Role of dye structure in improved dyeing of cotton with direct dyes in presence of a redox system and influence of glucose in improving direct dye uptake on cotton

Abstract

<span style="font-size:11.0pt;line-height:115%; font-family:" calibri","sans-serif";mso-ascii-theme-font:minor-latin;mso-fareast-font-family:="" calibri;mso-fareast-theme-font:minor-latin;mso-hansi-theme-font:minor-latin;="" mso-bidi-font-family:"times="" new="" roman";mso-ansi-language:en-us;mso-fareast-language:="" en-us;mso-bidi-language:ar-sa"="">The dyeing of a cotton fabric with direct dye in presence and absence of a redox system (potassium persulphate/ammonium persulphate as oxidant and glucose as reducing agent) as well as in presence of a reducing agent (glucose) alone has been investigated. The dyeing properties studied are dye exhaustion, colour strength and wash fastness. The results of the study indicate that improvement is dye dependent and varies with the chromophore of the dye, irrespective of the auxochrome groups. When a redox system is used, the dyeing process proceeds via a free radical mechanism and a covalent bond is formed by the reaction of dye free radical and cellulose free radical. The increased life of free radical (dye or cellulose), due to stabilization by resonance, results in increased probability of reaction and thus improvement in dyeing properties. Improvement is also observed when glucose alone is used since glucose increases the accessible regions of the fibre to dyes. The probability of dye absorption thus increases due to the interaction of dispersive forces and, to some extent, H-bonding with the cellulose substrate. The use of glucose for after treatment to improve the dye fixation is time-saving as well as economical. </span>