Method for stabilizing the hygral expansion behavior of protein fiber products

A method for stabilizing the hygral expansion behavior of protein fiber products comprising:

• dissolving a polyoxirane derivative having a water-dissolving rate of not less than 95% by weight in a solvent which has a solubility parameter of 10.1 to 13.0 (cal/cm.sup.3).sup.1/2, a boiling point in a range of 101.degree.-190.degree. C., and is freely soluble in water, so as to provide a water-soluble solution;
• adding the water-soluble solution to an aqueous solution containing catalyst for oxirane compounds comprising 1-15.7% by weight of dicyandiamide, 0.8-12.5% by weight of hydroxy carboxylic acid salts, 0.75-11.8% by weight of thiocyanate, and 0.5-12% by weight of L-cysteines based on 100% by weight of the aqueous solution to prepare a treatment solution;
• immersing a protein fiber product in the treatment solution and then dehydrating the fiber product;
• subjecting the dehydrated protein fiber product to a heat treatment to cross-link the polyoxirane derivative with the protein fiber product and produce L-cystine by-products;
• and
• removing L-cystine by-products from the heat-treated protein fiber product;
• wherein the polyoxirane derivative is an ethylene or polyethylene glycol diglycidyl ether derivative represented by formula (1), or a propylene or polypropylene glycol diglycidyl ether derivative represented by formula (2);
• ##STR4## wherein in formulae (1) and (2) n=1-4.