Decolorization properties and mechanism of reactive-dyed cotton fabrics with different structures utilized to prepare cotton pulp

Developing mild decolorization technology is critical for accomplishing clean pulping to overcome issues of the severe degradation of cellulose during the preparation of cotton pulp from waste cotton textiles and the high energy consumed in this preparation. The sodium hydroxide (NaOH)-sodium dithionite (Na2S2O4) system is widely used for decolorizing cotton fabrics. However, previous reports have only studied decolorizing cotton fabrics using this hybrid system and did not clarify the decolorization mechanism of NaOH and Na2S2O4 on fabric dyed with different types of reactive dyes. Therefore, in this work, according to the chromophore groups and active groups of the reactive dyes, the decolorization of cotton fibers dyed with azo monochlorotriazine reactive dyes, anthraquinone vinyl sulfone reactive dyes and diazobismonochlorotriazine reactive dyes was studied. The decolorization mechanism of NaOH and Na2S2O4 on cotton fabrics dyed with different types of reactive dyes was clarified by employing NaOH and Na2S2O4 separately and in combination. Fourier transform infrared spectroscopy, X-ray diffractometer and extension testing were used to explore the effects of decolorization on the chemical structure, crystalline structure, and physical and mechanical properties of cotton fabrics. This work provides a theoretical basis for the decolorization of cotton fabrics dyed using different reactive dyes.