Comparative studies of structure, thermal decomposition mechanism and thermodynamic parameters of two kinds of silk fibroin films

Abstract

The silk fibroin films from Chinese and Thai silkworms were prepared by a new method of calcium chloride-formic acid system. The films were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and thermogravimetric analysis. The morphological, molecular conformation and thermal stability of the material and the thermal decomposition mechanism were obtained as well as the kinetic parameters (activation energy E , pre-exponential factor A ) and thermodynamic parameters (Δ H ≠, Δ G ≠ and Δ S ≠), and a compare research were performed. The results showed that the structure of silk fibroin film under 1.5 wt% concentration system mainly appeared β -sheet, and the membrane structure under 3.0 wt% concentration system was dominated by random coils or α -helix; At the different heating rate, the decomposition temperature, activation energy and activation enthalpy of 3.0 wt% concentration system were all lower than those of 1.5 wt%, and the latter has better thermal stability than the former. Under the same concentration, the β -sheet content of Thai silk fibroin film is slightly higher than that of China and it had better thermal stability. It was found by Achar differential method and Coats-Redfern integration method that the thermal decomposition process of silk fibroin film follows the cylindrical symmetry (two-dimensional diffusion) mechanism at 464~ 594 K.