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

Abstract At present, incineration and burial are the most common ways to dispose of waste cellulose which amount could reach three million tons per year, these ways not only cause serious environmental pollution but also brings a great amount of cellulose waste that could still be recycled. In this work, the chemical method is taken to study recycle of waste cellulose denim fabric, mixed sodium hydroxide and sodium hyposulfite solution were used to achieve the purpose of separating dye from waste cellulose. Only treated after 20 min, indigo separation can reach 87.33%, and the strength loss rate of waste cellulose denim fabric is only 22.24%, which could realize the recyclization of waste cellulose, and as proved, recycled indigo can be used to redye the cellulose denim fabric. The optimal conditions for indigo separation are as follows: the weight of sodium hydroxide on the fabric is 10%, the weight of sodium hydrosulfite on the fabric is 10%, the reaction temperature is 60℃, and the reaction time is 20min. According to the test results of the UV-Vis spectrophotometer, the concentration of indigo in the dye separation solution is 0.36 g/L, and the recovery rate of the dye is 75.91%. The K/S of yarn dyed with indigo separation solution can reach 1.76, which is close to the properties of yarn dyed with standard indigo.