Waste cotton textiles can be decolorized with the NaOH/Na2S2O4 reducing system with mild and effective results. Nevertheless, this system consumes substantial amounts of Na2S2O4, resulting in an inefficient decomposition process. The present study proposed a two-step NaOH/Na2S2O4 method to decolorize the reactive-dyed cotton fabric. The decolorization mechanism of NaOH and Na2S2O4 was investigated based on the decolorization kinetics. The results showed that Na2S2O4 decolorized the dyed cotton fabric more quickly than NaOH. In the reduction system, the decolorization mechanism of NaOH and Na2S2O4 individually followed a three-order kinetic law. During the decolorization process, a hydrolysis reaction between NaOH and cotton fiber destroyed the covalent bond, and a reduction reaction between Na2S2O4 and the dye destroyed the chromophore. The two-step NaOH/Na2S2O4 method improved the decolorization of dyed cotton fabric by reducing the ineffective decomposition of Na2S2O4. Compared to traditional methods, the two-step method endowed the decolorized fabric with a 16% higher CIE L value. Notably, the decolorized cotton fabric retained about 90% of its breaking strength.
It is critical to develop the mild decolorization technology to accomplish clean pulping in order to overcome the issues caused by the high consumption of energy and severe degradation of cellulose during the preparation of cotton pulp from waste cotton textiles. Discarded cotton fabrics was treated using a technique named as the sodium hydroxide-sodium dithionite system to remove color. During the procedure, the function of decolorization parameters, the effect of decolorization treatment on the structure and properties of cotton fabrics, and mild decolorization mechanism were investigated according to the different chromogenic systems and active groups of reactive dyes, especially. The ndings demonstrate that NaOH can hydrolyzes covalent bonds between dye and cotton ber and Na 2 S 2 O 4 destroys chromophores to achieve decolorization. The chemical makeup and crystal structures of cotton cellulose are barely affected throughout the decolorization process. It is worth noting that the strength of the decolored cotton fabric can be retained by more than 90%, thus not affecting the subsequent pulping requirements.
It is critical to develop the mild decolorization technology to accomplish clean pulping in order to overcome the issues caused by the high consumption of energy and severe degradation of cellulose during the preparation of cotton pulp from waste cotton textiles. Discarded cotton fabrics was treated using a technique named as the sodium hydroxide-sodium dithionite system to remove color. During the procedure, the function of decolorization parameters, the effect of decolorization treatment on the structure and properties of cotton fabrics, and mild decolorization mechanism were investigated according to the different chromogenic systems and active groups of reactive dyes, especially. The findings demonstrate that NaOH can hydrolyzes covalent bonds between dye and cotton fiber and Na2S2O4 destroys chromophores to achieve decolorization. The chemical makeup and crystal structures of cotton cellulose are barely affected throughout the decolorization process. It is worth noting that the strength of the decolored cotton fabric can be retained by more than 90%, thus not affecting the subsequent pulping requirements.
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