Nucleophilic modification of flavonoids for enhanced solubility and photostability towards uniform colouration, bio-activation and ultraviolet-proof finishing of silk fabric

This study targets on the molecular-decoration of flavonoids (FLs) with a reactive ultraviolet absorber (UV-ABS) to enhance their low-solubility and photo-sensitivity, further serving for uniform and ultraviolet (UV)-proof treatment of silk. Quercetin (QUE) and rutin (RUT) showing structural discrepancy in disaccharide moiety are compared. The chemical structures of modified flavonoids (MOD-FLs), adsorption behaviour/mechanism of MOD-FLs on silk, and the colour features and functionalities of treated silk were explored. Results reveal that the absorbance of FLs in water significantly increases after modification indicating the enhanced solubility, which is reconfirmed by the water/n-butanol phase separation experiment. Two intense adsorption bands of MOD-FLs in UVA/UVB range imply their potential use as UV-proof finisher for textile. The exhaustion of MOD-FLs on silk gradually descends as pH increases. MOD-FLs display a closer trend to Psuedo 2nd-order kinetic model than FLs indicating the dominance of chemical adsorption due to the ionic nature of UV-ABS part. MOD-QUE show superior building-up property than MOD-RUT on silk, which is beneficial to achieving diverse intensity of colour and functionality on silk. Fewer aggregates of MOD-FLs are observed on silk surface than FLs. After modification, the colour fading of QUE and RUT treated silk after 8 h light exposure significantly reduce by 71.96% and 42.91%, respectively. MOD-FLs treated silk disinfect over 80 % of E. coli and S. aureus. However, a significant antioxidant decrease of FLs occurs after modification. MOD-FLs (5% owf) imparts silk with high UPF values (50+). In general, the strategy for enhancing the water solubility and photostability of FLs is developed to better serve as bio-based modifiers for textile which is also transferable to the modification of other natural molecules.