Toward closed loop recycling of polyester fabric: Step 1. decolorization using sodium formaldehyde sulfoxylate

Although polyethylene terephthalate (PET) fibers comprise the largest single fiber type used in the global textile community, recycling of dyed PET-based fabric is limited, resulting in the disposal of considerable amounts of PET fabric in landfills every year. Because PET does not readily biodegrade, interest in recycling some or all of the dyed textiles derived from this substrate is of interest. A step toward achieving this vision was investigated in this study, namely the development of an effective decolorization process. In this study, sodium formaldehyde sulfoxylate (SFS) was employed to decolorize disperse dyes developed for PET and it was found effective for decolorizing C.I. Disperse Yellow 42, C.I. Disperse Orange 30, and C.I. Disperse Blue 56 in water/acetone media and the process was extended to the decolorization of dyed PET fabric. An optimized combination of treatment time (30 min), water to acetone ratio (1:2), SFS concentration (10 g/L), temperature (100 °C), and liquor ratio (50/1) was found to give good color removal for a range of well-known and widely used disperse dye types. Fabric strength assessments were also investigated and it was found that SFS decolorization had no influence on PET strength, as judged by intrinsic viscosity and bursting strength measurements. It was also found that the acetone component of the decolorization medium could be recovered and reused. •Sodium formaldehyde sulfoxylate (SFS) effectively decolorizes dyed PET fabrics.•Decolorizing PET at 100 °C does not degrade the fibers.•A co-solvent system was developed for efficient decolorization using SFS.•Examples of disperse dyes that can be decolorized by SFS are presented.•An optimized method for disperse dye decolorization is reported.