Structure and molecular conformation of tussah silk fibroin films treated with water–methanol solutions: Dynamic mechanical and thermomechanical behavior

✍ Scribed by Masuhiro Tsukada; Giuliano Freddi; Nobutami Kasai; Patrizia Monti

• Publisher: John Wiley and Sons
• Year: 1998
• Tongue: English
• Weight: 169 KB
• Volume: 36
• Category: Article
• ISSN: 0887-6266
• DOI: 10.1002/(sici)1099-0488(19981115)36:15<2717::aid-polb5>3.0.co;2-o

✦ Synopsis

The thermal response of tussah (Antheraea pernyi) silk fibroin films treated with different water-methanol solutions at 20°C was studied by means of dynamic mechanical (DMA) and thermomechanical (TMA) analyses as a function of methanol concentration and treatment time. The DMA curves of ␣-helix films (treated with Ն80% v/v methanol for 2 min and 100% methanol for 30 min) showed the sharp fall of storage modulus at about 190°C, and the loss peak in the range 207-213°C. The TMA curves were characterized by a thermal shrinkage at 209 -211°C, immediately followed by an abrupt extension leading to film failure. Both storage and loss modulus curves significantly shifted upwards for ␤-sheet films, obtained by treatment with Յ60% methanol for 30 min. The loss peak exhibited a maximum at 236°C. Accordingly, the TMA shrinkage at above 200°C disappeared. The films broke beyond 330°C, failure being preceded by a broad contraction step. Intermediate DMA and TMA patterns were observed for the other solvent-treated films. The loss peak shifted to higher temperature (219 -220°C), and a minor loss modulus component appeared at about 230°C. This coincided with the onset of a plateau region in the storage modulus curve. The TMA extension-contraction events in the range 200 -300°C weakened, and the samples displayed a final broad contraction (peak temperature 326 -338°C) before breaking. The DMA and TMA response of these films was attributed to partial annealing by solvent treatment, which resulted in the formation of nuclei of ␤-sheet crystallization within the film matrix. The increased thermal stability was probably due to the small ␤-sheet crystals formed, which acted as high-strength junctions between adjacent random coil and ␣-helix domains.