| Silk textiles are favored by people for their soft luster,soft hand as well as good wearing comfort.Moreover,silk itself is chemically modifiable and can be modified to improve the wearability of silk.However,the silk product itself has the defect of poor light stability,which hinders the wide application of silk products in textile apparel.Therefore,in order to solve the problem of poor light stability of silk,ultraviolet absorbers of benzotriazole structure containing primary amino were synthesized in this paper.Then based on the three-component Mannich reaction mechanism,it was covalently bonded to the silk fabric and the chemical modifi cation of silk protein was realized,which laid the foundation for the research on the light stability of the silk fabric.In this paper,two ultraviolet absorbers of benzotriazole structure containing primary amino were designed and synthesized by oxidation-closed-loop method and reduction-closed-loop method respectively.And the synthesized products were characterized via UV-vis,FT-IR,MS and 1HNMR,confirming that the synthesized products were in good agreement with the expected structure.The reduction-closed-loop product was selected prior as the experimental research object,and the tyrosine monomer was used as the mimetic of silk tyrosine residue and covalently bonded with experimental subjects to simulate the process of chemical modification of silk.The factors affecting the modification process were investigated by univariate analysis using the reaction rate of tyrosine participation as the standard,and the optimal process for modifying tyrosine was obtained.The optimum modification process of the tyrosine monomer is as follows:the molar ratio is 1:3 of the primary amino group-containing benzotriazole structure compound to pyruvic aldehyde,5.5 of the solution pH,reaction at 70℃ for 10 hours.The mimetic modified products were characterized by ultraviolet spectroscopy,infrared spectroscopy,mass spectrometry and nuclear magnetic resonance spectroscopy using the reaction rate of tyrosine participation as the standard,which confirmed that the structure of the modified product was consistent with the desired structure.Based on the feasibility of tyrosine modification,the silk was modified by the same modification process,and the properties of the modified silk fabric were studied.The results show that the silk fabric can be modified based on the Mannich reaction mechanism and the modified silk fabric has relatively low UV transmittance.Besides,the change rate of K/S value is the smallest before and after soaping.Simultaneously,Mannich chemically modified silk fabrics have the lowest rate of whiteness degradation and the longest time to produce yellowing.And the decrease of silk whiteness is much lower than that of the original silk after prolonging the illumination time,indicating that the silk fabrics have better light stability after chemical modification with Mannich.According to the strength loss of the silk fabric under ultraviolet irradiation for 60 hours,the protein layer on the surface of the traditionally modified silk and original silk peeled off after long-term ultraviolet irradiation,and the fiber damage was serious.The aggregation state of silk fiber modified by aldehyde-free contrast method was relatively complete,and the surface layer of silk fiber only had a weak protein layer shedding off.However,after modification by Mannich method,the morphology of silk was intact and the surface of the fiber was not damaged,indicating that the light stability of the Mannich-modified silk fabric is significantly improved. |
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