Chemical recycling of waste cellulose denim fabric and re-dyeing process

The predominant methods of cellulose waste disposal, potentially amounting to an annual volume of up to three million tons, encompass incineration and burial. Unfortunately, these practices not only induce substantial environmental degradation but also dissipate considerable quantities of recyclable cellulose material. Within the context of this investigation, we employ a chemical approach to explore the recycling of discarded cellulose denim fabric. A combination of sodium hydroxide (NaOH) and sodium hyposulfite (Na₂S₂O₄) solutions is harnessed to effectuate the separation of dye from the cellulose waste. Remarkably, after a mere 20 min treatment, the separation efficiency for indigo exceeds an impressive 87.33%, while the tensile strength diminishment of the waste cellulose denim fabric stands around 10 ~ 20%. This outcome not only show the viability of cellulose waste recyclization but also corroborates that recycled indigo can be utilized for re-dyeing cellulose denim fabric. Based on the UV–Vis analysis, the indigo concentration in the dye separation solution registers at 0.36 g/L, with a notable dye recovery rate of 75.91%. Furthermore, the K/S value (ratio of absorption to scattering of light) for yarn dyed with the indigo separation solution attains 1.76, closely approximating the properties exhibited by yarn dyed with standard indigo.