Abstract: The change of crystal structure and crystallinity of silk fibroin(SF) in the process of becoming insoluble by adding glycerol was studied. The blend silk fibroin films were casted by silk fibroin solutions mixing with glycerol at a series of ratios at room temperature. The water-content, solubility, structure, and mechanical properties of the blend films were measured. The results show that with the content of glycerol increasing, the solubility decreases. The blend films became insoluble when the mass ratios of glycerol/SF are more than 10%. When the content of glycerol is low, there is a little of Silk Ⅱ structure and almost no Silk Ⅰ structure in blend film. With glycerol increasing, the crystallinity of Silk Ⅰ  increases while that of Silk Ⅱ decrease in blend film. When the content of glycerol exceeding 10%, in which content that silk fibroin become insoluble, the crystalline structure of SF is mostly changed into Silk Ⅰ and there is almost no Silk Ⅱ structure. Mechanical properties indicated that glycerol could significantly improved the flexibility of silk films. In summary, the crystal structure is changed to Silk Ⅰ and the crystallinity of silk fibroin is increased so that the solubility of silk fibroin is significantly reduced by adding glycerol when casting film.

Key words: Glycerol, Silk fibroin, Film, Crystal structure, Crystallinity, Mechanical property