Flavonoids-metal salts combination: A facile and efficient route for enhancing the flame retardancy of silk

Three flavonoids (baicalin, quercetin and rutin) were applied to silk textiles by an adsorption technique followed by mordanting with two metal salts (ferrous sulfate and titanium sulfate). A novel function, i.e., flame retardancy was found for the first time to be imparted to silk. This work aimed to provide an insight into the flame retardant effect and mechanism of flavonoid-metal complexes on silk fiber. The complexation of flavonoids and metal ions was confirmed by the Fourier transform infrared analysis and by the color changes of the flavonoids-treated silk fabrics without and with mordanting. The flame retardancy, smoke suppression, and thermal behaviors of the flame retardant silk fabrics as well as the morphological structures of the charred silk generated in the vertical burning were studied. These analyses revealed that the good char formation ability of the silk fabrics prepared by combined treatment of flavonoids and metal salts contributed to the flame retardancy and smoke suppression. After repeated washing for 20 cycles, the as-prepared silk fabrics still possessed good flame retardant and antibacterial functions, and moderate antioxidant activity. The present study provides a facile approach to produce the colored and flame retardant silk textiles with antibacterial and antioxidant functions.