Dissolution of Bombyx mori silk fibroin in the calcium nitrate tetrahydrate-methanol system and aspects of wet spinning of fibroin solution

There are still several problems associated with the spinning of dialyzed silk fibroin solutions. In this work some of these problems have been examined. The calcium nitrate tetrahydrate-methanol system was used to dissolve the silk fibroin. A compositional phase diagram was constructed at various concentrations of the solvent system. Regenerated fibroin powders from undialyzed fibroin solution in several coagulants showed different conformations. Regenerated powders from several coagulants except methanol and ethanol were resoluble in water. Atomic absorption analysis revealed that the calcium cations strongly interact with fibroin molecules in dialyzed fibroin solution, which may interfere with the regeneration of a strong fiber. Kinetic studies to determine the diffusion coefficient of methanol into dialyzed and concentrated fibroin solution were reported. The properties of both original and regenerated fibroin such as solubility in water and thermal behaviors using DSC were compared. Regenerated fibroin fiber was spun by the wet spinning method. An X-ray diffractogram showed that the regeneration process decreased the crystallinity of regenerated fibroin fiber. SEM images of the surface and cross section of the regenerated fibroin fibers were discussed.