Preparation of recycled dissolving pulp from waste dark-color dyed cotton-polyester denim fabrics with sulphur dyes

It is very important and challenging to efficiently and eco-friendly recycle the waste cotton textiles, especially for the dyed cotton-polyester blended textiles due to their complex dye composition and recovery of cotton components from them. Here, we proposed a recycling route for waste dark-colored cotton-polyester denim fabrics containing sulphur dyes, involving decolorization, alkali cooking for pulp and bleaching. Thiourea dioxide (TDO) was utilized as a reducing agent to remove the sulphur dyes of the fabrics in NaOH solution system, and the effects of TDO dosage, temperature and time on decoloring efficiency were discussed. Alkali cooking with hydrogen peroxide was used to prepare cellulose pulp and remove polyester fiber components simultaneously. Then the prepared pulp was bleached through the hydrogen peroxide/tetraacetylethylenediamine to further improve its whiteness. The dissolving pulp obtained from the dark-blue and black denim fabrics had the CIE whiteness indices of 89 and 65, and the degrees of polymerization of 522 and 565, respectively. This study provided a new approach for the recycling and reuse of waste cotton textiles.