Animal fiber superior in shrink proofing and method for preparation thereof

A modified animal fiber

• having a surface morphology that is substantially the same as that possessed by the fiber in its un-modified form, the modified animal fiber comprises chemically modified epidermal tissue epidermal tissue that exhibits an absorption band for —SO3H group having a relative absorbance of not less than 0.1 and an absorption band for —S—SO3Na group (Bunte salts) having a relative absorbance of not less than 0.08, when measured using reflection FT-IR having an absorption band corresponding to amide I set to 1,
• the epidermal tissue having epicuticle layers which afford a water repellency, confirmed by an Allwörden reaction, that is substantially the same as that possessed by the fiber in its un-modified form,
• wherein the modified animal fiber exhibits shrink proofing of an area shrinkage rate of not more than 8% in a three-hour aqueous washing when measured as a felting shrinkage rate in conformity with Woolmark Test Method 31 and pilling resistance of not lower than third class in JIS L-1076.6.1A method;
• said modified animal fiber produced by a process which comprises:
• a) a first step in which a cystine —S—S— bond in cuticle layers on surface of the fiber is subjected to primary oxidation with an oxidizer having an ability to oxidize the —S—S— bond in the cuticle layers by a pad steam treatment of the modified animal fiber with an aqueous solution of oxidizing agent under acidic conditions to contain a state rich in mono-oxidized state,
• b) a second step in which the primary-oxidized —S—S— bond is subjected to an oxidation treatment with ozone being conducted by direct blowing 5 μm or less ultrafine bubbles of an ozone/oxygen-mixed gas to the primary-oxidized animal fibers in an aqueous, acidic treating liquid at a pH of 1.5 to 2.5 and at a temperature of 30 to 50°C., into higher order oxidized state containing di, tri or tetra-oxidized state or a mixture thereof, and
• c) a third step in which said —S—S— bond in higher oxidized state is subjected to reductive cleavage.