| Silk is a natural protein fiber, which has been known as the"queen of fibers"for its good luster, soft, warmth and wearing comfort. However, due to the characteristics of its poor lightfastness, silk easily prone to aging in the using process so that seriously affect its service life. Ultraviolet radiation in sunlight is one of the main factors which are causing silk aging. To reveal the ultraviolet aging characteristics and mechanisms of silk, this thesis selected B.mori silk fabrics as the main experimental research objects. B.mori silk fabrics are plain habutai and crepe de chine. They are treated by using between outdoor natural aging experiment and indoor artificial accelerated ultraviolet aging experiment. Then this thesis analyzes the structure and properties of B.mori silk by ultraviolet irradiation aging. At the same time, it also establishes the correlation between outdoor natural aging experiment and indoor artificial accelerated ultraviolet aging experiment. In addition, it predicts the mechanical properties of B.mori silk fabric in the outdoor natural aging process as well.Through outdoor natural aging experiment and indoor artificial accelerated ultraviolet aging experiment, B.mori silk samples are treated by ultraviolet irradiation. In the ultraviolet aging process, aging factors include time, ultraviolet irradiance intensity, acidic artificial perspiration, alkaline artificial sweat and oxygen etc. This thesis systematically researches structure and properties of B.mori silk fabric from fabric appearance, color, luster, yellowness, ultraviolet protection factor UPF values, mechanical properties, chemical structure of B.mori silk, thermal analysis and amino acid analysis etc.The results show that: with ultraviolet aging time going on, whiteness values and luster of fabric surface decrease. When the natural aging time was 150d, whiteness value and contrast gloss value respectively decreased about 60% and 70%. As far as yellowing of B.mori silk fabric surface is concerned, this thesis introduces the concept of yellowness index. Yellowness index shows a trend of slow growth in the ultraviolet irradiation aging process. The mechanical test shows that breaking strength of B.mori silk fabric losses up to 90% at the natural aging time 150d. At the same time, the mechanical properties of B.mori silk fabric are affected by environmental factors as follows: alkaline > acid, summer ultraviolet irradiance intensity > spring ultraviolet irradiance intensity and oxygen > nitrogen. The FTIR test finds that silk infrared absorption peak amideⅠandⅡintensity reduces, meanwhile, crystallinity of B.mori silk increases in the ultraviolet aging process. The conformation of B.mori silk doesn't significantly change. The thermal analysis demonstrates that the endothermic peak appear at 270℃～350℃and the loss rate of weight is up to 60%～70% in the decomposition process. From amino acid analysis, in the ultraviolet aging process amino acid contents decrease. The content of tyrosine, histidine and lysine respectively reduces 75.21%, 96.74% and 53.52%. In addition, amino acid contents of B.mori silk are affected by environmental factors as follows: alkaline > acid etc.With B.mori silk fabrics including plain habutai and crepe de chine as the experimental research objects, using curvilinear regression analysis method, this thesis analyzes the correlation between outdoor natural aging experiment and indoor artificial accelerated ultraviolet aging experiment from three aspects performance of B.mori silk fabrics. These three aspects are respectively whiteness values, yellowness index and mechanical properties. The results show that two ultraviolet aging experiments are a significant correlation. However, correlation factors of two ultraviolet aging experiments are different from the characterization of different properties changes of B.mori silk fabrics. Moreover, correlation factors are also dissimilar because of different varieties of B.mori silk fabrics.In this thesis, grey theory and BP neural network model, respectively, predict outdoor natural aging mechanical properties of B.mori silk fabric. The results show that new information GM(1,1) model is predicting better than GM(1,1) model and residual GM(1,1) model. BP neural network directly establishes nonlinear relationship between influence factors and mechanical properties of B.mori silk fabric. Influence factors include average temperature, relative humidity, wind velocity, ultraviolet intensity and sunshine hours in the natural aging process. In addition, BP neural network prediction results are significantly higher than the prediction of grey model. |
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