Chemical modification of Bombyx mori silk using isocyanates

Bombyx mori silk fibers were chemically modified with various kinds of isoc yanates and diisocyanates, including phenyl isocyanate and hexamethylene di isocyanate. The reactivity of these modifying agents toward silk fibers was examined as a function of the reaction solvent, temperature, time, and iso cyanate chemistry. The use of DMSO as the solvent, bifunctional isocyanates , such as hexamethylene diisocyanate, and a temperature of 75 degreesC resu lted in higher weight gains of modified silk fibers. The physical and chemi cal properties of the modified silk fibers were studied as well. The moistu re regain tended to decrease as the weight gain increased, the extent depen ding on the kind of isocyanate used. The resistance of silk toward attack b y hot acid and alkali was generally enhanced by a reaction with isocyanates , the only exception being phenyl isocyanate, which induced a drop of alkal i solubility. The tensile strength remained almost unchanged, regardless of chemical modification, while elongation at break decreased. The optical pr operties and the thermal stability of the modified silk fibers were not inf luenced by the reaction with isocyanates, suggesting that the fine structur e of silk remained unchanged, regardless of chemical modification. (C) 2001 John Wiley & Sons, Inc.