Dyeing And Functionalization Of Silk Fiber Using Natural Polyphenols

Silk is one of the important and high grade textile fibers,and it can also be used as biomaterial.But the application of silk is restricted because of its poor antibacterial and antioxidant activities.The improvement of antibacterial and antioxidant activities can increase the added values of silk products which are conducive to expand their application scopes.Natural polyphenols are important bioactive compounds.Most of them possess multi-bioactive and multi-functions such as antibacterial,antiviral,anti-inflammatory,antioxidant,UV absorbing,deodorization,anticoagulation,anticancer,etc.Some polyphenols have high coloring power.Natural polyphenols show a good application prospect in pharmaceutical,foodstuff,biomaterial and fiber industries.In this work,three natural polyphenols,namely hematoxylin,resveratrol and chlorogenic acid,were applied to the dyeing and/or antibacterial and antioxidant functionalization of silk fiber.In addition,these three polyphenols were employed as reducing agents to prepare silver nanoparticles(AgNPs)which were used to further enhance the antibacterial ability of silk fiber.The important results and conclusions were in the following:(a)Hematoxylin,resveratrol and chlorogenic acid had good stability in weakly acidic condition,and poor stability in alkaline condition.Hematoxylin was rapidly oxidized in alkaline medium and at high temperature.The color of aqueous hematoxylin solution greatly depended on its acidity or alkalinity,and a color change easily occurred in alkaline condition.(b)Resveratrol and chlorogenic acid had no coloring power,and could not be used to dye silk fiber.After hematoxylin was oxidized to hematein in an aqueous solution,hematein could exhibit very high coloring power.Hematoxylin should be applied to the dyeing of silk at pH 6 and 80 ?,and the dyed silk had a yellow appearance.Hematoxylin exhibited a very good building-up on silk fiber.However,the dyed silk showed very poor light color fastness and very poor washing color fastness in terms of color change.The post-mordanting by ferrous,ferric and aluminium ions improved the washing color change fastness of the dyed silk,and remarkably increased the light color fastness of the dyed silk.However,post-mordanting greatly changed the color of the dyed silk.After mordanted by ferrous,ferric and aluminium ions,the dyed silk became faint blue,dull yellow,and violet,respectively.All of hematoxylin,resveratrol and chlorogenic acid imparted very good antibacterial activity to silk,and both of hematoxylin and resveratrol imparted high antioxidant activity to silk.(c)Hematoxylin,resveratrol and chlorogenic acid used as reductants could rapidly reduce silver ions into AgNPs in a weakly alkaline condition.The important factors affecting the preparation were pH,dosage of natural polyphenols,and dosage of silver ions.The average particle size of the resulting AgNPs was about tens of nanometers.The AgNPs prepared using three natural polyphenols were applied to the functionalization of silk fiber.The AgNPs treated silk fabrics displayed a yellow appearance,and much higher antibacterial activity and lower than antioxidant activity than the samples treated alone with natural polyphenols.Moreover,the antibacterial of the AgNPs treated silk fabrics exhibited good resistance to washing.(d)The in-situ fabrication of AgNPs on the surface of silk fiber in the case of the use of natural polyphenols as reductants was applied to the functional modification of silk fiber.The resulting silk fabrics showed the best and washing-resistant antibacterial activity as compared with the samples which were treated alone with natural polyphenols and modified with the AgNPs obtained using natural polyphenols.Furthermore,the in-situ fabrication of AgNPs using resveratrol and hematoxylin was able to impart good antioxidant activity to silk fiber.