Probing the photo-degradation of silk fibers is helpful to protect silk cultural relics. Studying the interactions between sericin and fibroin is essential for understanding the ageing degradation of silk fibers. Fourier transform infrared spectroscopy studies demonstrate that compared to the silk fibers under 38℃ water, the variety of β-sheet structure under ultraviolet (UV) irradiation with or without water increases and then decreases due to the removal of sericin and the damage to the peptide chains. Meanwhile, the mechanical properties of silk fibers are investigated by measuring the stress–strain curves and the ultimate tensile strength. The changes of E modulus on strain ε are calculated and the results are used to describe the mechanism of elastic, elasto-plastic and plastic strain in silk fibers under stretching. In addition, the stress degradation rates of silk fibers indicate that the synergetic role of water and UV irradiation can cause the breakage of crosslinks in the fibers with the increase of ageing time. The calculation of artificial degradation life estimation also shows that the existence of water affects the life of silk fibers. This study demonstrates that the appropriate condition can be employed for the protection of ancient silk fabrics.
Historic silk fabric is an important part of Chinese precious cultural heritage and its protection has always been a major challenge. This paper proposes a bio-safety method by the chemical conjugation of transglutaminase (TGase or TG) and sodium caseinate (SC), which produced a macromolecular polymer between protein molecules and enhanced silk fabrics. The changes of the mechanical properties of the reinforced silk fabric after washing by 10 cycles were not obvious, indicating good washing durability. After TGase and SC reinforcement, the silk fibroin (SF) solution was sprayed on the surface of silk fabric to improve the mechanical properties, where the secondary structure were formed by the self-assembly of SF to improve the mechanical properties. Therefore, the breaking stress attained the maximum value when the SF solution concentration was 1.0%. Meanwhile, the breaking stress increased by about 20.89% compared with untreated silk fabric. When the artificially alkali aged silk fabric is reinforced, the breaking stress and strain of the reinforced sample increased by 37.77% relative to the alkali aged fabric. The surface morphology and secondary structure transformation of the samples were also analyzed by scanning electron microscopy and Fourier transform infrared spectroscopy, respectively. The results indicated that a significant SF layer was introduced on the surface of the silk fabric and the β-sheet structure increased due to the synergetic role of the macromolecular polymer and SF. Moreover, it is concluded that an increase in temperature and humidity will result in a decrease in the preservation index, which caused the degradation of silk fabric and proved that the preservation time of the reinforced silk fabric in the same environment was longer than that of the unreinforced sample. The biological enzyme chemical conjugation with silk fabric and physical combination of the pure SF solution is expected to be applied to the protection and enhancement of silk cultural relics.
The design of water-resistance and breathable materials applied to the protection of a historical silk textile has raised considerable interest for their highly practical potential. Thus, simple and functional composite coatings have been investigated and applied on Bombyx mori silk fabrics by spraying silk fibroin and a water soluble siloxane emulsion enriched with silica nanoparticles (12 nm). The layer of spraying silk fibroin on the surface of the silk fabric resulted in mesoscopic molecular network reconstruction by hydrogen bonds and crosslinking of ethylene glycol diglycidyl ether to improve the physical property of the silk fabric. By systematically investigating silica composite treatment, it was found that the sample treated with silica composite coatings possessed a good hydrophobic property, in which the static contact angles increased from 43.27° to 145.77° for uncoated and coated samples, respectively. As determined by Fourier transform-infrared spectroscopy analyses, hydrophobic components such as Si-O-Si, Si-O were successfully attached to the silk fabric. The scanning electron microscopy images and the energy-dispersive X-ray spectroscopy map point distribution images showed that the coating of the silica composite forms a uniform nano-scale structure, which improved the waterproof and breathable performance. Compared with uncoated fabric, the silica composite treatment was endowed with enhanced air permeability of 446.47 mm/s. After the abrasion and washing cycles, high durability of the coated fabric was demonstrated. Excellent hydrophobic capability could help silk fabric avoid the destruction of any harmful pollutant, such as light, bacteria, sewage and so on. Furthermore, the proposed relationship between the adhesive structure and the waterproof/breathable property is applicable in the design of functional silk textiles with different levels for protective performance.
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