The thermal response of tussah (Antheraea pernyi) silk fibroin films treated with different water-methanol solutions at 20 degrees C was studied by means of dynamic mechanical (DMA) and thermomechanical (TMA) analyses as a function of methanol concentration and treatment time. The DNLA. curves of alpha-helix films (treated with greater than or equal to 80% v/v methanol for 2 min and 100% methanol for 30 min) showed the sharp fall of storage modulus at about 190 degrees C, and the loss peak in the range 207-213 degrees C. The TMA curves were characterized by a thermal shrinkage at 209-211 degrees C, immediately followed by an abrupt extension leading to film failure. Both storage and loss modulus curves significantly shifted upwards for beta-sheet films, obtained by treatment with less than or equal to 60% methanol for 30 min. The loss peak exhibited a maximum at 236 degrees C. Accordingly, the TMA shrinkage at above 200 degrees C disappeared. The films broke beyond 330 degrees 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 degrees C), and a minor loss modulus component appeared at about 230 degrees 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 degrees C weakened, and the samples displayed a final broad contraction (peak temperature 326-338 degrees 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 beta-sheet crystallization within the film matrix. The increased thermal stability was probably due to the small beta-sheet crystals formed, which acted as high-strength junctions between adjacent random coil and a-helix domains.