Thermal study of Bombyx mori silk fibroin film obtained through degumming process for biomaterial application

Silk fibroin of Bombyx mori cocoon has shown promising potential as a biomaterial for biomedical applications. In the present study, silk fibroin film was successfully fabricated from the regenerated silk fibroin solution prepared from the dissolution of degummed silk fiber in calcium nitrate solution. The degummed silk fiber exhibited markedly improved solubility in calcium nitrate solution. The thermal stability studies of raw cocoon shell, demineralized cocoon, degummed silk fiber and silk fibroin film were characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Three main stages in thermogravimetric analysis curves were observed. The initial mass losses were observed at 70, 69, 58 and 83 °C in samples of raw cocoon shell, demineralized cocoon, degummed silk fiber and silk fibroin film, respectively, which is related to the loss of bound water molecules. Silk fibroin film has higher content of water molecules among other samples. The second stage showed the mass losses at 265, 245, 265 and 246 °C to above the respective samples, and third stage showed larger mass losses at around 350 °C. The differential scanning calorimetry (DSC) study exhibited the endothermic peaks in all four materials. The Fourier-transform infrared spectroscopy (FTIR) results revealed that all samples exhibited the presence of Amide 1, Amide II and Amide III. Higher water content was found in the silk fibroin film as compared to other samples. An intricate surface morphology of the silk fibroin film was revealed using scanning electron microscope (SEM). Therefore, the present study will help in understanding the thermal stability of silk fibroin film for the potential utilization as a biomaterial for biomedical applications.