Functionalization Of Silk Using Natural Flavonoids

As the rapid development of textile industry,the environmental issue is becoming more and more serious recently.Nowadays,the application of natural bioactives to textiles has been drawn an increasing interest.Through such process,the effluent generation and the dependence of non-renewable petroleum resources can be simultaneously reduced in comparison with the production process involving synthetic functional agents.Flavonoids play a significant role in the family of natural bioactives for their desirable antibacterial activity,antioxidant activity and UV protection performance etc.Moreover,simultaneous coloration and functionalization of textiles can be achieved in a single run by using natural bioactives.Silk fiber has been historically referred to as the " queen of textiles" owing to its nice appearance and excellent performance.Silk has also found a wide range of applications as a biomaterial in the medical field due to its remarkable mechanical performance,biocompatibility,and controlled degradability.Silk suffers from some shortcomings such as deterioration,yellowing and poor UV protection capability etc.,which greatly restrict its application.Currently,a few studies on the application of flavonoids to silk for coloration and functionalization purpose have already been reported.However,the adsorption mechanism of flavonoids to silk is still obscure.Some flavonoids display undesirable water solubility which exerts impact on the performance of treated silk.Thus,further investigations need to be carried out to give answers to such problems.In this study,three flavonoids(baicalin,quercetin and rutin)were adopted for silk functionalization through adsorption technique,green synthesis of silver nanoparticles(AgNPs),molecular modification for enhancing solubility and metal mordanting method.This study aims to establish a sustainable textile functionalization process through the application of flavonoids to textiles.The main conclusions are as follows:In the study of adsorption technique for multiple functional silk,we found that the quantity of the adsorption of baicalin on silk greatly depended on the pH value of treatment bath.Flavonoids displayed higher exhaustion and utilization on silk at lower pH value.The adsorption kinetics of bailcain,quercetin and rutin onto silk obeyed the pseudo-secondorder kinetic model,and the equilibrium adsorption isotherms fit well to the Langmuir adsorption mode.Baicalin or quercetin treated silk showed higher antioxidant activity,antibacterial activity and UV protection performance than rutin treated silk.At almost the same adsorption quantity,rutin imparted slightly higher antibacterial and antioxidant activity to silk due to its higher extent of desorption from silk in aqueous solution caused by its low affinity to silk.The functionalities of baicalin or rutin treated silk showed obvious reduction after first washing cycle,however,quercetin treated silk remained good functionalities even after 10 washing cycles.In terms of the AgNPs green synthesis using flavonoids,it is found that more AgNPs were produced at higher pH values.The average particle size of AgNPs decreased with increasing pH value.At pH 10,the sizes of AgNPs prepared using three flavonoids have following relationship:quercetin<rutin<baicalin.The AgNPs size decreased with increasing flavonoids concentration.The size of AgNPs prepared by baicalin and rutin decreased as the temperature rised.The measurement of zeta electrical potential indicates that the as prepared AgNPs were negatively charged.The size and zeta potential of AgNPs were stable within 30 days.As the concentration of AgNPs increased,the color saturation and lightness of silk decreased.The AgNPs treated silk showed antibacterial activity of 95%against E.coli and S.aureus.The antioxidant activity of AgNPs treated silk could be further enhanced by using higher concentration of AgNPs.The AgNPs treated silk remained antibacterial activities over 85%even after 30 washing cycles.In the study of molecular modification,quercetin and rutin were modified with a water soluble and reactive UV agent.It is found that both quercetin and rutin after modification displayed great improvement in their water solubility.Modified quercetin showed better building up property on silk than modified rutin.Silk treated with modified flavonoids displayed better color uniformity,rubbing fastness and photostability than those treated with unmodified flavonoids.Modified flavonoids treated silk has good antibacterial activity and UV protection performance,and a certain degree of antioxidant activity.After 10 washing cycles,the antibacterial activity of modified flavonoids treated silk showed a marginal decrease,however,the antioxidant activity and UV protection performance largely decreased.Multiple functional properties were imparted to silk textiles by means of the adsorption technique of bio-based flavonoids followed by mordanting with metal salts.In addition to antibacterial and antioxidant functions as well as coloration effect,a novel function of flame resistance was found for the first time.The combination treatment of flavonoids and metal salts enhanced the thermal stability of silk fiber in nitrogen,but promoted the pyrolysis of the degraded products of silk fiber at high temperatures.The desirable flame retardancy and smoke surpression of treated silk were confirmed by buring test and smoke density measurement.The treated silk fabrics had a good char forming ability during combustion as evidenced by their morphological structures of charred residues,which contributed to their enhanced flame retardancy and smoke suppression.Furthermore,such flame retardancy was durable to washing due to the complexation present among flavonoids,metal ions and silk fiber.Even after 20 washing cycles,the treated silk remained LOI values up to 27%and char lengths shorter than 15 cm,fulfilling the requirement for the char length of the B1 level.In addition,the complexation of Fe2+ and Ti4+ions with flavonoids allowed silk to be dyed into distinct colors with different hues,and saturation and lightness,indicating that the use of different metal salts and flavonoids can produce the flame retardant silk textiles with rich colors.