Abstract
The dynamic mechanical and thermal properties of drawn silk fibroin have been investigated. The conformation of silk fibroin treated by methanol or other organic polar solvents is known as β-form, while that of untreated and undrawn specimens is known as α-form. The latter can be transformed to β-form by mechanical drawing.
The dynamic moduli (E') of untreated silk fibroin specimens drawn in the draw ratio of 1, 2 and 10 were 7.5×109, 2.5×1010 and 1.5×1011dyne/cmcm2 at 30°C, respectively, where as those of the methanol-treated specimens were 1.6×1010, 3.5×1010 and 2.0×1011dyne/cmcm2, respectively.
The temperature dependence of dynamic modulus was determined. Below 100°C, the modulus decreased with increasing temperature, which is considered due to the water evaporation in the specimen. Above 160°C, the modulus still decreased but more slowly, which is caused by the molecular motion of main chain or a partial decomposition of silk fibroin. The tanδ curve showed the evaporation of water at temperatures below 100°C for the drawn specimens and the relaxation of the main chain at around 240°C for the well-oriented β-form specimens. The peak due to the relaxation of the main chain was observed at around 230°C and 240°C for α-and β-forms, respectively.
There were two endothermic peaks in DTA curves: One is due to the evaporation of water at the temperature around 100°C and the other at 270°C for the undrawn α-form specimen and 290°C for the undrawn β-form specimen. The decomposition peak appeared at about 320°C for well-oriented specimens.
