SYNOPSISThe spinnable dope containing 20 wt % of silk fibroin dissolved in the MU solvent (e.g., LiBr * H 2 0 = 40 wt %, and EtOH : H20 = 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 -H20 is best.2. Spinnability depended upon the ratio of nozzle hole length to diameter (LID) and was improved by increasing LID 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 61OC. An X-ray diffraction diagram of the drawn fibers indicated their crystalline axes were partially oriented along the fiber axis. 0 1996 John Wiley & Sons, Inc.

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An alcoholic-aqueous solution of LiBr rH 2 O is a useful solvent for silk fibroin, if the ratio of alcohol content to water content therein is 1 or more. The mixed solvents consisting of ethanol, water, and LiBr rH 2 O showed a higher solubility if they contained a lesser amount of water. They further proved able to easily dissolve more than 20% by weight of silk fibroin. Solvents poorer in water content and richer in LiBrrH 2 O showed a higher value of [h]; Huggins' coefficient of said solutions varied within a range 0.5-1.0, the minimum appearing at a water content of about 10% weight. Fibroin molecules remained stable in those solutions. The novel solvents for silk fibroin that have been developed by us are named ''MU solvents,'' by taking the initials in the names of Matumoto/Uejima.

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