Extraction of Functional Dyes from Tea Stem Waste in Alkaline Medium and Their Application for Simultaneous Coloration and Flame Retardant and Bioactive Functionalization of Silk

The present research focused on the extraction of the functional components of tea stem waste generated in tea processing and their application for the simultaneous coloration and flame retardant and bioactive functionalization of silk. The extraction was carried out in alkaline condition, which yielded more functional dyes than those in water and 75% aqueous ethanol. The oxidative polymerization of polyphenols during the alkaline extraction resulted in the formation of macromolecular polyphenols which could impart flame retardancy to silk. The extracts exhibited the highest uptake by silk when applied at pH 3 and 90 °C using an adsorption technique and had good washing fastness on silk but poor perspiration and wet rubbing fastness. The inadequate fastness characteristics were evidently ameliorated by postmordanting with metal salts. As adequate tea stem extract was used, dyed silk exhibited good flame retardant, antibacterial, and antioxidant behaviors. Postmordanting further enhanced flame retardancy but negatively affected antibacterial and antioxidant behaviors. The inhibition of tea stem extract on silk burning was unexpectedly found for the first time. The increased charring ability of silk caused by this process was responsible for its enhanced flame retardancy. This work suggests novel approaches of the reuse tea stem waste and the simultaneous coloration and functionalization of silk.