Scientific African (Jul 2022)
Modification of cellulosic material for rapid dyeability with malachite green dye
Abstract
Chemical modification of cellulose fibre is one of the efficient ways to improve the dye uptake and increase the dyeability properties of the fibre. The challenge with dyeing cellulose fibres is poor dye uptake and unsatisfactory dye fixation. The major scope of this study is to determine the optimum dyeing conditions that will guarantee the dye fastness onto the cotton fabric. Four modifying agents (sodium chloride (NaCl), ammonium sulphate ((NH4)2SO4), hydrated sodium carbonate (Na2CO3•10H2O), and acetic acid (CH3COOH)) in aqueous form were employed in the treatment of the cotton fabrics in a slacked condition. The study examined changes in thermodynamic parameters due to dyeing modified cotton fabric with malachite green (MG) dye. The equilibrium percentage dye exhaustions (%E), which is a measure of dye uptake by the fabrics were determined prior to and post-modification of the cellulose at varying concentrations and temperatures. The optimum values of %E obtained for the modification agents viz: CH3COOH, NH4)2SO4, NaCl, and Na2CO3•10H2O were: 89.71%, 88.57%, 85.71%, and 68.70% at concentration 2% v/v and temperature of 70 °C. The%E of modified cotton fabric dyed with malachite green was optimum in acidic conditions (i.e.CH3COOH with%E of 89.71%) followed by (NH4)2SO4; 88.57%, which undergoes hydrolysis in an aqueous solution. This was then followed by NaClaq (i.e. a neutral solution) and Na2CO3•10H2O (i.e. an alkaline solution). However, all modifying agents used enhanced the dye uptake. The values of partition coefficient (K) were in the order of 1307.73 L.tkg−1, 1162.34 L.tkg−1, 899.69 L.tkg−1, and 329.23 L.tkg−1, respectively at 70 °C; while the values for standard affinities (-Δμθ) were 20,463.94 kJ.mol−1, 20,127.85 kJ.mol−1, 19,397.40 kJ.mol−1, and 16,530.65 kJ.mol−1. This implies a correlation between the equilibrium exhaustion and standard affinity of dyed modified cotton fabric. The values of entropy change (ΔSθ) are 175.53 J.mol−1K−1, 141.29 J.mol−1K−1, 148.16 J.mol−1K−1, 81.023 J.mol−1K−1 and 255.10 J.mol−1K−1 for the four modifying agents, respectively, which implies that the reaction is feasible (spontaneous) whereas ΔHθ are -39,729 kJ.mol−1, -28,144 kJ.mol−1, -31,531 kJ.mol−1, -11,669 kJ.mol−1 and -73,928 kJ.mol−1, respectively. The negative values of ΔHθ suggested that the reactions were exothermic. This study established that modifying agents on cotton fabric is one of the finest ways to improve the affinity between dye and fabric, thereby significantly reducing the time, cost, and stress required to achieve an optimal result in the dyeing process.
