Abstract
Sodium hydrosulphite is used commercially as the reducing agent for vat dyes in the dyeing of cotton. Large amounts of sodium sulphate, sulphur oxyanion and toxic sulphite are produced during the dyeing due to the dissociation of sodium hydrosulphite leading to severe air and water pollution. This research focuses on the use of alkaline iron (II) salt as the reducing agent for vat dyeing on cotton fabrics through a complete replace¬ment of hydrosulphite. The 34 Box-Behnken design was used to achieve optimum parameters and statistically analyse the performance of the new reducing system. The results showed that the alkaline iron (II) salt system was relatively effective in developing a comparable dyebath reduction potential, surface colour strength of cotton and colourfastness, if compared to the hydrosulphite-based reducing system. The dyebath stability in the presence and absence of the dye also showed superior results compared to that of the hydrosulphite system. Hence, it can be said that a complete substitution of sodium hydrosulphite with alkaline iron (II) salt is possible.
Highlights
Dyeing cellulosic fibres with vat dyes provides excellent colourfastness properties in terms of washing, rubbing and light [1,2]
The results showed that the alkaline iron (II) salt system was relatively effective in developing a comparable dyebath reduction potential, surface colour strength of cotton and colourfastness, if compared to the hydrosulphite-based reducing system
Cotton was dyed with ten different vat dyes (1% owf) using hydrosulphite and NaOH (10 g/l each), followed by the oxidation with H2O2
Summary
Dyeing cellulosic fibres with vat dyes provides excellent colourfastness properties in terms of washing, rubbing and light [1,2]. High salt load, depletion of dissolved oxygen, problems with nasal nuisance etc [6] To overcome these problems, attempts have been made to develop alternative eco-friendly reducing systems [7]. Attempts have been made to develop alternative eco-friendly reducing systems [7] Such new systems include electrochemical reduction [8], organic reducing agents such as hydroxyacetone [9], iron (II) salt complexes [10], and natural reducing agents such as sheghar [11], orange peel extract [12] and palm wine [13]. It was found that Fe(OH) produced via the reaction of iron (II) salts with sodium hydroxide can be complexed and taken back into the solution to obtain the desired reduction potential value. Iron (II) salts along with the gluconic acid and NaOH at 60 °C, iron (II) salts in combination with the tartaric or citric acid, triethanolamine and NaOH at room temperature and alkaline enzymes are capable of generating the required reduction potential by solubilising Fe(OH) generated from iron salts [15,16,17,18,19]
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