STRUCTURAL-CHANGES INDUCED IN TUSSAH SILK (ANTHERAEA-PERNYI) FIBROIN FILMS BY IMMERSION IN METHANOL

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 alpha -helix and random-coil forms, was transformed into a random-coil and beta -rich conformation containing only a small amount of alpha -helix after immersion for no more than 5 min. The intersheet packing of the beta -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 beta -form crystal became closely packed because of the decrease in the content of the random-coil form.