Condensed tannin from Dioscorea cirrhosa tuber as an eco-friendly and durable flame retardant for silk textile

Condensed tannin derived from Dioscorea cirrhosa tuber was employed as a novel and eco-friendly flame retardant agent for enhancing the thermal shielding and flame retardant properties of silk textile. A facile adsorption technique of condensed tannin in the weakly acidic condition was able to impart good and durable flame retardancy to silk fabric. In the treatment process, the adsorption, diffusion and deposition of condensed tannin onto silk fiber took place. The flame retardancy was demonstrated by limiting oxygen index, vertical burning and pyrolysis combustion flow calorimetry tests. The treated fabric exhibited the limiting oxygen index above 27% and the char length below 12 cm even after 20 washing cycles. The thermogravimetric analyses of the treated fabric and the morphological studies of the burned fabric residue suggested that a significant condensed-phase mechanism contributed to the improvement in the flame retardancy of silk fabric. In addition to flame retardancy, antibacterial and antioxidant activities were imparted to silk fabric. Such multifunctional properties provided by condensed tannin can expand the application of flame retardant silk. The present research indicates that condensed tannin is a promising alternative to traditional flame retardants for the finishing of silk textile.