Abstract
The amorphous silk fibroin films were prepared by casting from lithium bromide aqueous solution. It was found on the basis of the X-ray diffraction patterns that the amorphous phase was crystallized into two different crystalline forms, Silk I and SilkII, by the short-time annealing at 200°C. The fibroin films of untreated sample was found to be crystallized into silk I type in the process of heating by the DSC. The metastable Silk I type was partly transformed into Silk II type by longer annealing. The films were stretched up to 2.7 times after being immersed in 80% ethanol aqueous solution for 30s. The strength and Young's modulus of the drawn films increased and elongation decreased with increasing the draw ratio. In the case of low draw ratio, crystallization occurred without any orientation. The degree of crystal orientation of Silk I and Silk II types increased, with the increase in the draw ratio of sample. The increase in the degree of crystallinity caused by annealing and stretching treatment was accompanied by the phase transformation from amorphous to Silk II. This fact was also supported by the DSC result.
