Study On The Decoloring Process Of Brown Cashmere Fibers

The process of decoloring the brown cashmere fibers was studied in this paper. Four procedures, e.g. pretreatment, scouring, oxidative decoloring and reductive decoloring,were carried out. The properties including the strength, surface structure, dyeing behavior, the K/S value and length of decolored fibers and the stability of sunlight fastness were determined.An active reagent of neutrality and low temperature was selected and used in decoloring brown cashmere fibers with H2O2. The influence of the decoloring parameters on the brown cashmere fibers including the concentrations of FeSO4 and H2O2, pretreatment auxiliaries, , oxidation decoloring additives and reducing agent, the time and temperature of pretreatment, oxygen and reductive decoloring were discussed, respectively, in this research. On the basis of the whiteness index, alkali solubility, strength and the stability of sunlight fastness determination of the decolored fibers, the optimum decoloring parameters achieved.The optimum processes are listed in the followings, for pretreatment ferrous sulfate is 12% (o.w.f), sodium bisulfite 3.0 g/L, and 70℃, 30min; for oxidation decoloring the concentration of hydrogen peroxide and complex additive A are 18g/L and 3.0g/L, the decoloring temperature is 65℃,and time is 80min; or concentration of hydrogen peroxide, urea and sodium pyrophosphate are 18g/L,2.8g/L, and 2.0g/L,respectively, the decoloring temperature is 45℃,and time is 180min; for reductive decoloring the concentration of thiourea dioxide is 1.5g/L, the decoloring temperature and time are 80℃,30min, respectively.The whiteness index of the decolored sample attains to 65.13%, the alkali solubility is 27.43% by using the optimum parameters. The stability of sunlight fastness reaches 4 class. SEM shows that the surface structure of decolored samples is etched partly; also short fiber content higher and the length of the decolored fibers become shorter. No obviously change between the control and decolored fibers in dye uptake percentage and K/S value. Meanwhile, some functional groups exist in the decolored fibers are oxidized by using infrared spectrogram.