2014 Volume 22 Pages 39-45
Gel-like liquid silk samples were collected from the middle division of the silk glands of fully grown larvae of domestic Bombyx mori silkworm 1 day before spinning or cocooning. The samples were then immersed in distilled water and kept at 4°C in a refrigerator for 2 days, during which time the fibroin and sericin molecules gradually dissolved into the water. The liquid silk solution was then cast on a polystyrene dish and dried at 4°C. The as-cast films were subjected to water annealing or immersion in ethanol, or both, and the crystallization behavior of the fibroin fraction was analyzed by wide-angle X-ray measurement. Normally the fibroin shows two types of crystal morphology—silk I or silk II—depending on the crystallization temperature. In the case of liquid silk containing both fibroin and sericin fractions, the fibroin molecules had a silk II crystal morphology after water annealing treatment at room temperature, whereas usually silk I crystal morphology would have been generated if only the fibroin molecules had been treated. A certain mechanism established between the fibroin and sericin fractions seems to have controlled the crystallization behavior of the fibroin.