Abstract: The Silk Road is a bridge for political, economic and cultural exchanges between the East and West. Silk is composed of silk protein and silk glue protein. Silk protein, accounting for about 80% of the silk component, is mainly composed of 18 amino acids such as glycine, alanine, serine and tyrosine. Some amino acids in silk are easily photochemically interacted with ultraviolet light, resulting in embrittlement of the silk fabric. Silk artifacts are often not intact after excavation, which puts forward new requirements for origin tracing of silk artifacts. Stable isotope technology is a potential method for origin tracing of unknown objects and is gradually applied to trace textile artifacts. To trace the origin of silk fabrics by using isotope technology, it is necessary to figure out the influence of dyeing and aging on the isotopes of silk fabrics.
Light has great influence on the preservation of silk fabrics. In this study, silk fabrics were mordant-dyed with natural rhamnus utilis dyestuff and under UV accelerated photoaging for 5, 10, 15 d and 30 d to simulate the possible state of silk artifacts under UV lighting. Then they were dried at 50℃ for one hour and stored in a sealed bag for further testing. The color differences of the samples were tested by a spectrophotometer. The microscopic morphology and mechanical properties of the samples were examined by scanning electron microscopy (SEM) and a universal material testing machine. The chemical structure of colored silk fabrics with different photo-aging times were tested by using fourier transform infrared spectroscopy (FTIR). And the amide III region was fitted to obtain the relative content changes of secondary structures. Stable isotope ratios of silk fabrics with different degrees of photoaging were tested. On this basis, the morphological and structural changes of silk fibers under the influence of light aging and the changes of stable isotopes of silk fibers under the condition of ultraviolet light aging were analyzed to provide basic data for the traceability of silk cultural relics. The results show that UV aging had great influence on the morphology and structure of silk fabrics. UV aging induced a rapid decrease in the color difference of silk fabrics. The color difference of mordant-dyed silk fabrics changed most obviously. Cracks were shown in the surfaces of the aged silk fibers and the mechanical properties of the aged silk fabrics were greatly reduced, with the greatest reduction happening in rhamnus utilis-dyed samples. The β-sheet structure of the silk fibers was destroyed after aging. More heavy carbon isotopes were left in the aged silk fabrics compared with the control samples, especially for the mordant-dyed silk fabrics.

Key words: rhamnus utilis, plant dyeing, silk fabric, ultraviolet aging, secondary structure, stable isotopes

摘要： 为探究紫外光照射后草木染丝织品文物的形貌、结构和稳定同位素的变化规律，以冻绿染丝织品和醋酸铁媒染丝织品为实验对象，模拟在紫外光照条件下染色丝织品文物可能的状态，首先使用天然冻绿染料提取色素结合醋酸铁媒染剂对丝织品进行染色，并制备铁媒染丝织品，再对其进行紫外光加速老化；然后利用分光测色计、扫描电镜、万能材料试验机、红外光谱仪和稳定同位素质谱仪进行色差变化、微观形貌、力学性能、二级结构及稳定同位素表征。结果表明：紫外光会导致丝织品颜色变化，其中铁媒染丝织品的色差变化最明显；蚕丝纤维表面老化后会出现不同程度的裂隙，且力学性能显著降低；蚕丝纤维二级结构中的β-折叠结构遭到破坏；丝织品中的碳、氮稳定同位素比值在紫外光老后有所增大，而铁媒染样品变化更加显著。研究结果有助于天然植物染料染色丝织品文物的保护，在保存或展览时应避免紫外光的照射；天然染料染色丝织品时应注意媒染剂的使用。

关键词: 冻绿, 草木染, 丝织品, 紫外光老化, 二级结构, 稳定同位素