Life Estimation And Simulation Of The Aging Process Of Silk Historical Relics

In this paper, in order to simulate the whole process of the silk historical relics, artificial aging test was carried out on the silk fibers and the properties of silk fibers under different aging condition and time were tested. The aging degree of silk fibers was characterized by measuring the mechanical properties, surface morphology, quality change, crystalline structure and secondary structure of molecular changes. The consistency and difference of the three types of aging process(hydrolysis aging, light aging and thermal aging) were summarized and discussed and the life of silk fiber was estimated by using the time-temperature equivalence principle. The following conclusions were drawn through the foregoing studies:The consistent characteristics of the three types of aging process were: The weight of silk fiber decreased after aging process, and the weight loss rate become higher with the increase of aging time. Different degrees damage of sericin and longitudinal depth trench appeared on the surface of the silk fibers and the breaking strength decreased with the increase of aging time. The internal structure of silk fiber trended to be randomization and the crystallinity of silk fiber increased first and then decreased.The different characteristics of the three types of aging process were: a) In hydrolysis aging process, the mass loss of silk fiber was remarkable, and the mass loss rate in the initial stage was not affected by the concentration of solution. The sericin gradually dissolved, the silk fibroin dispersed a single fiber and the surface of silk fibroin fiber was no longer smooth and there was a groove on the surface of silk fibroin because of alkaline treatment. Due to the different degumming degree of silk fibers, the stress-strain curve of the fiber exhibited the characteristics of bundle fiber breakage for a period of time. In terms of the internal structure change, the peak of the amide I band was transformed from 1668cm-1 to 1666cm-1, and the secondary structure transformed from β-sheet to β-turn structure, and then to β-sheet. b) In the process of light aging, a large number of cracks perpendicular to the fiber axial direction were formed on the fiber surface. The breaking elongation of silk fiber decreased obviously and the brittleness increased, while the breaking strength and modulus decreased slowly. The peak position of the amide I band at 1624cm-1 was shifted to 1649cm-1, and the secondary structure had changed from β-sheet to α-helix and random coil structure. c) In the process of heat aging, the surface defects of silk fibers included the cracks along the axial direction of fiber and the fracture of tearing type, and cracks perpendicular to the axial direction of fiber also appeared with the increase of the degree of heat aging. The mechanical properties of silk fiber were greatly influenced by temperature. The breaking strength and elongation decreased obviously with the increase of temperature. The peak position of silk fiber wasn’t shifted obviously, but the height and width of the absorption peak were changed.A method was proposed to estimate the life of silk fiber. We assume that the breaking strength loss rate reached 95%, which can be regarded as the life of the material. Under the heat aging condition, the time-temperature equivalence principle were demonstrated by the comparison of the breaking strength change under two different aging condition(different time at 200℃ and 1000 min at different temperatures). The existence life was 150 thousand years at 25℃ by calculating the shift factor. Under the condition of hydrolysis aging, the changes of the strength of silk fibers treated with different concentrations of alkali were fitted, and the aging rate and life were calculated. Under the condition of light and light wet aging, the changes of the strength of silk fibers were fitted, and the aging rate and life were calculated. In addition, oxidation, the microorganism and worms damage should be considered to estimate of silk historical relics to estimate the life of silk historical relics.