Sustainable dyeing of mulberry silk fabric using extracts of green tea (Camellia sinensis): Extraction, mordanting, dyed silk fabric properties and silk-dye interaction mechanism

Sustainability and environmental awareness had an impulse in increasing the global interest to utilize the industrial crops for producing new colouring shades in place of hazardous synthetic dyes. The present research focuses on extracting functional components from green tea (Camelia sinensis) leaves using water and methanol/water solvent systems and their application in the mordant dyeing of mulberry silk fabrics. The effect of pH was studied to maximize the yield of total polyphenols, flavonoids, and antioxidant properties of the solvent extracts. Compared to the unmordanted dyed silk, the mordant dyeing of silk with tea extracts at a temperature of 80 ℃ for 45 min resulted in significant improvements in various color properties. These enhancements include the shade, color strength (K/S), color coordinates, and fastness properties of the dyed silk fabric. Mordant dyeing of silk fabric enhanced UV protection and antimicrobial activities as well. The bonding properties of tea polyphenols on silk was well demonstrated with the help of X-ray photoelectron spectroscopy (XPS). To establish the mechanism of dyeing, catechin was used as a standard and mordant dyeing in silk, resulting in similar golden-yellow coloration. It shows identical properties with the silk dyed with tea extracts resulting in the fact that catechins are the responsible components in silk dyeing while using tea extracts. Theoretical interaction energy (Einteraction = −13.836 kJ/mol) calculation established good stability of mordanted catechin dyeing on silk, and catechin stability in different solvents were in the order catechin-water > catechin-methanol > catechin-ethanol. This work suggests that the mulberry silk fabrics dyed with green tea extract showed diverse color variations, which is highly promising to be used as a natural dye in the textile industry.