Ejargew Abebe and Gemeda Gebino Gelebo
For dyeing the cotton fabric with vat dyes, first it is required to reduce the dye using reducing agents. The reduction potential of reducing agent has to be matched with the dye for proper dyeing. Otherwise the problem of over reduction and under reduction may arise and leads to the change in shade. In conventional vat dyeing process, the vat dye is dissolved using hydrose, which is a powerful reducing agent followed by solubilizing with sodium hydroxide. This process creates very high pollution problem. In this study, an attempt has been made to replace hydrose by ferrous sulphate and hydrose combination as reducing agent on cotton fabric dyeing with vat dye and the results are compared with those of the treatment with conventional hydrose in terms of depth of shade, color fastness, color difference, tensile strength and effluent parameters. Among the ferrous sulphate + Hydrose combinations, 0.5g/L (10%) ferrous sulphate + 4.5g/L (90%) hydrose and 2g/L (40%) ferrous sulphate + 3g/L (60%) hydrose combinations as reducing agents give very good dyeing effect on the dyed cotton fabric with Bezathren Blue RS and Red LGG vat dyes respectively. These ferrous sulphate + hydrose combinations as reducing agents results higher color strength, lower BOD and COD values and higher fabric strength than hydrose. Therefore, hydrose can be replaced by ferrous sulphate + hydrose combinations depending on the reduction potential of a dye and by controlling the NaOH amount during dyeing.
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