The effect of residual silk sericin on the structure and mechanical property of regenerated silk filament

In this study, we elucidated the effect of residual silk sericin (SS) on structure and mechanical properties of regenerated silk filament as well as on fiber formation. The dope viscosity markedly increased with increasing residual SS content in dope solution which was prepared by dissolving the silk protein in formic acid. As a result of FTIR, 13C NMR, and XRD, a small amount of SS (9.6%) contained in the filament showed highest content of β-sheet conformation and maximum crystallinity. It seems that the SS affects the structural change of SF up to a certain level by inducing the β-transition easily. The tenacity of the filaments, containing 9.6–18.9% SS, was in the range of 2.1–2.4 gf/d, which was about 50% higher than the filament without SS (pure SF). Consequently, with the enhancement of spinnability in wet spinning process, the SS can play an important role for developing the crystalline structure of SF as well as for improving mechanical properties of the regenerated silk fiber.