Regenerated silk fibroin films: Thermal and dynamic mechanical analysis

Abstract

Films of silk fibroin cast from fibroin–water solutions at different casting temperatures and untreated or treated after casting with methanol, were characterized by differential scanning calorimetry (DSC), under static and dynamic mode, thermogravimetric analysis and dynamic mechanical thermal analysis. DSC revealed the presence of a lower temperature endothermic phenomenon centered at about 70 °C for the as-prepared room temperature cast film, and other typical material thermal parameters – glass transition, crystallization, and thermal degradation – more or less pronounced depending on the specific preparation procedure and thermal or solvent treatment. These results were interpreted assuming progressive evolution of the random coil regions forward the more stable β-sheet conformation, as induced by the different applied preparation conditions or treatment. The low temperature endothermic transition observed in DSC (30–120 °C) corresponded in the dynamic mechanical analysis to a quite anomalous behavior, with a sharp decrease and immediate increase of E′. Conditions producing modifications of the thermal and dynamic mechanical curves, as well as analogies with the thermogravimetric analysis findings, were analyzed and discussed. DSC curves (10 K · min−1) of cast water solution fibroin films: as prepared (a) and after thermal treatment at 80 °C (b) and 150 °C (c), respectively.