Study On The Chemical Modification Of Silk Tyrosine Residues And Its Performance

With the rapid development of economy and society,the living environment of human being has been worse and the ultraviolet radiation in sunlight reaching the earth’s surface has increased.The problems of photo degradation,such as photo yellowing,photo tendering of silk and other protein materials have appeared more obvious.Therefore,the research and development of such technology to improve the photo stability for silk fabrics have been very important and significant.In this paper,in view of the poor photo stability of silk protein,a kind of benzotriazole structure was synthesized on the side groups of silk protein using the phenol group of tyrosine residues of silk protein via chemical modification methods,and the photo stability of modified silk was investigated as well.The studies are described as the following aspects:1.The chemical modification in the formation of benzotriazole structure on tyrosine,purification of products and characterization.There were two steps in the chemical modification of tyrosine.Firstly,the diazonium salt of o-nitroaniline was prepared,which reacted with tyrosine to form coupling intermediate product in alkaline conditions.Then,the coupling intermediate product was reduced to form benzotriazole structure by the reduction of thiourea dioxide under alkaline conditions.The final product was purified with separation of column chromatography,and the purity resulted was more than 95%.Furthermore,the final modified product was also characterized using UV-visible spectroscopy,infrared spectroscopy,mass spectrometry,nuclear magnetic resonance spectroscopy,high-performance liquid chromatography,etc.2.The chemical modification in the formation of benzotriazole structure on silk tyrosine residues and the optimization of reaction condition.The optimization of chemical modification conditions were carried out in both the coupling reaction of diazonium salt and the tyrosine residues of silk protein,and the reduction to form benzotriazole structure subsequently.The optimized coupled conditions of silk were:the molar ratio of diazonium salt and tyrosine of silk fabric was 1:2/3;the pH value was about 6.8;the coupling time was 45min;the bath ratio was 1:45.Under this optimal conditions,the K/S value of silk fabric formed from coupling modification of silk was the highest.The reduction modification conditions of benzotriazole structure were:the molar ratio of tyrosine on fabric,thiourea dioxide and sodium carbonate was 1:4:10.5;the reduction temperature and time were 90 ℃ and 3.0 hours,respectively;the bath ratio was 1:60.Under this optimized conditions,the component of tyrosine modified with benzotriazole structure was the highest in the modified silk hydrolyzate.3.The dyeing properties and photo stability of silk fabrics modified with benzotriazole structure.The experimental results showed that the colour yield of silk fabrics modified with benzotriazole structure had somewhat declined with dyeing of Acid red 52R,Acid Yellow 36 and Acid Blue 83,in comparison to the untreated white silk and the hues of dyed silk fabrics were slight changed.Through the analysis of the tyrosine contents of untreated white silk and the modified silk with benzotriazole structure,and the benzotriazole structure contents of silk modified before and after UV irradiation,it was noticed that the photo stability of silk fabrics could be improved in a certain content with the modification of benzotriazole structure.On the other hand,through the testing and comparative analysis of chromatism of untreated white silk fabrics and fabric samples which had been modified with benzotriazole structure and dyed by trichromatic acid dyes before and after UV irradiation,the results indicated that the modification on silk with benzotriazole structure could have the photo stability of silk dyed with Acid red 52R hardly improved,somewhat improved with Acid Yellow 36 and improved obviously with Acid Blue 83,respectively.These results maybe related to the structure of the the dyes used and further studied will be done in the future.