Posttreatment of the dry-spun fibers obtained from regenerated silk fibroin aqueous solution in ethanol aqueous solution

Regenerated silk fibroin (RSF) fibers were directly dry-spun from RSF aqueous solutions into air. To improve mechanical properties of fiber, the as-spun fibers were postdrawn in 80 vol.% ethanol aqueous solution, in which an immersion process was performed subsequently. With the increase in draw ratio, the fibers show substantial improvements of orientation and mechanical properties. Quantitative analysis of Fourier transform infrared spectroscopy indicates that the ratio of beta-sheet to a-helix conformation increases sharply at the beginning of immersion process, then approaches a constant value after 90 min of immersion. All fibers exhibit very smooth surfaces. There is no obvious relationship between the pH of the spinning dope and the mechanical properties of the regenerated fibers. The breaking stress of the posttreated fiber is improved up to 301 MPa, which approaches that of degummed silk. The posttreated fiber is over three times the breaking energy of degummed silk.