Silk fabric protection obtained via chemical conjugation of transglutaminase and silk fibroin reinforcement

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 beta-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.