Regenerated protein fibers .2. Viscoelastic behavior of silk fibroin solutions

The dynamic viscoelastic behavior of a concentrated solution of silk fibroin dissolved in the ''MU'' solvent is measured. The dynamic viscosity eta' and dynamic elasticity G' increase with increasing concentration of silk fibroin at constant frequency; however, the increasing frequency decreases eta' and G' at a constant concentration of silk fibroin. When the mixing ratio of C2H5OH/H2O in the ''MU'' solvent is increased at a constant concentration of LiBr . H2O, eta' and G' sharply increase at constant frequency. If the LiBr . H2O concentration is varied in the ''MU'' solvents whose ratio of C2H5OH/H2O is kept constant at 100:0, both eta' and G' are greater for LiBr . H2O concentrations of 50% by weight compared to concentrations of 40% by weight. The dependence of eta' on the temperature of the solution can be predicted by Andrade's viscosity equation. Spinnability improves when the SF concentration is increased. (C) 1997 John Wiley & Sons, Inc.