1973 Volume 1 Issue 1 Pages 22-26
The dynamic and thermal properties of silk fibroin of various conformations (random coil, α-form, and β-form) were investigated. Samples of silk fibroin films and well-oriented β-forms of degummed silk, raw silk, and silk gut were used.
The temperature dependence of dynamic modulus (E') for random coil, α-form, and β-form of silk fibroin film was measured. Below 100°C, E' decreased with increasing temperature. This is probably due to the evaporation of water contained in the samples. Above 150°C, E' decreased. The decrease may be caused by molecular motion of the main chains or by the partial decomposition of silk fibroin. E' for silk fibroin in the random coil conformation increased around 180°C. This increase is considered to be due to the crystallization of the silk fibroin. For the degummed silk, raw silk, and silk gut, E' decreased slowly up to about 160°C. The loss tangent increased slowly up to about 100°C, being due to the evaporation of water in the random coil, α-form, and β-form samples. The random coil sample showed a dispersion peak at around 180°C, which is caused by the crystallization of silk fibroin. The loss tangent increased in α-form and β-form samples at 150°C. This is caused by the molecular motion of main chains or the partial decomposition of silk fibroin. For the degummed silk, raw silk, and silk gut, a dispersion peak was observed at 265, 265, and 250°C, respectively.
The decomposition peak in DTA curve appeared at 290, 294, and 296°C for the random coil, α-form, and β-form, respectively. For the random coil, the exthothermic peak appeared at 218°C, which is caused by β-form crystallization. The decomposition peak in the raw silk, degummed silk, and silk gut appeared at 376, 393 and 310°C, respectively.