Furthermore, natural dyeing requires skilled craftsmanship thus, it is more expensive than synthetic dyeing. For instance, it is difficult to reproduce shades by using natural dyes/colorants, as these agro-products vary from one crop season to another, place to place, species to species, maturity period, etc. However, natural dyeing technology still offers inevitable disadvantages. Therefore, dyeing of textiles using natural dyes is an effective and acceptable way to reduce pollution caused by various processes performed in the textile industry ( 8, 9). The advantages of natural dyes, including environment friendly, biodegradable, nontoxic, and nonallergenic, make them a promising substitute for synthetic dyes. Natural dyes can be effective against both gram-positive and gram-negative bacteria and can be used as eco-friendly antifungal and antibacterial agents on various textile products, exhibiting the application prospects in the field of garment manufacturing for kids and for developing health-care products and foodstuffs ( 7).

Moreover, the residual pigment after dyeing could be utilized as an ideal fertilizer in agricultural fields ( 6). In contrast, natural dyes such as lycopene, curcuma, and indigo are extracted from plants, animals, and minerals without any chemical treatment ( 5). Classical synthetic dyes are stable to light, heat, and oxidants and they are nonbiodegradable ( 3) and thus constitute the main contaminant of effluent ( 4). Textile industry uses excessive amount of water for coloring and postprocessing ( 1, 2), and the water consumption and environmental pollution have led to the requirement of severe control tendency on account of the emission of toxic and stubborn concentrated dye solution. These results can possibly promote the future use of natural dyes in the fiber produced by a spun-dyeing technique. The colorfastness to artificial light could reach grade 5, the fastness to washing with detergent reached grade 3–4, the fastness to rubbing reached grade 4–5, and that to high temperature reached grade 4–5.

The colorfastness of natural indigo spun-dyed fiber was outstanding even when mordant was not used in the production process. The fabric exhibited excellent dyeing uniformity, as indicated by the relative standard deviation of the surface color depth value on the fabric, which was no more than 2.39%.

The level dyeing property and colorfastness of the fabric were tested. The natural indigo was evenly embedded in the viscose fiber, and the results indicated the existence of a direct ratio relationship between the performance of natural indigo and the color depth of the fiber. Fabrics with different color depths were obtained by adjusting the color value and the content of indigo pigment. Herein, the natural pigment-dyed cellulose fiber was prepared by wet-spinning technique, and the microstructure of the colored fiber was comprehensively studied. To improve the level dyeing property and colorfastness of natural pigment-dyed cellulose fiber, a study on the structure and properties of natural indigo spun-dyed viscose fiber was carried out systematically.

Indigo color example