Salt-free-multifunctional dyeing approaches for cotton and CVC fabrics with direct and reactive dyes using chitosan and keratin

Purpose Reactive and direct dyes are the most frequently used dyes for cotton fabrics. Cellulosic fibers pose a great affinity toward them. However, both dyes consume large quantities of salts for exhaustion; these electrolytes (salt) are discharged as effluents posing environmental problems and disorders in aquatic life. Therefore, this study aims to explore alternative approaches to minimize salt consumption. Design/methodology/approach For this study, the combination of chitosan and keratin, being sustainable biopolymers, are used as mordants instead of salts for the cationization of 100% cotton and chief value cotton (CVC) during dyeing with direct and reactive dyes. Color strength, exhaustion rates and color fastness to washing, rubbing and perspiration have been evaluated in this paper. In this research, keratin solution is applied on cotton and CVC (with the cotton to polyester ratio of 80%:20%) fabrics by pad-dry-cure, while chitosan solution has been applied with the exhaust method. The pretreated fabrics are dyed with both direct and reactive dyes with 2% and 4% depth of shade (DOS). The performance of the cationized fabrics with salt-free dyeing method was compared with the conventional dyeing. Findings The results of this study showed positive impact on exhaustion rates ranged from 19% to 69% of the values obtained without salt in 2% DOS and a range of 22%–47% in 4% DOS of reactive and direct dyes with treated samples. Color fastness to crocking results indicated the improvement of results by a factor of 0.5–1 after treatment and good wash fastnesses rating (4.5/5) were achieved for the chitosan-keratin treated fabrics equivalent to untreated samples. In addition, antimicrobial testing was performed on both treated and untreated fabrics of cotton and CVC. The results indicated that chitosan treated samples showed greater inhibition toward microbial activity as compared to keratin treated samples. Fourier transform infrared (FTIR) spectroscopy was used to identify the functional groups of chitosan and keratin treated fabric samples to confirm their presence. In the FTIR spectra, the chitosan was characterized by its hydroxyl, carbonyl and amide III peaks indicating the presence of chitosan and keratin was detected by the presence of primary amines. Scanning electron microscopy analysis was conducted in which it was visibly seen that the fibers have been coated with chitosan and keratin laid after being dyed. Originality/value For the first time, direct and reactive dyes are applied on chitosan and keratin-treated cotton and CVC to obtain multifunctional and eco-friendly fabrics.