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Sulphur dyes are the most highly consumed colourants for cellulosic substrates owing to their reasonable cost and acceptable fastness. However, the use of noxious conventional reducing agent, sodium sulphide and impaired wash fastness against oxidative bleaching is gradually decreasing the market of these dyes. As the need for “Green” goods and services is raising public awareness, this paper aims to use a glucose-based biodegradable reducing agent in place of sodium sulphide to dye cotton fabrics with a range of commercial sulphur dyes. The study also proposes an aftertreatment method to improve the fastness properties of the dyeing.

The paper investigated the impact of a newly developed aftertreatment method on the fastness properties of dyeing. This involved the sequential application of a cationic fixing agent (Tinofix ECO) and tannin (Bayprotect CL) on the coloured fabrics and subsequent evaluation of colour strength, washing, light and rubbing fastness.

The effect of aftertreating the dyed cotton was found to significantly improve the light and wet rub fastness. The surface morphology of the dyeing remained unaffected as depicted by the absence of any finish residues.

The protective effect of the cation–tannin aftertreatments was examined with a view to providing the necessary commercial performance; however, it was established that the dry rub fastness was either reduced or remained unaffected and the wash fastness to International Organization for Standardization 105 C09 was also marginal.

This finishing technique is novel and can be found useful for manufacturing sulphur-dyed products with the improved light and wet rub fastness.

Sulphur dyes provide an inexpensive medium to dye cellulosic fibres with heavy shade depths. They offer moderate to good fastness to light and wet treatments. However, owing to the environmental hazard produced by the use of sodium sulphide, the practical implication of these dyes is steadily decreasing. Moreover, these dyes are prone to oxidation causing pronounced fading on exposure to laundering. This paper aims to present the green processing of sulphur dyes by using a biodegradable reducing agent in place of sodium sulphide to dye cotton fabrics. The study also proposes after-treatments with tannin to improve the fastness properties of the dyeings.

In this study, dyeings were produced on cotton fabric with a range of C.I. Leuco Sulphur dyes, which were reduced with sodium sulphide and glucose. Sulphur dyeings were after-treated with an environment-friendly tannin-based product (Bayprotect CL (BP)); subsequently, the after-treated samples were evaluated for colour strength, wash, light and rubbing fastness.

A novel after-treatment method was developed, which substantially improved the wash fastness of C.I. Leuco Sulphur Black 1 dyeing to ISO 105 C06/C09 washing. However, the degree of this improvement varied for the other sulphur dyes used. The surface morphology and the possible mechanisms for the improved fastness properties were also discussed.

The effect of after-treatment was significant for improving the wash fastness of sulphur black dyeings in particular, while the effect on other colours was minor. Significant improvements were observed for light and wet rub fastness for most of the dyeings, which signifies the importance of tannins as a finishing agent.

It is observed that the tannin-based product, BP, is found to provide the photoprotective effect by improving the lightfastness of the dyeings. Future research may involve the exploration of various tannins as a finishing agent to sulphur dyeings.

This novel finishing technique is found significant for improving the wash fastness of sulphur black 1 dyeings for both the reducing systems. Improvements were also observed for light and wet rub fastnesses for most of the dyeings.