Structural changes induced in tussah silk (Antheraea pernyi) fibroin films by immersion in methanol

Abstract The crystalline transition induced by immersion in a methanol/water mixture of tussah silk fibroin (from Antheraea pernyi) film obtained by casting from a 1% solution was studied by x‐ray diffraction, differential scanning calorimetry, and infrared spectroscopy. The molecular conformation of the fibroin, consisting mostly of the α‐helix and random‐coil forms, was transformed into a random‐coil and β‐rich conformation containing only a small amount of α‐helix after immersion for no more than 5 min. The intersheet packing of the β‐crystal of the original tussah silk fibroin film was imperfect in the early stage of immersion. However, crystallization proceeded further when the immersion time exceeded 10 min. As a result the sheets in the β‐form crystal became closely packed because of the decrease in the content of the random‐coil form. The exothermic peak, which appeared at 226°C in the original fibroin and was attributed to the random‐coil → β‐structure transition, disappeared completely after immersion for 5 min.