To provide composite fibers having practically sufficient whiteness without causing embrittlement and deterioration of soybean protein fibers and falling-off of protein components in the soybean protein fibers from a fiber material even after bleaching though the fiber material obtained by mixing the soybean protein fibers produced from strained cakes of soybeans mostly disposed of as a waste material as a main raw material with cotton fibers is an environmental-friendly material while there are problems in difficult bleaching of the fiber material.
Bleaching is carried out at a temperature within the range of 50-100C by using a bleaching solution containing hydrogen peroxide and sodium hydroxide so as to have a residual ratio of the protein components in the soybean protein fibers after bleaching of 95 wt.%, and a whiteness index of the fiber material after the bleaching of 70, and exhibiting a pH within the range of 9.5-11.
OTORI YUICHI
HISHINUMA SUMIO
SHINOZAKI ATSUSHI
TORAY INDUSTRIES
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