The spinnable dope containing 20 wt % of silk fibroin dissolved in the MU solvent (e.g., LiBr · H2O = 40 wt %, and EtOH : H2O = 100 : 0 in volume) was spun into a coagulant and subsequently drawn, to give the following results. 1 Methanol, ethanol, and isopropanol were a predominant coagulant for the dope, and the coagulant containing 10% LiBr · H2O is best. 2 Spinnability depended upon the ratio of nozzle hole length to diameter (L/D) and was improved by increasing L/D from 4 to 10. Coagulativity was not sufficient at the SF concentration of 16%, but improved by raising it up to 20%. Drawability of the spun filaments in water was improved at a temperature above 60°C. 3 The drawn fiber showed excellent mechanical properties, especially tensile toughness when as-spun fiber was drawn in water at 61°C. An X-ray diffraction diagram of the drawn fibers indicated their crystalline axes were partially oriented along the fiber axis.
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Matsumoto et al. (1996) studied this question.