The Bleaching Of New Chemical Fibers Sensitive To Alkali By Peracetic Acid

Soybean fiber, milk fiber and polylactide(PLA) fiber are three sorts of new chemical fibers sensitive to alkali. They are easily damaged when subjected to wet processing under alkaline conditions. In order to resolve the problem that the fibers were easily damaged in the hydrogen peroxide bleaching process, peracetic acid in situ produced in the bleaching solution using hydrogen peroxide and tetraacetylethylenediamine (TAED) were successfully used to bleach these fibers. The research results were shown as follows.(a) The bleaching of soybean fiberThe high whiteness could not be obtained if soybean fiber was bleached by hydrogen peroxide, sodium dithionite and thiourea dioxide, but could be reached by hydrogen peroxide and TAED system. A very high whites of soybean fiber would be reached by the bleaching of hydrogen peroxide, sodium dithionite and thiourea dioxide, followed by hydrogen peroxide/TAED bleaching. The best bleaching results could be got by hydrogen peroxide bleaching followed by hydrogen peroxide/TAED bleaching. Hydrogen peroxide/TAED bleaching had the merits of high whitenss, changeless soybean protein content and mild conditions, but had the demerits of a greatly negative effect on the dyeability of fiber. Therefore, hydrogen peroxide/TAED was particularly suitable for the bleaching of soybean fiber of which the product was the finished one with a high whiteness demand, or was used for the very pale dyeing.The conditions of hydrogen peroxide/TAED bleaching were as follows: hydrogen peroxide 10g/L,their theoretical molar ratio 2:1, pH 6 or so, 70℃~80℃, 75min. Though the solubility of powdered and granular TAED was different, the difference in bleaching effect was not found. However, the solution temperature had greater influence on the bleaching result of powdered TAED than on granular TAED. The TAED product of high concentration had low water-solubility and restricted its application to the bleaching by cold pad batching technique.The structure regularity of polyvinyl alcohol component in soybean fibers was slightly decreased when the dosage of hydrogen peroxide was very high. The oxidation action of peracetic acid to the non-acetalized polyvinyl alcohol and to the basic and hydroxyl amino acids of soybean protein gave rise to the obvious decrease in the dyeability of soybean fiber.(b) The bleaching of milk fiberThe whiteness of milk fibers bleached by sodium dithionite under neutral condition was not high, but the casein content and dyeability kept changeless. Hydrogen peroxide bleaching under alkaline condition led to a high loss of casein, an obvious decrease in dyeability and fiber yellowing caused by the denaturation of polyacrylonitrile. The whiteness of fibers bleached by Hydrogen peroxide/TAED was the highest, the casein content was hardly influenced but the dyeability was reduced in a small degree.(c) The bleaching of PLA/cotton blended yarnIf PLA/cotton blended yarn was bleached by hydrogen peroxide under alkaline condition, the PLA fiber in yarn would be degraded due to hydrolysis. The yarn bleached by hydrogen peroxide/TAED exhibited almost the same whiteness as that bleached by hydrogen peroxide, and lower weight loss than that bleached by hydrogen peroxide. After bleached by hydrogen peroxide/TAED, PLA fiber did not exhibit the corroded surface of similar to that bleached by hydrogen peroxide, and its crystallinity kept changeless. Therefore the PLA component of PLA/cotton blended yarn could be completely protected.