison to the synthetic indigo dyes, i.e. 27% reduction in the TDS contents and around 16% reduction in the COD contents. Furthermore, the ATR-FTIR spectroscopic analysis confirmed successful conversion of the cellulose acetate to the cellulose polymer and the SEM analysis revealed that the morphology of the undyed and the dyed ENMs was similar. This is a scientific progress towards coloration of the nanofibers having potential application in the apparels and clothing.