Time-Temperature Superposition of the Dissolution of Silk Fibers in the Ionic Liquid 1-Ethyl-3-methylimidazolium Acetate.

This study investigated the dissolution of silk multifilament fibers in the ionic liquid 1-ethyl-3-methylimidazolium acetate. The dissolution process was found to create a silk composite fiber, comprising undissolved silk multifilaments surrounded by a coagulated silk matrix. The dissolution procedure was carried out for a range of temperatures and times. The resulting composite fibers were studied using a combination of optical microscopy, wide-angle X-ray diffraction (XRD), and tensile testing. An azimuthal (α) XRD scan enabled the orientation of the composite silk filaments to be quantified through a second Legendre polynomial function (P2). The P2 results could be shifted to construct a single master curve using time-temperature superposition (TTS). The shifting factors were found to have an Arrhenius behavior with an activation energy of 138 ± 13 kJ/mol. Using a simple rule of mixtures, the P2 measurements were used to calculate the dissolved silk matrix volume fraction (Vm), which also displayed TTS forming a single master curve with an activation energy of 139 ± 15 kJ/mol. The tensile Young's modulus of each silk composite filament was measured, and these results similarly formed a master curve with an activation energy of 116 ± 12 kJ/mol.